space answer book
How many Seyfert galaxies does the universe contain?
At present more than 150 Seyfert galaxies have been discovered, accounting for roughly 10 percent of all known giant spiral galaxies.
What is the Milky Way galaxy?
The Milky Way is our home galaxy. It contains the sun and billions of other stars. In addition to over one hundred billion stars and possible black holes, the Milky Way is comprised of star clusters, planets, glowing nebulae (gas clouds), dust, and empty space. Older stars and denser clusters lie near the center of the galaxy while younger stars and open clusters reside in the plane of the disk.
What kind of galaxy is the Milky Way?
The Milky Way is a spiral-shaped galaxy, meaning it is shaped like a pinwheel. It is ap-proximately one hundred thousand light-years in diameter and two thousand light-years thick from top to bottom. It has a group of objects at the center (mostly older stars and maybe a black hole), surrounded by a halo (a band of star clusters) and an invisible cloud of dark matter, with four arms spiraling out from the center. The spiral shape is formed because the entire galaxy is rotating, with the stars at the outer edges forming the arms.
How has anti-matter altered our concept of the Milky Way galaxy?
Astrophysicists at the U.S. Naval Research Laboratory, Northwestern University, and the University of California at Berkeley, analyzing data from the Compton Gamma Ray Observatory (CGRO), announced in 1997 that they had discovered an enormous foun-tain of anti-matter spurting upward from the center of the spiral Milky Way galaxy, the galaxy in which Earth's solar system is located. The plume of positrons, 25,000 light-years from Earth, is about 4,000 light-years across and rises 3,500 light-years above our disk-shaped galaxy. While the scientists were not certain of the nature of the anti-matter geyser, they proposed that it might be gas rising from stars exploding in death near the center of the galaxy mixed with a stream of positrons. The fountain emits continuous gamma rays, which were detected by the CGRO. This finding significantly modifies our understanding of the Milky Way galaxy.
Wíthin the Milky Way galaxy, where is our solar system located?
Our solar system is located in one of the Milky Way galaxy's four spiraling arms, called the Orion arm. Our sun, which is a relatively young star, lies about thirty thousand light-years from the center.
Where does the Milky Way galaxy fit in to the rest of the universe?
Galaxies are as plentiful in the universe as grains of sand on the beach. The Milky Way is part of a cluster of galaxies known as the Local Group, and the Local Group is part of a local supercluster that includes many clusters. Superclusters are separated by ex-tremely large voids of space, with very few galaxies in between.
Can we see the Milky Way?
From Earth, we can see only the part of the Milky Way that surrounds us, because so much of the galaxy (particularly near the center) is blocked from view by interstellar dust and gas. It is visible on clear, summer nights, in places far from the glare of city lights.
Why is our galaxy called the Milky Way?
The Milky Way appears as a starry expanse of light stretching across the sky. In ancient times, people felt this glowing band of light resembled a river of milk, which is how it got its ñame.
When did scientists begin to study the Milky Way?
In the early 1600s, Galileo Galilei first examined the Milky Way through a telescope and saw that the glowing band was made up of countless stars. As early as 1755, Germán philosopher Immanuel Kant suggested that the Milky Way was a lens-shaped group of stars, and that many other such groups existed in the universe. Germán astronomer William Herschel (1738-1822), who lived and worked in England, is per-haps best known for his discovery in 1781 of the planet Uranias. Among his many other astronomical accomplishments, Herschel was the first astronomer to conduct a scientific survey of the Milky Way.
When did astronomers begin to determine our location in the galaxy?
Before 1918, astronomers believed that our solar system was at the center of the Milky Way. Then American astronomer Harlow Shapley, after studying the distribution of star clusters in the galaxy, determined that this was not the case.
How do astronomers study the Milky Way today?
Astronomers today use a number of sophisticated methods to examine the Milky Way and other galaxies. Until recently we did not have a picture of our galactic core. The reason is that dense clouds and dust block the visible light. It turns out, however, that radio waves and infrared light shine through these obstacles, and objects can be dis-tinguished by radio and infrared telescopes. Using these specialized instruments we have come closer to answering many questions about our own galaxy and others, including how stars are born and how galaxies are formed.
How big is Andromeda galaxy?
Andromeda galaxy contains hundreds of billions of stars. Some of them are part of the six hundred or so globular clusters located on the edges of the galaxy. Each one of these nearly spherical síar systems contains anywhere from tens of thousands to millions of stars.
