Newly Published Articles - Encyclopedia of the Cosmos

Newly Published Articles - Encyclopedia of the Cosmos http://www.eofcosmos.org/ Thu, 01 Jan 1970 00:00:00 GMT 15 en-us matthew.wallace@corp.manyone.net http://www.eofcosmos.org/e/i/header_logo.gif Encyclopedia of the Cosmos http://www.eofcosmos.org/ Gravity: Gauge Field http://www.eofcosmos.org/article/Gravity~_Gauge_Field <p>Apart from the ambiguous experimental evidence that gravitational radiation exists but its quantal effects are unmeasureable, what compelling theoretical evidence do we really have that gravity should be expressable as a field theory similar to QED, QCD and Electroweak theory which form the basis of the Standard Model? </p><p>We have already seen how the graviton has an upper limit to its possible rest mass which is 100 trillion times lower than the photon itself. In addition to being massless, the graviton must have a spin assignment of 2 units so that the equation that defines its action looks like Einstein's equation for the gravitational field represented by a two-index field, $g_{\mu \nu}$. Steven Weinberg also proved an important theorem in 1964 which showed that spin-2 particles have to couple to all other particles and fields with a universal strength. So, even without a single clue to what such a theory ought to consist of, we can already specify with some certainty what the properties of the quantum of gravity ought to look like. The graviton has all the right properties as a theoretical particle to be the carrier of gravity, now all we have to do is create a field theory to go along with the particle. </p><p>This takes us smack into two hard questions: can such a theory of gravitons be described by the same class of theories that have proven so effective in the Standard Model, namely, the "non-Abelian gauge field theories? Also, can it be shown that graviton quantum field theory is free of infinite answers just as QED and QCD are now known to be thanks to the renormalization technique.</p><p>In 1956, Ryoyu Utiyama at the University of Osaka showed that, just as in the case of electromagnetism and Yang-Mills theory, gravity can also be expressed as a similar kind of gauge field. This was a significant new finding for gravity since it confirmed that gravity was of the same class of theory as ones that were already proving to be important as the foundation for understanding the other three forces. When you think about it, this is a rather astonishing result because gravity sure seems to look different than the other forces.</p> <p><a href='http://www.eofcosmos.org/article/Gravity~_Gauge_Field'>Read Full Article...</a></p> http://www.eofcosmos.org/article/Gravity~_Gauge_Field Wed, 11 Jun 2008 04:17:19 GMT Gravity: Canonical Quantization http://www.eofcosmos.org/article/Gravity~_Canonical_Quantization <p>The second program called 'Canonical Quantum Gravity' theory has a very different parentage. Following the established mathematical techniques developed by Schroedinger and Dirac, Einstein's equation for gravity gets rewritten, and it is in this new form that it can be analyzed for a consistent set of 'operators' and 'states' following conventional quantum mechanics. This forces quantum gravity theory to come out looking like a respectable quantum theory, but in which the dynamics of 3-D geometries play a key role, and the new Hamiltonian formulation describes how a system, the complete 3-D geometry of the universe, changes from state to state. Whereas quantum mechanics depends on considering the histories of particles as they move through space-time, quantum gravity must, in addition, consider all possible geometries of space as they unfold in time.</p><p> </p> <p><a href='http://www.eofcosmos.org/article/Gravity~_Canonical_Quantization'>Read Full Article...</a></p> http://www.eofcosmos.org/article/Gravity~_Canonical_Quantization Wed, 11 Jun 2008 04:15:40 GMT Early Cosmologies http://www.eofcosmos.org/article/Early_Cosmologies <p class="MsoNormal"> </p> <p class="MsoNormal">As humans struggle to understand the universe, we are like explorers on a strange island in an unknown sea. At this point in our explorations we know that the island is made of rocks and grains of sand. We know how big it is, we know that the sea is large, and we know that there are many other islands out there in the distance. Now we ask a series of deeper questions about our larger environment. Do the islands go on forever? Does the sea go on forever? Does our world have an edge, or is it infinite? These are questions that astronomers have only just begun to answer with some confidence.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">Cosmology is the study of the size and structure of the universe - in other words, the "geography" of the universe as a single system. Our subject is the universe, defined as all matter and energy in existence anywhere, observable or not. The scientific method is stretched thin in our speculation about the universe. As far as we know, our universe is unique. We cannot learn about it by direct comparisons with other universes, as we can with planets and stars and galaxies. Instead, cosmologists approach their subject by making simple and testable assumptions and by developing theories that describe the present state, origin, and fate of the universe. This speculation is informed by observations, and theories must agree with known physical laws.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">Cosmology begins with some fundamental questions about the nature of time and space, mass and energy. By answering these questions, cosmologists have been led to some startling ideas about the universe as a whole — ideas that lie far outside everyday experience. Cosmology is not the domain of scientists alone. For thousands of years, poets and priests and philosophers have pondered the universe and tried to understand its nature. Innate in the character of curious, restless humanity is the desire to understand our surroundings and to know where we came from.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">Cosmology is as old as the first ancients who looked at the stars set against the velvet backdrop of night. The universe is described in the earliest surviving writings of the Babylonian, Egyptian, Greek, Chinese, and Indian civilizations. According to Indian legend, the universe is a giant egg containing land, water, animals, gods, and so on, all brought forth from primordial waters by the creator god Prajapati. A Tahitian tradition says that a creator, Taaroa, existed in the immensity of space before any universe existed, and that he later constructed the heavens and the rocky foundations of the Earth. A collection of Norse myths supposes that in the beginning there was nothing at all, with regions of frost to the north and fire to the south. The heat melted some of the frost, and from the drops of liquid there grew a giant, Ymer, who created all the inhabitants of the world. This early phase of mythological cosmology linked celestial phenomena to the spiritual life of people. We have found creation myths in almost all cultures; these cosmologies provide us with an enduring link with our early ancestors.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">The first true phase of cosmology dates back to the birth of scientific inquiry in the sixth century B.C. on the shores of Asia Minor. With the ancient Greeks, the beginnings of philosophical cosmology marked the first application of the power of reason to the universe. Observations were not central to Greek cosmology; the telescope would not be invented for another 2000 years. Instead, Greek thinkers made progress by using bold hypotheses, logic, and abstract reasoning. Anaximander believed that the universe evolved from a state of primordial chaos to the order and structure that we see today. Others, like Aristotle, thought that the universe was perfectly ordered and unchanging. The twin themes of chaos and order find a strong echo in modern cosmology.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">By the third century B.C., mathematical reasoning had become part of astronomy. Until then, most people believed that the stars lay on a two-dimensional backdrop, nestled snugly around the Earth. Euclid pulled together the theorems of geometry and laid the foundation for the idea of infinite space. Imaginary Euclidean triangles could be extended into space; distances to celestial bodies could be measured. Aristarchus used geometry to anticipate the Sun-centered cosmology of Copernicus by nearly 1800 years. The Greeks also wrestled with the uncomfortable implications of an infinite universe. Plato’s colleague Archytus summed it up this way: "If I am at the extremity of the heaven of the stars, can I not stretch outward my hand, or my staff? It is absurd to suppose that I could not; and if I can, what is outside must be either body or space."</p> <p class="MsoNormal"> </p> <p class="MsoNormal">In the 17th century, with Isaac Newton, science enters the stage of physical cosmology. Newton described gravity as a force by which every particle in the universe attracts every other particle. He realized that this principle might allow a simple description of the structure of the whole universe. Newton's theory of gravity was brilliant and audacious. For the first time in human history, the mundane motions of objects on Earth had been unified with the stately orbits of heavenly bodies. Newton viewed the cosmos as infinite in extent and filled with randomly moving stars. He argued that no other assumption would make sense. If the universe were not infinite, or if the stars were all in one part of the universe, then gravity would eventually cause all matter to clump together in one place. Only in an infinite universe does each particle feel balanced gravitational forces from other particles in all directions in the sky. There is motion in Newton’s cosmology, but the universe is static — its appearance is unchanging in time.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">There were serious conceptual problems with Newton’s cosmology. The force of gravity declines with distance but it has an infinite range. When gravitational forces acting on an infinite number of bodies spread over infinite space are added up, the amount of gravity is infinite too! Another objection to Newton’s cosmology results from asking the simple question: "Why is the sky dark at night?" This concern was first raised by Thomas Digges in 1576, but it came to be associated with the German astronomer Wilhelm Olbers over 250 years later. Olbers' paradox can be described as follows. In an infinite universe filled with stars, every line of sight must eventually intercept a star. Moving out from Earth, the brightness of a star decreases as the inverse square of the distance (F µ R-2). However, the number of stars in any spherical shell (which is 4pR2 DR, where DR is the thickness of the shell) increases with the square of the distance. The result is that the amount of light in each shell is the same, regardless of distance. The contribution of light from distant stars continues to pile up. In an infinite universe, the sum of all light from distant stars is infinite: the night sky should be ablaze with light!</p> <p class="MsoNormal"> </p> <p class="MsoNormal">The modern response to Olbers' paradox is subtle, invoking the age of the universe and the recession of distant galaxies. First, there is a distance beyond which we can see no galaxies or stars. This distance does not represent an edge to the universe, but a distance corresponding to a light travel time of 12 to 15 billion years, beyond which we see no galaxies because none had formed that long ago. In other words, the total number of photons emitted by the galaxies in their finite lifetimes is too low to create the kind of pervasive bright glow described by Olbers. A secondary effect that helps to explain Olbers' paradox is the expansion of the universe. The redshifts of receding galaxies cause the apparent energies of the photons we receive from them to be reduced from high energies (short wavelengths) to low energies (long wavelengths), because the photons are "stretched" in the expanding space. Photons received from galaxies with redshifts close to the speed of light are strongly reduced in energy.