Introduction to Constellations
'Constellation' is the name we give to seeming patterns of starsin the night sky. 'Stella' is the Latin word for star and a constellation is a grouping of stars. In general, the stars in these groups are not actually close to each other in space, they just appear to be close when viewed from Earth. If we could travel by spaceship to another part of the galaxy, we would imagine an entirely different set of constellations. In the meantime, for us on Earth, the constellations are a handy way to locate a star in the sky. On Earth, we see different constellations as we travel to different parts of the globe. The fact that some constellations were visible in the northern hemisphere and not the southern hemisphere, and vice-versa, was used more than 2000 years ago by Greek astronomers to argue that the Earth is round.
Long before the invention of the telescope, early civilizations invented star patterns and named them after animals, objects, heroes, gods, and beasts from stories and myths. Many of these myths were probably created to explain changes in the sky due to seasons, etc. The ancient Greeks named many constellations. For example, they told the story of Orion, the hunter, who leaped into the sea to escape a scorpion's bite, which explained why the constellation Orion disappears from the sky when the constellation Scorpius rises. Different civilizations imagined different patterns, and some stars were included in more than one pattern. Over time, the situation became confusing.
In 1929 the International Astronomical Union defined 88 constellations that are today recognized as the 'official' constellations. Many of these constellations are derived from the complex creations of Greek mythology, like Andromeda, Perseus, and Orion. Others came from ancient cultures such as the Egyptians and Chaldeans and still others were not defined until the 17th and 18th century. In the past, people used the constellations as markers. Some used the constellations to navigate their boats across the sea, to mark seasons of the year, or to locate special stars. Today, astronomers still use constellations as a handy marker to indicate a general area of the sky where far away celestial objects appear. Many of these extremely distant objects can be seen only with powerful telescopes.
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Chandra X-Ray Observatory Center
The Chandra X-ray Observatory, previously known as the Advanced X-ray Astrophysics Facility, is a Flagship-class space telescope launched aboard the Space Shuttle Columbia during STS-93 by NASA on July 23, 1999.