Why are astronomers particularly interested in studying the Andromeda galaxy?
Andromeda galaxy shares many characteristics with the Milky Way. It is the same shape and about the same age, contains many of the same types of objects, and, like the Milky Way, is believed to have a black hole at its center. The two galaxies are also the same size, each about one hundred thousand light-years across. The Milky Way and Andromeda are both spiral galaxies. Astronomers continuously study Andromeda, in part seeking clues about our own galaxy. Despite its distance from us, Andromeda is still actually easier to study than the Milky Way. The reason is that from Earth's posi-tion in the middle of the Milky Way, many parts of our own galaxy are blocked from view by dust.
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How accurate is the Gregorian calendar?
The Gregorian calendar, although not perfect, is accurate to within .000301 days (or 26 seconds) per year. At this rate, it will be off by one day every thirty-three hundred years. As we approach the year 2000, we still have nearly two millennia before the extra day catches up with us. This should be ampie time for calendar-makers to find a solution.
How advanced was ancient Chínese astronomy?
Some of the world's earliest astronómica! observations were made by the Chínese. Perhaps as early as 1500 B.C., Chínese astronomers created the first rough charts of the heavens. Then in 613 B.C., they described the sighting of a comet. Within a few centuries Chínese astronomers were keeping track of every eclipse, sunspot, nova, me-teor, and other celestial phenomena they observed. Chínese astronomers made nu-merous contributions to the field. For instance, they studied the question of the Earth's motion and created one of the first calendars. Another feat that distinguished the Chínese from other ancient astronomers was their creation of a primitive map of the celestial sphere, on which they placed stars in relation to the sun and the North Star. Chínese astronomers were also the first to observe the sun by looking through tinted crystal or jade.
By the fourth century B.C., astronomers had produced a number of star charts, which depicted the sky as a hemisphere. This form of mapping is understandable, since we can only see half the sky at any one time. It took three hundred more years for Chi-nese astronomers to regard the heavens as an entire sphere, a sign that they were then aware of the Earth's own spherical shape, as well as of the Earth's rotation about its axis. The Sung dynasty, which began in the year A.D. 960, was a period during which astronomical discoveries were greatly encouraged. Around this time the first astronomical clock was built, and mathematics was first introduced into Chínese astronomy.
What does the Dresden Codex tell us about the sophistication of ancient Mayan astronomy?
The three remaining records from what is believed to have been an extensive Mayan li-brary are books constructed from bark. One of these books is a now-famous work called the "Dresden Codex." The Dresden Codex is so-named because it was discovered in the late 1800s in the archives of a library in Dresden, Germany. It includes observa-tions of the motions of the moon and Venus and predictions of the times at which lunar eclipses would occur. The most remarkable section of the Dresden Codex is a complete record of the orbit of Venus around the sun. Mayan astronomers had cor-rectly calculated that it takes Venus 584 days to complete a revolution. They arrived at this figure by counting the number of days that Venus first appeared in the sky in the morning, then the days when it first appeared in the evening, and finally the days that it was blocked from view because it was on the opposite side of the sun. They marked the beginning and ending of the cycle with the heliacal rising, the day on which Venus rose at the same time as the sun.
What is Stonehenge?
One of the world's most famous ancient astronomical sites is Stonehenge. This com-plex assembly of boulders and ditches is located in the southwest of England, about 8 miles (13 kilometers) from the town of Salisbury. Stonehenge was built and re-built over three periods, most likely between the years 3100 B.C. and 1100 B.C. The archi-tects of this monument were probably ancient druids, an order of Welsh and British priests. While Stonehenge is widely believed to have had some astronomical function, exactly what that function was remains in question.
How cióse to the original structure is the Stonehenge we see today?
The effects of about five thousand years of rain and wind, plus the action of vandals, have significantly altered Stonehenge from its original form. Studies undertaken by archaeologists and anthropologists indícate that at one time it contained thirty blocks of gray sandstone, each standing about 13.5 feet (4.1 meters) high, arranged in a 97-foot-diameter (29-meter-diameter) circle. Lying horizontally on top of these stones and forming a continuous ring were thirty smaller stone slabs. A second, inner circle of stones enclosed a third, horseshoe-shaped group of stones. Today, all remains is a partial outer ring and a handful of inner stones.