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">Newton's theory of gravity left a very basic question unanswered. Just what was this force that operated across vast distances through the vacuum of space? Newton was acutely aware of this issue and went so far as to call the idea of gravity acting instantly at a large distance "an absurdity." He absolved himself of his ignorance about the cause of gravity by saying, "I have not been able to discover the cause of these properties of gravity from phenomena, so I frame no hypothesis." We did not gain a more profound understanding of the force of gravity until early in the 20th century.</p> <p class="MsoNormal"> </p> <p class="MsoNormal"> </p> <p><a href='http://www.eofcosmos.org/article/Early_Cosmologies'>Read Full Article...</a></p> http://www.eofcosmos.org/article/Early_Cosmologies Wed, 11 Jun 2008 04:03:47 GMT Ancient Observatories http://www.eofcosmos.org/article/Ancient_Observatories <p class="MsoNormal"> </p> <p class="MsoNormal">There is an astronomical context for understanding mysterious structures like Stonehenge. Keeping a calendar was a vital job for any ancient culture. We can imagine that an enormous effort would be put into measuring and marking the changing seasons. In the absence of true understanding, we can also imagine that these structures would have a ceremonial purpose. Today, most astronomers and archaeologists agree that Stonehenge was built as a marker or ceremonial site, dedicated to observing the date of summer solstice. The avenue points from the center of Stonehenge to the position of sunrise on June 21st. Someone standing in the center of Stonehenge could see the Sun rise over a big stone, called the heel stone, on the day of solstice. (The mysterious name, "heel stone," may have come in ancient times from the Greek root, helios, for Sun.) Still more astronomical purposes have been suggested for Stonehenge, including lunar eclipse predicting, but these controversial.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">The investigation of Stonehenge’s timekeeping functions helped to create a new field of astronomy called archaeoastronomy — the study of astronomical practices in ancient societies. Astronomical temples, which were used to help calibrate the calendar for agricultural and ceremonial purposes, have been found in many parts of the world. Various examples show the rich aspects of culture that are woven into the stone monuments.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">The long span of human observations of the sky allows subtle motions to be discovered. The astronomer Hipparchus studied two centuries of star maps and realized that the direction of the north celestial pole has moved slowly across the sky. A spinning gyroscope that is not pointed straight up will wobble — its rotation axis sweeps out a circle. This conical motion is called precession, and the Earth precesses with a long 26,000-year cycle. From day to day or year to year this motion is far too small to detect. The north celestial pole has not always pointed at Polaris, and ancient cultures were aware of this steady shift. In one legend, the precession was ascribed to a great whirlpool in the Mediterranean Sea, which slowly twisted the heavens.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">The Great Pyramid in Egypt — constructed around 2650 B.C. from over two million limestone blocks weighing two tons each — is aligned almost perfectly with the north-south axis. Two airshafts point directly from the pharaoh’s tomb to the brightest star in Orion's belt. The Egyptians identified Orion with the underworld god of rebirth, and it is likely that the airshafts were intended for the passage of the pharaoh’s soul on its journey to afterlife in the heavens. One airshaft does not point at any bright star now, but if we account for 4500 years of precession, it used to point at the bright star Thuban.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">The ancient city of Chichen Itza rises out of the dense rainforest in the Yucutan peninsula of Mexico. Several buildings dating from around 1000 A.D. incorporate astronomical alignments, most notably of Venus since it was important in the Mayan religion. The Mayan calendar was based on the cycles of both Venus and the Sun. On the morning of summer solstice, the rising Sun casts a shadow on the corner of the pyramid at Chichen Itza that climbs up the structure like a snake.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">In Arizona, the Hohokam native Americans built a large ceremonial structure called Casa Grande in 1350 A.D. The rising Sun aligns perfectly with holes on opposite sides of the building only on the longest day of the year. Further north, at Chaco Canyon, the Anasazi tribe created a structure on a high promontory where light is admitted through a space between rock slabs. The gap lets in a "dagger of light" that projects onto a spiral pattern carved on the opposite wall. The placement of the Sun dagger marks both the solstices and the equinoxes. These apparitions — snaking shadows, projected beams, and light daggers — are vivid demonstration of the diverse ways that cultures have marked astronomical time.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">Not everyone uses the sky in the same way. We know that at our northern latitude, the stars move on slanting paths in the sky and they all appear to orbit in slow circles around Polaris. However, near the equator the stars rise straight out of the east and set directly in the west. Polaris may be low on the horizon or even below the horizon. In the Tropics, which is the zone between 23.5° latitude North and 23.5° latitude South, there are two days each year when the Sun is directly overhead at the zenith. The Incas of Peru and the Javanese of Indonesia both chose to fix their calendars around these notable days, when a tree or a vertical stick casts no shadow. Meanwhile, at far northern latitudes above the Arctic Circle, the Sun spends large chunks of the year below the horizon and is no use for timekeeping. The Inuit and other tribes have always used the tides to keep track of time, which is a kind of lunar calendar.</p> <p><a href='http://www.eofcosmos.org/article/Ancient_Observatories'>Read Full Article...</a></p> http://www.eofcosmos.org/article/Ancient_Observatories Wed, 11 Jun 2008 04:02:38 GMT Dividing Time http://www.eofcosmos.org/article/Dividing_Time <p class="MsoNormal"> </p> <p class="MsoNormal">In mid-northern latitudes, such as in the United States, Canada, or Europe, the Sun rides much higher above the horizon in the summer than in the winter. In the summer, it rises in the northeast, crosses the meridian nearly overhead, and sets in the northwest. But in the winter, it rises in the southeast, crosses the meridian low in the south, and then sets in the southwest. You can mark the passage of the seasons by tracking the position of sunrise or sunset on the horizon. A distant feature like a rugged mountain range makes a simple but effective measuring device.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">A calendar is a means of counting the days in a year. Ancient people did this by counting the days until the sunrise (or sunset) position moved back to its extreme northerly (or southerly) position after a cycle of the seasons — called a solar year. The earliest records we have show a count of 360 days in the year. The Egyptians had revised the count to 365 days and they added a leap year — a year of 366 days inserted every fourth year — for an average calendar 365¼ days long. By 2700 B.C., the Babylonians had refined this to a calendar of 365.26 days which was accurate to about 30 minutes in a year. This is an impressive calendar. Nearly 5000 years ago, the length of the year was known to an accuracy of better than one part in ten thousand!</p> <p class="MsoNormal"> </p> <p class="MsoNormal">Ancient observers divided the year into seasons using four special dates that we still recognize. Winter solstice is the first day of winter, around December 22nd. On this day the Sun rises and sets farthest to the south. This day has the shortest period of daylight of any day in the year in the northern hemisphere. The pre-Christian pagan cultures of England and France began the year on this date, to celebrate the return of the Sun toward the northern sky. Since the seasons vary smoothly throughout the year, it is quite arbitrary when we choose to begin the calendar. Spring equinox is the first day of spring, around March 21st. On this day the Sun rises due east and sets due west. Day and night are equal in length on this day (in the word equinox, equi- means equal and -nox means night). Other pagan cultures, such as those that worshipped the goddess Maia, began the year on this date because it marked the beginning of the cycle of new growth. Summer solstice is the first day of summer, around June 22nd. On this day the Sun rises and sets farthest to the north. It has the longest daylight period of the year. In many ancient calendars, it marked a day of celebration, when the days were long and the weather pleasant. Autumn equinox is the first day of fall, around September 22nd. On this day the Sun rises due east and sets due west and day and night are again equal.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">Primitive cultures also marked the midpoints of the calendar between the solstices and the equinoxes. These dates are February 1st, May 1st, August 1st, and November 1st. In Ireland, these festivals are all still celebrated and are known by their Gaelic names: Imbolic, Beltane, Lughnasa, and Samhain. May Day was originally a fertility festival in the pagan world, and it is still a folk festival in England. And of course the eve of November 1st is celebrated in many parts of the world, as All Saints' Day in England, as the Day of the Dead in Mexico, and as Halloween in the United States.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">You might think that knowledge of solstices and sunrise positions is useless knowledge from the ancient past. However, it has applications in the present, especially in an environmentally conscious age. Consider the layout of windows in your home or apartment. Windows facing northeast or northwest allow sunlight to enter on summer mornings or afternoons, when you are likely not to want extra heat in the house. Draperies or shades on these windows in the summer will block sunlight and save on energy bills. Windows facing southeast or southwest, on the other hand, will let in the low-angled light of the winter Sun, giving a free input of extra heat. In a house specifically designed to take advantage of these ideas, windows are placed to take advantage of the midwinter morning and afternoon Sun on the southeast and southwest side. Trees might be planted to shade the northeast, east, west, and northwest sides of the house during the summer mornings and afternoons. Roof overhangs shade southern exposures from the high summer midday Sun, while letting the low winter midday Sun warm the interior and exterior of the home.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">Most of the major divisions of time have astronomical origins. The illumination cycle of the Moon gives rise to the month. Every 29½ days there is a full Moon or a new Moon, and this cycle divides approximately 12 times into the solar year. We have found carved animal bones and other artifacts dating back 20,000 to 30,000 years in France and other parts of Europe. Some of these objects have numbers of notches that indicate that the cave dwellers were using them to count months. These portable calendar sticks are among the oldest human relics.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">There is a difference between time kept using the Sun and Moon, and time kept using the stars. The time taken for the Sun to pass through the meridian on successive days is a solar day. The time taken for a star to pass through the meridian on successive nights is a sidereal day. Since every star rises and sets a little bit earlier every day, a solar day is about 4 minutes longer than a sidereal day.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">Similarly, the time taken for the same phase of the moon to recur is the Moon’s synodic period — 29.5 days. This is longer than the time taken for the Moon to pass the same place among the stars — the Moon’s sidereal period is 27.3 days. These differences occur because the stars that would be seen in the direction of the Sun shift gradually as the Earth spins and as the Moon orbits the Earth.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">Once ancient people recognized the fixed pattern of the constellations, they discovered that five bright "stars" were different from all the others. These "stars" moved from week to week relative to the pattern of the fixed stars. They became known as planets, from the Greek word for wanderer. The planets had unusual attributes. For example, they were not found any place in the sky but always in the strip of sky occupied by the Sun and Moon. Some planets were only seen close to the Sun, others were seen far from the Sun. Some planets would even reverse their direction in the sky when viewed from week to week. Our names for the planets come from the Roman gods Mercury, Venus, Mars, Jupiter, and Saturn. (The other planets — Uranus, Neptune, and Pluto — were not discovered until the invention of the telescope, and the Earth was not yet recognized as one of the planets.)</p> <p class="MsoNormal"> </p> <p class="MsoNormal">Every culture has felt the need to create a chunk of time like a week. Ancient Egyptians used 10 days, the Babylonians used 7 days, the Assyrians used 5 days, and some West African tribes have used 4 days in the week. Our calendar is based on Roman tradition, which named the seven days of the week after the seven "moving" objects in the sky — the Sun, the Moon, and five planets. Some of these names are obvious: Saturn-day, Sun-day, Moon-day. The connections to other planets are clearer in languages that are derived from Latin such as Spanish, Italian, and French. Tuesday is Mars-day for example (Mardi in French, and Martes in Spanish). Wednesday is Mercury-day (Mercredi in French, and Miercoles in Spanish), Thursday is Jupiter-day (Jeudi in French, and Jueves in Spanish), and Friday is Venus-day (Vendredi in French, and Viernes in Spanish). So what happened to the names of these four days in English? They were named after gods from the Anglo-Saxon culture of a thousand years ago. Tuesday comes from Tiw, the Norse god of war. Wednesday comes from Woden, the supreme deity. Thursday comes from Thor, the god of thunder. And Friday comes from Frigg, the wife of Woden and goddess of love and beauty.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">Even the division of the day into hours has an astronomical origin. Egyptian astronomers used a sequence of bright stars across the sky for timekeeping at night. Twelve timekeeping stars were visible during the critical midsummer period when the Nile would flood so the night (and later the day) was divided into twelve hours. Timekeeping was very primitive until the last 250 years. The Greeks used sundials and the Romans perfected the water clock, where water could drip at a regulated rate though a small hole in a hard stone or jewel. The sand hourglass dates from 8th century Europe. Nobody could divide hours into minutes and seconds until the pendulum clock was invented in the 17th century. We can thank the Babylonians of 5000 years ago for the division of the hour into 60 minutes and the minute into 60 seconds.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">Many other features of our calendar and timekeeping spring from the pagan cult of Sun worship. Stonehenge and other great prehistoric structures were built to measure and celebrate the motions of the Sun. Many pagan traditions were borrowed by the early Christian calendar that we still follow. The year starts on January 1st. This copies the pagan cultures which began their calendar when they could detect the Sun beginning to move further north in its rising and setting position. Our rest day of Sunday follows the pagan day of worship of the Sun. Why do clocks move clockwise? In northern Europe clocks were designed to mimic the arcing motion of the Sun from left to right across the southern sky. Our habits of timekeeping are a rich brew of astronomical ideas taken from earlier cultures.</p> <p><a href='http://www.eofcosmos.org/article/Dividing_Time'>Read Full Article...</a></p> http://www.eofcosmos.org/article/Dividing_Time Wed, 11 Jun 2008 04:01:06 GMT Constellations and Seasons http://www.eofcosmos.org/article/Constellations_and_Seasons <p>For most of human history, we have been wanderers. But around 7000 to 10,000 years ago, tribes learned how to domesticate animals and cultivate simple crops. The birth of agriculture created a new need to keep track of time. Ancient people had to be aware of the cycles of seasons. It was a matter of life and death. In order to eat, they had to know when to plant, when rains would come, when the birds would migrate through their region, and when they would have to store food for the lean winter times.</p><p>We can track the seasons using either the stars or the Sun. The stars all have a fixed pattern relative to each other from year to year, like the pattern of major cities on a map of the Earth. Many ancient cultures selected specific groupings of stars or constellations to represent certain animals or mythological figures. When you see the constellations — for example Ursa Major the great bear, or Orion the hunter, or Pisces the fish — it is not obvious what the patterns are supposed to represent. You have to use your imagination! The constellations are not literal drawings on the sky, but were used as a memory aid for navigation or to pay homage to gods and myths. If you learn a few major constellations, they can help you locate the North Star and other directions in the sky.</p><p>Many constellations are extremely old. Clues in the constellation patterns, such as the names of mythical creatures, suggest that many constellations on our sky maps were designated around 2600 B.C. by Mediterranean seafarers. A few, such as Ursa Major (which contains the asterism called the Big Dipper) were known throughout Asia and also by Native Americans. We believe this constellation was first named in Asia before 10,000 B.C., and the name was carried to America by the first Americans who traversed the land bridge that crossed the Bering Strait around that time. Ursa Major is one of the oldest human cultural artifacts.</p> <p>The path traveled by the Sun with respect to the fixed stars is called the ecliptic. The Moon and the planets are always found near this path, and this strip of sky has always had special significance. Ancient people called this strip of sky the zodiac — circle of animals —and divided it into the twelve constellations that we recognize as the star signs.</p><p>The constellations on view depend on your position on the spinning globe of the Earth. Observers at the poles only ever see half the stars in the sky. Observers at the equator see all the stars each year. Any particular star rises and sets a little earlier every night. The entire set of constellations passes through the night sky once during each cycle of the seasons. This results from the Earth’s annual motion around the Sun. During each season, different constellations appear in the evening sky. For example, Cygnus the swan rides high in the summer and Orion the hunter appears in the late fall. After a full year, the pattern of constellations in the evening sky repeats its cycle. Constellations return each season, and it is fun to greet them, like old friends coming around each year.</p><p>Constellations have been used for keeping track of the seasons long before we had a scientific explanation for their motions. Hesiod was one of the first poets whose words were written down. He lived in Greece about 2500 years ago and said:</p><p>"When great Orion rises, set your slaves<br />to winnowing Demeter’s holy grain<br />upon the windy, well-worn threshing floor.<br />Then give your slaves a rest; unyoke your team.<br />But when Orion and the Dog Star move<br />into the mid-sky, and Arcturus sees<br />The rosy-fingered dawn, then Perseus, pluck<br />The clustered grapes, and bring your harvest home."</p><p>Astronomy is not only the oldest science but it is woven into the fabric of our culture in many ways. We can see this clearly when we look at look at the development of calendars and the way we divide up time.</p><p> </p> <p><a href='http://www.eofcosmos.org/article/Constellations_and_Seasons'>Read Full Article...</a></p> http://www.eofcosmos.org/article/Constellations_and_Seasons Wed, 11 Jun 2008 03:58:44 GMT Greek Astronomy http://www.eofcosmos.org/article/Greek_Astronomy <p>Ancient cultures like the Babylonians and the Egyptians could recognize patterns in the sky. They could predict astronomical events. They had accurate calendars. However, they made no progress in answering fundamental questions about their universe. How far away are the planets, the Sun, and the Moon? Why do they shine? What makes them move? Progress was made by a remarkable group of thinkers who lived in the 3rd to 6th centuries B.C. on what is now the coast of Greece and Turkey. This era marks the birth of science. </p><p class="MsoNormal"> </p> <p class="MsoNormal">The breakthrough was made by a set of philosophers who developed the basis of the scientific method. They applied logic and rigorous thought to many areas of human activity. Astronomy was just one example. They also developed new tools in mathematics to carry them forward. When Plato founded the world's first university in an olive grove outside Athens, he elevated mathematics to high intellectual status. The inscription above the main entrance read "Let Only Geometers Enter." The Greeks used geometry to move beyond the impression of the stars and planets as points of light on a fixed backdrop. They reached out to the third dimension and formed startling ideas about the true size of the universe.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">In 584 B.C. two Greek tribes were engaged in a bloody battle on the coast of Asia Minor. The poet Hesiod recorded the scene with vivid descriptions of burnished shields and flashing swords and carnage. Suddenly, the sky darkened and the air chilled with a total eclipse of the Sun. The soldiers wandered dazed and confused from the battlefield, believing they had witnessed an omen from the gods. Not far away, a man called Thales was not at all surprised. He had used Egyptian eclipse records to predict the exact date of the eclipse.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">Thales was a statesman, geometer and astronomer who lived in Miletus in what is now Turkey from 634 to 556 B.C. He is the subject of perhaps the first anecdote about absent-minded scientists. A story is told of a servant girl who saw him fall into a well and chastised him for being so preoccupied with the heavens that he failed to notice what was under his feet. Thales believed that everything in the material world derived from water. While this might seem naive, it is an important step in the development of science to suppose that all things have a source and to suppose that the source of all things is one thing. This is a basic scientific idea - the diversity of the natural world conceals an underlying simplicity.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">The ideas of Pythagoras are perfect examples of the union between mathematics and cosmology. He lived from 583 to 510 B.C. Pythagoras left no writings, so we know of his work only through the writing of his followers. By observing the phases of the Moon, he realized that the Moon is a sphere and proposed the then-unusual idea that Earth is a sphere, too. Pythagoras placed the spherical Earth at the center of the universe. He developed many ideas in mathematics, for example the famous "Pythagorean theorem" of right-angled triangles. Since a sphere is the most symmetric and perfect shape, it was natural to Pythagoras that it would describe the Earth and the orbits of the Sun, the planets, and the stars. Pythagoras established a school in southern Italy, and some of his students proposed the idea that the Earth, the planets, the Sun, and the stars all move around some distant, central "fire." Even though some of these early ideas are incorrect, we can recognize the bold and adventurous thinking of these early scientists.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">In the 5th century B.C., Anaxagoras deduced the true causes of eclipses. He noticed the curved shadow of the Earth on the moon during a lunar eclipse and realized that this observation supports the idea that Earth is round. A sphere is the only solid shape that casts a circular shadow regardless of the direction of illumination. He studied a meteorite that had fallen out of the sky in 467 B.C., and calculated that the Sun is an incandescent "stone" even larger than Greece. This idea got him in trouble when he was charged with impiety and banished for teaching heretical ideas.</p> <p><a href='http://www.eofcosmos.org/article/Greek_Astronomy'>Read Full Article...</a></p> http://www.eofcosmos.org/article/Greek_Astronomy Wed, 11 Jun 2008 03:56:59 GMT Navigation http://www.eofcosmos.org/article/Navigation <p class="MsoNormal"> </p> <p class="MsoNormal">How could you use the sky to find your way? The first orienteering skills were discovered over 10,000 years ago. If you were out hunting during the day you would watch the path of the Sun carefully, because you would have to turn around when it reached its highest point in the sky to avoid being out at night. At its highest point in the sky, the Sun indicates the direction south. The Sun can act as a clock. If you lived in a hot climate, you might need to travel at night and use the stars to guide you. Ocean voyagers must also use the stars to navigate at night. The star patterns can be a map.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">Most people are vaguely aware that they can find their way at night by the stars. They also know that there is a North Star, called Polaris, which is always in the north. But there are many other features of the sky that are familiar and useful. Night walks or camping trips offer a great opportunity to learn your way around the sky. Knowing some basic sky terminology is a useful first step. The point directly overhead is called the zenith. An imaginary line overhead, from the due south point on the horizon through the zenith, to the due north point on the horizon, is called the meridian. The Sun, Moon, and all the stars and planets rise on the east side of the meridian, cross the meridian, and set on the west side of the meridian. The ancient term A.M. (from the Latin phrase, ante meridiem, or before the meridian) refers to the first half of the daylight period, before the Sun crosses the meridian. The term P.M. (post meridiem) refers to the second half of the day, after the Sun crosses the meridian.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">It seemed obvious to ancient people that Sun, the Moon, and the stars all orbited around the Earth. There was no reason to suppose that the Earth was moving — after all, we don't feel any motion! We now know that the Earth spins once per day. The rising and setting motions of the stars are due to the Earth's rotation. The line that connects the North Pole and the South Pole is the Earth's rotation axis. For navigation, the most interesting star is the North Star or Polaris. Because the Earth's North Pole happens to be aimed at it, it neither rises nor sets but sits at the same spot above the northern horizon all night. All the other stars in the sky move slowly in circles around it. This motion is imperceptible from minute to minute, but you can see it over a period of hours or with a long exposure photograph. Polaris is a fairly bright star and thus serves as a beacon, pointing north. The Earth is like a spinning top, with the stars wheeling around two fixed points in the sky.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">Polaris reveals your latitude. The angle of Polaris above the northern horizon (measured in degrees) equals your latitude (the number of degrees you are north of the equator). For example, in most of the United States, the North Star is about 30° to 45° above the northern horizon. However, at the North Pole, Polaris is directly overhead and the stars move in concentric circles parallel to the horizon. Anywhere on the equator, Polaris is low on the northern horizon and stars rise straight out of the east and set straight into the west. The Earth's South Pole doesn’t point at any bright star, so navigation south of the equator uses other star patterns.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">Ancient navigators sighted the North Star to determine their latitude, even in the middle of the ocean or in a trackless wilderness. For example, ancient Polynesian navigators sailing from Tahiti to Hawaii could sail north until the North Star confirmed the latitude of Hawaii, then head west until they came to Hawaii. Once you have memorized the main features of the night sky, star patterns can be used for navigation too. It is too hot to travel during the day in the desert regions of the Middle East. For this reason, and because the Arabs preserved in translation the original names from ancient cultures, many of the bright stars have Arabic names (Aldebaran, Mizar, Alcor, Deneb, and others).</p> <p><a href='http://www.eofcosmos.org/article/Navigation'>Read Full Article...</a></p> http://www.eofcosmos.org/article/Navigation Wed, 11 Jun 2008 03:54:10 GMT Motions in the Sky http://www.eofcosmos.org/article/Motions_in_the_Sky <p>Imagine that it is 40,000 years ago and that you are a nomadic hunter-gatherer. Much of your life is spent in the search for food and shelter. You are familiar with the slanting path of the Sun as it crosses the sky. You know the steady shift of the length of day and night throughout the year. The slow change of the climate gives you clues to the appearance of ripening berries and the migration of herds of animals. The Sun and the stars give you the tools for navigation. At night, by the safety of a fire, you and your tribe weave stories around the changing shapes of the Moon and the patterns of the stars.</p><p>We have lost touch with the sky. Most people are only vaguely aware of the cycles of Sun, Moon and stars. Our lives are regulated by watches, and by artificial heat and light. Most of us live in urban areas where the stars are barely visible. However, for much of history this information was essential for human survival.</p><p>Here is what someone at northern latitudes would observe over the course of a year:<br />In summer, the Sun rises north of due east and the day is longer than the night. In winter, the Sun rises south of due east and the day is shorter than the night.<br />The Sun, Moon and planets traverse the same strip of sky from east to west.<br />Stars rise in the east and set in the west. They all appear to slowly rotate about a fixed point in the northern sky.<br />The pattern of stars in the constellations dos not change from year to year.<br />Any particular star rises and sets slightly earlier each night. The constellations migrate through the sky completely in one cycle of the seasons.<br />Some of the planets move irregularly among the constellations, occasionally reversing their direction of motion.<br />The Moon changes its phase on a regular cycle. A full moon is high in the sky around midnight and a new moon is high in the sky around midday.<br />Lunar eclipses are more frequent and last longer than solar eclipses. Neither occurs every month.</p><p>The Sun rises in the east and sets in the west, traveling on a slanting path across the sky. In summer, the Sun rises north of due east and the day is longer than the night. In winter, the Sun rises south of due east and the day is shorter than the night. The Sun rides higher in the sky in summer than in winter. Using a distant horizon as a marker, you see that the shifting path of the Sun repeats each time there is a cycle of the seasons. You celebrate the return of the Sun to its higher trajectory because it means that winter is easing its icy grip.</p><p>The Moon also orbits the sky along the same path as the Sun but it appears to move at a different rate. When it is close to the Sun, the Moon appears as a crescent with the lit side pointing towards the Sun. When it is on the opposite side of the sky to the Sun it is a fully lit disk. The changing face of the Moon also follows a regular pattern. The Moon is a mysterious object — it is remote yet the level of the oceans responds to it.</p><p>At night the stars also rise in the east and set in the west. Over the course of a night they rotate about a fixed point in the northern sky. As the seasons progress, different groups of stars are seen above horizon at sunset. The stars migrate completely around the sky during one cycle of the seasons. You note that the colors of different stars vary from a dull red to a brilliant blue-white. Your imagination is captured by the delicate band of light that arcs across the winter sky.</p><p>You can notice five bright points of light that move from night tonight among the fixed star patterns. You can locate these "wanderers" in the strip of sky traversed by the Sun and Moon; they do not twinkle. They also have the peculiar habit of occasionally reversing their nightly motion.</p><p>You know the sky offers surprises. Every so often the full Moon is darkened to a blood red color and then slowly brightens again. You have been told of a rare but fearsome event when the midday Sun darkens inexplicably. You can vividly imagine the disquiet of animals as they respond to the false night and the sudden chilling of the air.</p><p>You need no telescope or advanced timekeeping to measure the cycles of the sky. Humans have made a slow march towards understanding these phenomena. There is a natural reluctance of humans throughout history to accept that the Earth might not be the center and main feature of the universe. Until a few centuries ago, people thought that the celestial objects occupied an "ethereal realm" where the laws were different than on Earth. More recently comes the beginning of the idea that the same physical laws apply to the untouchable objects of space as to mundane terrestrial objects. This is followed by the application of logic and mathematics to the universe. Astronomy is "the first science."</p><p> </p> <p><a href='http://www.eofcosmos.org/article/Motions_in_the_Sky'>Read Full Article...</a></p> http://www.eofcosmos.org/article/Motions_in_the_Sky Wed, 11 Jun 2008 03:12:24 GMT Stonehenge http://www.eofcosmos.org/article/Stonehenge <p>Mysterious rings of upright stones dot the hills and dales of England. The most famous is a monument called Stonehenge, which many people know only as a ring of giant stones standing silently in an ancient field. Few people realize that other prehistoric structures abound in the nearby landscape. For example, a broad "avenue" lined by earthen banks leads out of Stonehenge across the plains for about 1/2 kilometer (1/3 mile) toward the northeast. What was the purpose of such enigmatic features? In the Middle Ages, people believed that King Arthur's magician, Merlin, built them. Others attributed them to ancient wise men called Druids. In the 1720s, a lone scholar named William Stuckley visited many of the ancient monuments and made careful drawings of these prehistoric wonders. Stuckley was the first person to record a curious fact. The avenue leading from the center of Stonehenge points exactly toward the spot on the horizon where the Sun rises on the longest day of summer.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">What could the alignment at Stonehenge mean? More than a century later, in the 1890s, English astronomer Norman Lockyer noticed that other ancient monuments were oriented according to astronomical principles as well. Lockyer rediscovered Stuckley's work and then synthesized it with his own observations to conclude that Stonehenge was a prehistoric astronomical temple designed specifically for ceremonies on the longest day of summer. According to Lockyer, ancient people from various parts of the world who lived from 3000 B.C. to 1000 B.C. knew of subtle astronomical cycles. For example, they knew how to construct calendars accurate enough to reliably plant crops from year to year. They knew of the variations in the motions of the planets among the stars. Some cultures were even able to discover that the constellations had subtly changed their shapes and positions over the centuries.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">Archaeologists and other scientists of the day ridiculed Lockyer's ideas, arguing that ancient people could not have gained such extensive knowledge. Today, most scientists agree with Lockyer. Ancient architects in various cultures sometimes used astronomical knowledge to locate and orient buildings and monuments. We should avoid two tendencies when speculating about ancient cultures. The first is to assume that such people were unsophisticated because they had primitive technology. Remember that the brain function and language skills of humans have not changed for many thousands of years — the people who built Stonehenge were just like us. The second danger comes when we ascribe modern motives to ancient cultures. Stonehenge was not an observatory in the modern sense of the word. It almost certainly had a ceremonial and spiritual function as well. We can only make educated guesses at the intentions of the builders since they left no written language.</p> <p class="MsoNormal"> </p> <p class="MsoNormal">Building Stonehenge was a terrific undertaking! The circular embankment and solstice avenue were built around 2500 B.C. During the time that followed from 2100 B.C. to 1500 B.C., workers dragged the huge stones from quarries as far as 380 kilometers (240 miles) away and erected them to form the famous structure in the center of the ring. Archaeologists think that Stonehenge's purpose gradually shifted from precise observation to ceremony; by medieval times, its original function had been forgotten. Why would ancient people go to such enormous trouble to build this monument? Why would they take such an interest in the sky and astronomy? The sky serves as a map, a clock, and a calendar. The "cycles of the sky" have been important to every culture throughout history.</p> <p><a href='http://www.eofcosmos.org/article/Stonehenge'>Read Full Article...</a></p> http://www.eofcosmos.org/article/Stonehenge Wed, 11 Jun 2008 03:09:07 GMT Gravity: String Theory http://www.eofcosmos.org/article/Gravity~_String_Theory <p>There was hardly any time to wrestle with the implications of these ideas before yet another revolution in thinking hit the theoretical fan. In 1982, John Schwartz and Michael Green announced 'Superstring Theory'. </p><p>Henceforth, particles would not be thought of as point-like concentrations ofenergy, but as 1-D, vibrating 'strings' of energy.Particle world lines would be fattened from spaghetti-like, 1-D tracks in spacetime, to macaronni-like tubes, and with this new structure, all infinities would vanish without any need at allfor renormalization. </p><p>The only problem is that: 1) Spacetime would have to have either 10 or 26 dimensions in order that the theory was self-consistent; and 2) the theory would naturally work only at energies near 10<sup>19 </sup>GeV. The lowest "mode" of string oscillation would yield particles withno rest mass at all. The next-highest mass range would be 10<sup>19</sup> GeV. </p><p>Throughout the 1980's and much of the 90's, string theorists have wrestled with forcing this "beautiful" theory to make predictions about particle physics in our low-energy world at the bottom of the energy ladder. Many feel that nature has been unkind to us by providing physicists with a 22nd Century theory, but only giving us 20th Century mathematics from which to crack openits secrets.</p> <p><a href='http://www.eofcosmos.org/article/Gravity~_String_Theory'>Read Full Article...</a></p> http://www.eofcosmos.org/article/Gravity~_String_Theory Fri, 02 May 2008 21:42:04 GMT Universe: Expansion http://www.eofcosmos.org/article/Universe~_Expansion All Big Bang cosmologies have a common non-intuitive ingredient; they predict that 3-D space grows larger as the universe grows older. It does this not by appropriating new volumes of space at its periphery, but by stretching. We can countenance the idea the the universe may have had a beginning in time, we can even accept that the universe may one day re-collapse in a blaze of fire. But the mind will simply not accept that the expansion effect described in Big Bang cosmology is not simply the movement of galaxies away from each other in space like the glowing embers of a fireworks display. The mind seems to have an easier time accepting space being infinite that it does with the prospect that space may be capable of stretching. Let's see where this fundamental idea emerges in both observations and theory. <p>For over 65 years the cosmological redshift discovered by Edwin Hubble (1889 - 1953) has endured as one of the most persuasive proofs that our universe is expanding. But at the same time, it is one of the most misunderstood and poorly explained features to our universe. By an unfortunate historical accident, the cosmological redshift is almost always confused with the more well-known Doppler Effect.</p><p>Soon after Christian Doppler's (1803 - 1853) 1842 discovery that a moving source of sound produces a measurable change in pitch, astronomers began an aggressive spectroscopic program to measure the velocities of stars and planets using their Doppler shifts. This continued through the first few decades of the 20th century culminating in the work by Vesto Slipher (1875 - 1969), Edwin Hubble and Milton Humason (1891-1972) on the so-called spiral nebulae -- distinctly non- stellar objects that also seemed to display star-like Doppler shifts. </p><p>So long as velocities of only a few hundred kilometers per second were measured, no one questioned that the frequency shifts for the spiral nebulae indicated relative motion just as they had for stars and planets. But, during the 1920's and 30's spiral nebulae with Doppler shifts of over 34,000 kilometers per second were discovered. In a letter to Willem De Sitter in 1931, Edwin Hubble stated his concerns about these velocities by saying,</p><p><strong>...we use the term 'apparent velocities' in order to emphasize the empirical feature of the correlation. The interpretation, we feel, should be left to you and the very few others who are competent to discuss the matter with authority</strong>.</p><p>Despite this cautionary note, the fact of the matter was that the redshifts measured at the telescope for the distant galaxies <strong>looked </strong>like Doppler shifts. The terms 'recession velocity' and 'expansion velocity' were quickly brought into service by astronomers and by popularizers, to describe the physical basis for the redshift. </p><p>For decades no one really bothered to distinguish between 'cosmological redshift' and 'Doppler shift'. This has in the years since Hubble's work led to an unfortunate misunderstanding of Big Bang cosmology, obscuring one of its most mysterious beauties. As noted with a hint of frustration by renowned cosmologists such as Steven Weinberg, Jaylant Narlikar and John Wheeler, </p><p><strong>"The frequency of light is also affected by the gravitational field of the universe, and it is neither useful nor strictly correct to interpret the frequency shifts of light...in terms of the special relativistic Doppler effect."</strong></p><p>Although cosmologists unanimously agree that cosmological redshifts are distinct from Doppler shifts, popularizers of cosmology have a long tradition of not emphasizing this distinction. By referring to cosmological redshifts as Doppler shifts, we are insisting that our Newtonian intuition about motion still applies without significant change to the cosmological arena. A result of this thinking is that quasars now being detected at redshifts of Z = 4.0 would have to be interpreted as traveling a speeds of more than 4 times the speed of light. This is, of course, quite absurd, because we all know that no physical object may travel faster than the speed of light.</p><p>To avoid superluminal speed, many popularizers use the special relativistic Doppler formula to show that quasars are really not moving faster than light. The argument being that for large velocities, special relativity replaces Newtonian physics as the correct framework for interpreting the world. The adoption of the special relativistic Doppler formula by many educators has led to a peculiar 'hybrid' cosmology which purports to describe big bang cosmology using general relativity, but which is still firmly mired in the rubrik of special relativity. For instance, under the entry 'Redshift' in the <u>Cambridge Encyclopedia of Astronomy</u> it is explicitly acknowledged that the redshift is not a Doppler shift, but less than two paragraphs later, the special relativistic Doppler formula is introduced to show how quasars are moving slower than the speed of light. This has now become the accepted way of explaining redshifts now used, for example, in the 1991 editions of undergraduate astronomy textbooks.</p><p>The expansion of the universe cannot be directly observed. It can only be <strong>inferred </strong>from observations of the cosmological redshift which general relativity then tells us, means that the universe is expanding. Although we can intuitively imagine galaxies moving about like balls on a billiard table, astronomers have absolutely NO conventional evidence that galaxies move. This may surprise you, but consider this: although astronomers can, over the course of years, show that the positions of stars in the sky actually change, the shifts in the positions of galaxies over the course of a human lifetime and even a million years, is impossible to detect. </p><p>Cosmological expansion is not a form of movement that any human has ever experienced. It is, therefore, not surprising that our intuition reels at its implication and seeks other less radical interpretations for it including special relativity. Here is what the expansion predicted by general relativity looks like. Imagine two galaxies permanently located at the positions identified by their Gaussian coordinates, (x_1 , y_1 , z_1 ) and (x_2 , y_2 , z_2 ) at one moment in Cosmic time. Using the form of the FLRW metric appropriate to that age, we determine that they are one billion light years apart. Then a few billion years later while located at the same coordinates, we re-determine their distances and find that they are now 3 billion light years apart. The Gaussian coordinates of the galaxies have not changed, nevertheless, their separations have increased. In fact, when the universe was only one year old, the separations between these galaxies were increasing at 300 times the speed of light.</p><p>It is not a motion THROUGH space because the coordinates of the galaxies do not change, instead it is a motion OF space. This is why some popularizers like to use the expanding balloon or raisin bread analogy. It is not the raisins or spots on the balloon that move, but the stretching of the dough or rubber membrane that causes separations to increase. What general relativity proposes, and the balloon analogy attempts to show, is that all of 3-D space at a given instant in cosmic time is contained within a larger object: the 4-D spacetime manifold. This manifold may be sliced along a defined time axis to form 3-D, spatial cross sections. Each of these cross sections represents all of the physical 3-D space that constitutes the universe at any particular instant in Cosmic time. </p><p>If we were to look at two adjacent cross sections through the manifold, they would be represented by a volume of space seen at two different times, but in which one is larger than the other due to the expansion of the universe. If we were to represent the locations of the galaxies in such a space with Gaussian coordinate addresses ( pure numbers) then those addresses would remain the same, but because of the expansion, their physical separations measured, say, by the length of a ray of light, would be different between the two time intervals. The increase in their separations has occurred, not because they moved in the Newtonian sense of changing their coordinates, but because the volume of space in the universe has increased.</p> <p><a href='http://www.eofcosmos.org/article/Universe~_Expansion'>Read Full Article...</a></p> http://www.eofcosmos.org/article/Universe~_Expansion Fri, 02 May 2008 19:47:25 GMT Universe: Creation http://www.eofcosmos.org/article/Universe~_Creation <p>Edwin Schroedinger, by 1939, believed that quantum mechanics itself required that the universe had to be closed because only then would wave functions act discontinuously. Recall that in the Bohr-Heisenberg atom, the orbit that each electron takes around the nucleus is the path for which exactly an integer number of wavelengths of the electron wave function can be accommodated around the orbit's circumference. This leads to discrete states within the atom. Schroedinger believed that the same must be true of the universe. Its closed geometry acted to provide a finite spatial extent within which discrete quantum states would be possible. By studying what happens to the wave function of an electron in an expanding, closed universe, Schroedinger uncovered what he described as an exciting result. The vibrations can be decomposed into two waves traveling the universe in opposite directions, but </p><p> <em>..."if in a certain moment only one of them is present, the </em><em>other one can turn up in the course of time. This is a phenomenon of </em><em>outstanding importance. With particles it would mean production or </em><em>annihilation of matter, merely by the expansion [of the universe]. Alarmed </em><em>by these prospects, I have investigated the question in more detail..."</em></p><p>His resulting calculations contained in some 45 equations, showed that the creation of matter could not occur in this way if the universe were expanding at constant velocity...as it is today...but is only likely when there is rapid acceleration as was likely during the first few moments after the Big Bang. </p><p>In 1953, Bryce DeWitt presented a paper at the American Physical Society meeting in Cambridge Massachusetts entitled "<u>Pair Production by a Curved Metric".</u> He described how in a universe that has a perfectly flat spacetime geometry, small-scale curvature changes can cause pair production in a scalar field. Even if the only field existing in such a universe is the single scalar field, the quantum fluctuations that always occur in any field will interact with the local curvature changes in the spacetime and stimulate the creation of particle-antiparticle pairs. </p><p>The production of matter out of rapidly changing spacetime fluctuations was also explored some years later by Andre Sakharov and by Leonard Parker in 1968-9. Beginning with a small number of fundamental particles in an expanding spacetime, new particles are stimulated into existence out of the quantum fluctuations in the seed particle fields. The number of particles increases as the expansion continues, however, the reaction of the created particles back upon the expansion causes the expansion to slow. This then reduces the production rate of new particles. This process produces equal amounts of matter and antimatter. The current rate of production is about one Pi Meson in a volume as large as the entire observable universe but <em>"...conceivably it was much higher near the start of the Friedman expansion"</em></p><p>By 1972 the scant literature on the physical conditions in the early history of the universe focussed on the problem of the initial Singularity, whether it was avoidable, and what implications it held for the emergence of structure in the universe. No one seriously considered it possible to speak intelligently about what might have preceded the Big Bang.</p> <p><a href='http://www.eofcosmos.org/article/Universe~_Creation'>Read Full Article...</a></p> http://www.eofcosmos.org/article/Universe~_Creation Fri, 02 May 2008 19:46:41 GMT Chandra X-ray Observatory http://www.eofcosmos.org/article/Chandra_X-ray_Observatory <p>Launched with the Shuttle <em>Columbia</em> on July 23 1999 from CapeCanaveral, the <em>Chandra X-ray Observatory </em>is the first X-ray astronomy telescope that matches the /12 arcsecond imaging power, and the 0.1% spectral resolving power, of optical telescopes. (The previous best X-ray telescopes managed <em>either</em> 5 arcseconds [ROSAT],<em> or</em> 10% spectral resolution [ASCA].) Chandra achieves these improved characteristics through much improved X-ray mirrors. These mirrors are 'Wolter type I' mirrors, which reflect X-rays by having the X-rays come in at an angle of only 1 degree to the surface, hence the name 'grazing incidence' mirrors. A Wolter I mirror resembles a slightly tapered cylinder, with a slight parabolic curvature that reflects the X-ray light onto a second, hyperbolic, curve to form an image. Because the X-rays are only bent by a few degrees, the focus lies far from the mirror, 10 meters in the case of <em>Chandra</em>.<br /><br />The fine angular resolution of the <em>Chandra</em> mirror images away the bright background glow of X-rays that had limited the sensitivity of earlier X-ray telescopes, enabling the detection of X-ray sources some 100 times fainter than before. In addition, many X-ray sources, such as supernova remnants and the hot gas in clusters of galaxies, are extended on the sky, and Chandra reveals their structure in great detail. The third advantage of a fine mirror, is that when the transmission gratings are used to disperse the X-rays into a spectrum, much finer detail can be seen.<br /><br />Some major discoveries of Chandra are: *the bulk of the X-ray background is made up of quasars, and almost all the rest is made up of faint galaxies; *quasars repeatedly blow giant bubbles in the hot gas of clusters of galaxies, heating the gas and preventing it from condensing onto the quasar, so shutting off the quasar in a thermostat-like 'feedback'; *tenatively, the space between the galaxies in the nearby universe is filled with hot tenuous gas which, when added up, contains more matter than all the stars and galaxies; pulsars are surrounded by winds of magnetized gas moving close to the speed of light; an unknown region around the black hole at the center of our Milky Way galaxy emits strong bursts of X-rays every day; comets glow in X-rays because of bombardment by the solar wind. Many more examples are given on the Chandra web site.<br /><br />Official public web site: <a href="http://chandra.harvard.edu/" class='external free' title="http://chandra.harvard.edu/">http://chandra.harvard.edu/</a><br /><br /><u>Main Characteristics:</u><br /><em>Operating: </em>23 July 1999 - present (March 2008). Could last through 2020.<br /><em>Band:</em> 0.1-10kilovolt X-rays<br /><em>Angular resolution:</em> 0.5 arcsec<br /><em>Spectral resolving power, R</em>: 10 (ACIS CCDs); ~300 (HETGS, LETGS)<br /><em>Instruments: </em><br />* X-ray mirror (1000 cm^2), 0.5 arcsecond Half Power Diameter (on-axis);<br />* X-ray diffraction gratings, 2: High Spectrometer (HETGS); Low Energy<br />Transmission Grating Spectrometer (LETGS);<br />* CCD imagers: Advanced CCD Imaging Spectrometer (ACIS);<br />* microchannel plate imager: High Resolution Camera (HRC);<br />* star tracker;<br />* particle detector: Electron Proton Helium Instrument (EPHIN). </p> <p><a href='http://www.eofcosmos.org/article/Chandra_X-ray_Observatory'>Read Full Article...</a></p> http://www.eofcosmos.org/article/Chandra_X-ray_Observatory Tue, 15 Apr 2008 19:34:33 GMT BL Lacertae http://www.eofcosmos.org/article/BL_Lacertae <p> BL Lacertae (BL Lac or S4 2200+420) was known to be variable in the visible part of the electromagnetic spectrum from as early as 1929, and because of its stellar appearance it was originally thought to be a VARIABLE STAR. It is located in the constellation Lacerta, the lizard (RA (J2000) = 22h 02m 43.29s, DEC (J2000) = +42<sup>o</sup> 16’ 39.98”). Observations in the late 1960s showed it to have highly variable radio emission as well.<br /><br /> BL Lac was found to be an extragalactic object with the measurement of its redshift (z = 0.069, based on the detection of very weak emission lines) in the early 1970s. During the same period, it was also understood to be an unusual type of ACTIVE GALACTIC NUCLEUS (AGN). Thus, BL Lacertae is the prototype of the class of AGN known as BL LACERTAE OBJECTS (also called BL Lacs). Collectively with some quasars, such as 3C273 and 3C279, they are known as ‘Blazars’. These objects are characterized as having bright nuclei with strongly polarized optical emission and large variability in all wavelengths. Their nonthermal radio-to-gamma-ray continua are thought to be emitted by a relativistic jet oriented close to the line-of-sight. BL Lac objects make up a small subset of AGNs, with about 350 known at present.<br /><br /> BL Lac is an important member of the class because it is relatively nearby, such that details can be well studied. The galaxy surrounding the active nucleus, or host galaxy, is a giant ELLIPTICAL GALAXY, typical of the host galaxies around other BL Lac objects.<br /><br /> Radio observations show BL Lac to exhibit SUPERLUMINAL MOTION, indicative of material being ejected at relativistic velocities from the nucleus. Observations by the Compton Gamma-Ray Observatory showed BL Lac to be a strong gamma-ray source, together with many other blazers. The rapid variability timescales and high luminosities observed at these energies indicate that the gamma rays are produced in a very compact region of the jet.<br /><br /> The nuclear emission in BL Lac is nonthermal and produces a continuum spectrum consisting of two components. The radio-to-ultraviolet spectrum is produced by synchrotron emission with peak power in the infrared-optical region, while the x-ray-to-gamma-ray spectrum is produced by inverse Compton emission. These two components are present in all BL Lacs objects. <br /><br /> BL Lac objects, as a class, are characterized by optical spectra which are featureless or which have extremely weak lines (less than 5Å equivalent width). This property makes the determination of their distances difficult. BL Lac itself is no exception. In the mid-1990s, however, strong, broad and variable emission lines (e.g. H-alpha, equivalent width = 7.3Å luminosity ~2x10<sup>41</sup> erg cm<sup>-2</sup> s<sup>-1</sup>) appeared in the spectrum of BL Lac. Current thinking is that the lines appear when the variable continuum emission is low. Furthermore, the presence of emission lines indicates the presence of a radiation field external to the jet, which may play an important role in the jet energetics (providing seed photons for the inverse Compton emission responsible for the gamma-rays).<br /><br /><em>Bibliography</em></p><ul><li>Catanese M et al 1997 Detection of gamma rays with E > 100MeV from BL Lacertae Astrophys.J. 480 562-7</li><li>Pesce J E, Falomo R and Treves A 1995 Environmental properties of BL Lac objects Astron.J. 110 1554-63</li></ul><ul><li>Sambruna R M, Ghisellini G, Hooper E, Koolgaard R I, Pesce J E and Urry C M 1999, ASCA and contemporaneous ground-based observations of the BL Lacertae objects 1749+096 and 2200+420 (BL Lac) Astrophys.J. 515 140-52</li><li>Urry C M and Padovani P 1995 Unified schemes for radio-loud active galactic nuclei Publ.Astron.Soc.Pacific 107 803-45</li><li>Vermeulen R C, Ogle P M, Tran H D, Browne I W A, Cohen M H, Readhead A C S, Taylor G B and Goodrich R W 1995 When is BL Lac not a BL Lac? Astrophys.J.Lett. 452 L5-8</li></ul><p> </p> <p><a href='http://www.eofcosmos.org/article/BL_Lacertae'>Read Full Article...</a></p> http://www.eofcosmos.org/article/BL_Lacertae Tue, 15 Apr 2008 19:32:41 GMT Keck Observatory http://www.eofcosmos.org/article/Keck_Observatory <a href='http://www.eofcosmos.org/article/Keck_Observatory'><img border='0' src='/upload/thumb/c/c4/Keck.jpg/300px-Keck.jpg' width='100'/></a> <p>From a remote outpost on the summit of Hawaii's dormant Mauna Kea volcano, astronomers at the W. M. Keck Observatory probe the deepest regions of the Universe with unprecedented power and precision.</p> <p>Their instruments are the twin Keck Telescopes, the world's largest optical and infrared telescopes. Each stands eight stories tall and weighs 300 tons, yet operates with nanometer precision. At the heart of each Keck Telescope is a revolutionary primary mirror. Ten meters in diameter, the mirror is composed of 36 hexagonal segments that work in concert as a single piece of reflective glass.</p> <p>Made possible through grants totaling more than $140 million from the W. M. Keck Foundation, the Observatory is operated by the California Association for Research in Astronomy (CARA), whose Board of Directors includes representatives from the California Institute of Technology and the University of California. In 1996, the National Aeronautics and Space Administration (NASA) joined as a partner in the Observatory. The Keck I telescope began science observations in May 1993; Keck II began in October 1996.</p> <p>Keck's capabilities make full use of Mauna Kea's research potential. Surrounded by thousands of miles of relatively thermally stable ocean, the 13,796-foot Mauna Kea summit has no nearby mountain ranges to roil the upper atmosphere or throw light-reflecting dust into the air. Few city lights pollute its extremely dark skies. For most of the year, the atmosphere above Mauna Kea is clear, calm and dry.</p> <p><a href='http://www.eofcosmos.org/article/Keck_Observatory'>Read Full Article...</a></p> http://www.eofcosmos.org/article/Keck_Observatory Fri, 04 Apr 2008 00:59:03 GMT Kepler Mission http://www.eofcosmos.org/article/Kepler_Mission <a href='http://www.eofcosmos.org/article/Kepler_Mission'><img border='0' src='/upload/thumb/9/9a/KeplerSpacecraft.jpg/300px-KeplerSpacecraft.jpg' width='100'/></a> <h1><strong>Importance of Planet Detection</strong></h1><p>Kepler is NASA's first mission capable of finding Earth-size and smaller planets around other stars.</p><p> </p><p class="body_text"> The centuries-old quest for other worlds like our Earth has been rejuvenated by the intense excitement and popular interest surrounding the discovery of giant planets like Jupiter orbiting stars beyond our solar system. With the exception of the pulsar planets, all of the extrasolar planets detected so far are gas giants, approximately 150 as of 2005. The challenge now is to find terrestrial planets (habitable planets like Earth), which are 30 to 600 times less massive than Jupiter.</p> <p class="body_text">The <em>Kepler Mission, </em>a NASA Discovery mission, is specifically designed to survey our region of the Milky Way galaxy to detect and characterize hundreds of Earth-size and smaller planets in or near the habitable zone. The habitable zone encompasses the distances from a star where liquid water can exist on a planet's surface.</p> <p class="body_text">Results from this mission will allow us to place our solar system within the continuum of planetary systems in the Galaxy.</p> <h1><span class="body_text"><strong>Scientific Objective</strong></span></h1> <p class="body_text"> </span></span></span></span></span></span></span></span></span></span></p><p class="body_text">The scientific objective of the <em>Kepler Mission</em> is to explore the structure and diversity of planetary systems. This is achieved by surveying a large sample of stars to:</p> <ol><li><span class="body_text">Determine the percentage of terrestrial and larger planets there are in or near the habitable zone of a wide variety of stars; </span> </li><li><span class="body_text">Determine the distribution of sizes and shapes of the orbits of these planets; </span> </li><li><span class="body_text">Estimate how many planets there are in multiple-star systems; </span> </li><li><span class="body_text">Determine the variety of orbit sizes and planet reflectivities, sizes, masses and densities of short-period giant planets; </span> </li><li><span class="body_text">Identify additional members of each discovered planetary system using other techniques; and </span> </li><li><span class="body_text">Determine the properties of those stars that harbor planetary systems. </span> </li></ol> <p class="body_text">The <em>Kepler Mission</em> also supports the objectives of future NASA Origins theme missions Space Interferometry Mission (SIM) and Terrestrial Planet Finder (TPF),</p> <ul><li><span class="body_text">By identifying the common stellar characteristics of host stars for future planet searches, </span> </li><li><span class="body_text">By defining the volume of space needed for the search and </span> </li><li><span class="body_text">By allowing SIM to target systems already known to have terrestrial planets.</span></li></ul> <h1><strong>The Transit Method of Detecting Extrasolar Planets:</strong></h1> <p class="body_text">When a planet crosses in front of its star as viewed by an observer, the event is call a transit. Transits by terrestrial planets produce a small change in a star's brightness of about 1/10,000 (100 parts per million, ppm), lasting for 2 to 16 hours. This change must be absolutely periodic if it is caused by a planet. In addition, all transits produced by the same planet must be of the same change in brightness and last the same amount of time, thus providing a highly repeatable signal and robust detection method.</p> <p class="body_text">Once detected, the planet's orbital size can be calculated from the period (how long it takes the planet to orbit once around the star) and the mass of the star using Kepler's Third Law of planetary motion. The size of the planet is found from the depth of the transit (how much the brightness of the star drops) and the size of the star. From the orbital size and the temperature of the star, the planet's characteristic temperature can be calculated. From this the question of whether or not the planet is habitable (not necessarily inhabited) can be answered.</p> <p><a href='http://www.eofcosmos.org/article/Kepler_Mission'>Read Full Article...</a></p> http://www.eofcosmos.org/article/Kepler_Mission Thu, 03 Apr 2008 18:24:16 GMT Spiral Galaxies http://www.eofcosmos.org/article/Spiral_Galaxies <a href='http://www.eofcosmos.org/article/Spiral_Galaxies'><img border='0' src='/upload/thumb/4/48/Tfork.gif/180px-Tfork.gif' width='100'/></a> <p>Spiral galaxies are a subset of galaxies, tracing the late stages of the <a href="http://www.eofcosmos.org/article/Hubble_Tuning_Fork" class='external text' title="http://www.eofcosmos.org/article/Hubble Tuning Fork">Hubble classification</a>. They are defined by their thin disks, thick central bulges, the presence of <a href="http://www.eofcosmos.org/article/Hot_Interstellar_Matter" class='external text' title="http://www.eofcosmos.org/article/Hot Interstellar Matter">spiral arms,</a> and blue colors. </p><p style="margin-bottom: 0in"> </p> <h1><strong>Overview</strong></h1> <br /><ul><li>Spiral galaxies constitute ¾ of the total population of galaxies in the field. This fraction changes both with redshift and the local environment density (see <a href="http://www.eofcosmos.org/article/Galaxies~_Morphology-Density_Relation" class='external text' title="http://www.eofcosmos.org/article/Galaxies~ Morphology-Density Relation">Morphology-Density Relation</a>)</li><li>Typical lengths: ~ 1-50 kpc</li><li>Masses: 10<sup>9</sup> – 10<sup>12</sup> solar masses</li><li>Star formation rates: ~1-5 solar masses/year</li><li>M<sub>V</sub> ~ -16 to -23</li><li>Peak rotational velocities: ~ 150-300 km/s</li><li>They exhibit both old and young stellar populations</li><li>They are composed of both dynamically cold and hot stars. The former follow elliptical or near-circular orbits in the disk with little random motions, while the latter follow more chaotic orbits with high dispersions in the bulge.</li><li>Most spiral arms trail the galaxy's direction of rotation.</li><li>More luminous galaxies have higher rotational velocities; this is the basis of the <a href="http://www.eofcosmos.org/article/Tully-Fischer_Relation" class='external text' title="http://www.eofcosmos.org/article/Tully-Fischer Relation">Tully-Fischer</a> relation</li></ul> <h1><strong>Basic Components of Spiral Galaxies:</strong></h1> <ul><li><span><strong>Disk</strong></span><span><span>: The disk contains metal-rich stars and ample <a href="http://www.eofcosmos.org/article/Interstellar_Medium" class='external text' title="http://www.eofcosmos.org/article/Interstellar Medium">interstellar medium</a> (ISM); disk components are generally dynamically cold. Disks are also sites of spiral arms and their <a href="http://www.eofcosmos.org/article/Triggered_Star_Formation" class='external text' title="http://www.eofcosmos.org/article/Triggered Star Formation">triggered star formation</a> regions. Consequently, spiral arms are especially prominent when viewed in blue and ultraviolet light, which characteristic of the arms' younger, luminous stellar populations. </span></span></li><li><span><strong>Bulge</strong></span><span><span>: The central bulge is composed of metal-poor to extremely metal-rich, dynamically hot stars.</span></span></li><li><span><strong>Bar</strong></span><span><span>: These flat, linear structures of stars and ISM are present in about 50% of spiral galaxies. They tend to be as thick as the disk, and have length/width ratios on the order of 5:1. Additionally, bar endpoints can be low-shear environments where triggered star formation may also occur.</span></span></li><li><span><strong>Nucleus</strong></span><span><span>: Nuclei are the innermost, most dense regions of spiral galaxies; they are thought to contain supermassive black holes or intense starbursting regions at their very centers.</span></span></li><li><span><strong>Halo</strong></span><span><span>: The low density environment surrounding the galactic disk, halos contain metal-poor stars, globular clusters, and hot, low density ISM.</span></span></li><li><span><strong>Dark Matter Halo:</strong></span><span><span> The dark halo extends far beyond the visible extent of the galaxy, providing most of the galaxy's mass and controlling its dynamics. We have yet to understand the fundamental composition of this material</span></span></li></ul><br /><ul> <h1><strong>Trends in Spiral Galaxies</strong></h1></ul><p>While there are really no arms to speak of in the S0 systems, we notice that spiral arms tend to wrap themselves tighter as the Hubble classification proceeds from Sa to Sm. This is no surprise; Hubble based his classification scheme on this phenomenon. Furthermore, systems with an abundance of gas are more likely to develop the flocculent structures (as in NGC 2841) resulting from previous generations of supernovae pushing bubbles of star-forming material outward into the ISM for the next cycle of star birth. Otherwise, the trend compliments a generally increasing supply of gas and dust from Sa to Sm.</p><p>Moreover, galaxies tend to get bluer and fainter as they progress from early type to late type spiral. This has much to do with mass and stellar composition; early types are the most massive, showing absorption lines indicative of cooler K and M stars, while the late types are smaller, and display H and K lines of ionized Calcium, among other spectral and photometric indicators of young, blue stars, especially in the active spiral regions.</p><ul> <h1><strong>Rotation Curves and Dark Matter</strong> </h1></ul><p style="margin-bottom: 0in">Thanks to the <a href="http://www.eofcosmos.org/article/Virial_Theorem" class='external text' title="http://www.eofcosmos.org/article/Virial Theorem">Virial Theorem</a>, if we can measure an object’s rotational velocity while knowing its radius, we have a measure of the mass internal to that particular radius. In the case of spiral galaxies, we find that this velocity is constant (past a certain distance) as the radius of the galaxy increases, so the mass internal to that radius must also increase. This inferred mass exceeds what we directly observe by as much as an order of magnitude in some galaxies. This unobserved, yet necessary, mass may be provided by <a href="http://www." class='external text' title="http://www."></font></font></font></font></font></font><font color="#000000"><font color="#000000"><font color="#000000"><font color="#000000"><font color="#000000"><font size="3">eofcosmos.org/article/Dark_Matter</font></font></font></font></font></font><font color="#000000"><font color="#000000"><font color="#000000"><font color="#000000"><font color="#000000"><font size="3"> dark matter</a>.</p> <br />In practice, astronomers obtain a rotation curve by either observing the motions of HI (neutral hydrogen) or CO (carbon monoxide) gas at their characteristic radio emission lines out to a galaxy's edge. We can model a so-called <a href="http://www.eofcosmos.org/article/Spider_Diagram" class='external text' title="http://www.eofcosmos.org/article/Spider Diagram">spider diagram</a>, whose velocity contours are close to those measured in HI or CO and thereby obtain a galaxy's velocity as a function of radius as well as its inclination. This provides a measure of the total mass of the system.<ul> <h1>Further Reading</h1></ul><ul><li>Binney, James, and Merrifield, Michael, 1998. Galactic Astronomy. Princeton University Press, Princeton, NJ, 796 pp.</li><li><a href="http://hubblesite.org" class='external text' title="http://hubblesite.org">HUBBLESITE</a>. 2008</li><li>Gronwall, Caryl, 2008. Galaxies - 2: Spirals. Penn State Astronomy and Astrophysics, State College, PA.<br /></li><li>Sparke, Linda, S., Gallagher, John S. Galaxies in the Universe, 2005. Cambridge University Press, New York, NY, 379 pp.</li></ul><ul><br /></ul> <p><a href='http://www.eofcosmos.org/article/Spiral_Galaxies'>Read Full Article...</a></p> http://www.eofcosmos.org/article/Spiral_Galaxies Mon, 31 Mar 2008 18:47:41 GMT Locke Moon Hoax http://www.eofcosmos.org/article/Locke_Moon_Hoax <p><span style="font-size: 12pt">During the late 1700s and early 1800s, it was widely believed that the Moon was habitable, and even inhabited by “lunarians,” or “selenites.”<span> </span>This view was popularized in the sermons and writings of pluralistic theologians such as Reverend Timothy Dwight, president of Yale College from 1795 to 1817.<span> </span>The English astronomer William Herschel in 1780 declared it to be an “almost absolute certainty” that the Moon is inhabited.<span> </span>In the 1790s, the German astronomer Johann Schröter reported green fields on the surface of the Moon, and also what he took to be a city.<span> </span>In the 1820s, the German selenographer (lunar map maker) went even further, claiming that he had actually seen men and animals on the Moon’s surface.<span> </span></span></p><p><span style="font-size: 12pt"></span><span style="font-size: 12pt">The fascination over lunar inhabitants reached a zenith in 1835, when a series of articles in the <em>New York Sun</em> purported describing lunar observations made with telescopes constructed on “an entirely new principle” by Sir John F.W. Herschel (William’s son) from a site at the Cape of Good Hope in South Africa.<span> </span>The articles were allegedly written by a close assistant to Herschel, but in reality they were penned by Richard Adams Locke, a reporter for the <em>Sun</em>.<span> </span>The articles reported that Sir John had seen sheep, pygmy zebra, and even the fabled unicorn roaming the lunar grasslands.<span> </span>But the most extraordinary creatures described were bipedal winged creatures four feet tall and covered with “short and glossy copper-colored hair,” to which Herschel had supposedly assigned the scientific name <em>Verspertilio homo</em>, or manbat. </span></p><p><span style="font-size: 12pt">The articles were extremely popular with readers, and the <em>Sun</em>’s circulation increased to then-record levels. A few days after the series ended, however, Locke admitted his authorship of the articles to another reporter, who then exposed the deception.<span> </span>Many people felt both foolish and angry for having been taken in by these incredible tales, but when word of the hoax reached Sir John in Africa, he is said to have laughed it off and considered the whole matter a pretty good joke.<span> </span>Today, astronomers know that the Moon’s surface is airless, barren, and uninhabited, but the possibility of other habitable worlds still piques the imagination of Earthly dwellers. </span></p> <p><a href='http://www.eofcosmos.org/article/Locke_Moon_Hoax'>Read Full Article...</a></p> http://www.eofcosmos.org/article/Locke_Moon_Hoax Tue, 25 Mar 2008 01:19:11 GMT Galaxies: Morphology-Density Relation http://www.eofcosmos.org/article/Galaxies~_Morphology-Density_Relation <p style="margin: 0in 0in 0pt" class="MsoNormal">The morphology-density relation describes how different types of galaxies tend to be arranged in clusters. In general, bulge-dominated early-type galaxies, Ellipticals and S0s, preferentially inhabit the central, densest areas of galaxy <a href="http://www.eofcosmos.org/atricle/Galaxy_Clusters" class='external text' title="http://www.eofcosmos.org/atricle/Galaxy Clusters">clusters.</a> Meanwhile, disk-dominated late types tend to be scattered in the more sparsely populated regions of these clusters. This relation is valid for wide variations in shape and richness of clusters. However, this correlation of galaxy shape and the environment it inhabits changes as we look back in time, highlighting some important physical mechanisms at work in clusters and painting a richly dynamic tableau of galaxy evolution as a whole.</p> <h1 style="margin: 0in 0in 0pt" class="MsoNormal">In the Local Universe (z ~ 0)</h1><p style="margin: 0in 0in 0pt" class="MsoNormal">In the early 1980s, it was established that the distribution of galaxy morphologies varied smoothly from the densest regions to the outskirts. In counting the numbers of elipticals, S0s, and spiral galaxies, one can expect to find that each of these galaxies respectively comprises roughly 50%, 40%, and 10% of the total population in the innermost part of the clusters. Outside the cluster, ellipticals and S0s each account for 10% of the number of galaxies, while spirals are 80% of this low density environment population. Again, we see this trend regardless of the differences in individual cluster richness.</p> <h1 style="margin: 0in 0in 0pt" class="MsoNormal">At Intermediate Redshift (z ~ 0.5-1)</h1><p style="margin: 0in 0in 0pt" class="MsoNormal">Despite the powerful morphological segregation we observe locally, this relationship does not hold as a function of redshift. While a similar morphology-density relation is present in centrally concentrated, regular clusters at z ~ 0.5 (about 5 billion years in the past), it is nearly absent in more irregular clusters. More importantly, there is a fundamental discrepancy between the overall number of S0s at this distance and the number we observe locally. There appears to be twice as many of these galaxies in clusters today as there were at z ~ 0.5, whose scarcity is accompanied by a proportionate increase in the spiral population. This situation is more exaggerated as we look back to z ~ 1 (8-9 billion years ago), where it becomes difficult to distinguish galaxies by appearance.</p> <h1 style="margin: 0in 0in 0pt" class="MsoNormal">Possible Explanations</h1><p style="margin: 0in 0in 0pt" class="MsoNormal">Clearly, a large-scale transformation of spiral galaxies to S0s must take place between z~1 and z~0, or from around 8-9 billion years ago to the present. The increasing prominence of gas-poor, dynamically relaxed early-types in cluster cores with time is likely a product of external agents that discourage the maintenance of delicate late-type spiral structure. These include full blown galaxy merging, high speed, ephemeral encounters between galaxies (“galaxy harassment”), ram pressure stripping of interstellar gas by the hot, ionized <a href="http://www.eofcosmos.org/article/Intracluster_Medium" class='external text' title="http://www.eofcosmos.org/article/Intracluster Medium">intracluster medium</a> (ICM), and the gravitational stresses of the cluster environment itself. As a whole, these factors favor the eventual extinction of star formation and the appearances characteristic of early-type galaxies. However, the relative importance of all these processes is still uncertain, and individual scenarios admittedly provide some contradictions to observations, as seen below.</p><ul style="margin-top: 0in"><li class="MsoNormal" style="margin: 0in 0in 0pt"> <p><a href='http://www.eofcosmos.org/article/Galaxies~_Morphology-Density_Relation'>Read Full Article...</a></p> http://www.eofcosmos.org/article/Galaxies~_Morphology-Density_Relation Tue, 18 Mar 2008 22:10:14 GMT Copernicus, Nicolaus http://www.eofcosmos.org/article/Copernicus,_Nicolaus <a href='http://www.eofcosmos.org/article/Copernicus,_Nicolaus'><img border='0' src='/upload/thumb/2/28/Copernicus.jpg/200px-Copernicus.jpg' width='100'/></a> <p>Nicolaus Copernicus (the Latin version of Koppernigk) was a Polish church official whose passion was astronomy, and who actually performed some observations. By that time, all sorts of corrections had to be made to fit the motion of the planets to Ptolemy's ideas. Copernicus proposed an alternative theory--that the Earth was a planet orbiting the Sun, and that all planets moved in circles, one inside the other. Mercury and Venus had the smallest circles, smaller than that of the Earth, and therefore their position in the sky was always near the Sun's.</p><p> That made it easy to estimate their distances from the Sun in terms of the Earth-Sun distance. Mars, Jupiter and Saturn moved in bigger circles, and they moved more slowly, so that whenever the Earth overtook them, they seemed to move backwards.</p><p>Copernicus was quite cautious in voicing his theory: not only did it deny that the Earth was the center of the universe, but it, too, did not fully describe the motion of the planets. Some corrections were still needed. Being associated with the church (as practically all European scholars were in those days), Copernicus had to abide by a rigid discipline, and he therefore hedged his ideas and only published them at the end of his life. Because of his caution, many church scholars indeed viewed his theory as a possible alternative to Ptolemy's.</p><p>His epochal book, <em>De revolutionibus orbium coelestium</em> (<em>On the Revolutions of the Celestial Spheres</em>), is regarded as the starting point of modern astronomy. </p> <p><a href='http://www.eofcosmos.org/article/Copernicus,_Nicolaus'>Read Full Article...</a></p> http://www.eofcosmos.org/article/Copernicus,_Nicolaus Wed, 05 Mar 2008 06:17:45 GMT