|Sunday, 5 December 2004|
Constellations are clusters of stars
On a really dark night, you will see about 1000 to 1500 stars. But you will find it difficult to tell which is which. Don't worry, with the help of constellations, which break up the sky into more manageable parts, you will be able to identify many stars.
The constellations are totally imaginary things that poets, farmers and astronomers have made up over the years.
In total there are about 88 constellations, which have been divided into eight constellation families.
We use constellations to divide the sky. By finding one constellation, we can find another because constellations move so slowly that, in our lifetime, they will always be found in about the same place.
Many names we use today for constellations came from the ancient Greeks. They used to assign their gods and heroes to certain figures in the sky, which they formed using clusters of stars. But due to their northern location they only gave names to those regions visible from their countries.
No one knows when mankind started giving names to stars and grouping stars. It is most likely that constellation names were invented by early sailors for navigation purposes. In the deserts too they may have been of help for people to find their way.
Therefore it is quite natural that each culture grouped the stars differently and gave them names from their natural and social environment.The twelve constellations of the zodiac we know today date back to the time of Babylonians and Chaldeans who lived about 2000 to 3000 years ago. Back then, it was believed that the sun passed through the twelve constellations we assign to the zodiac.
The best known group of stars is the Big Dipper; you have probably heard of it or even seen it. The Big Dipper is a group of seven bright stars, three which form a handle and four which form a bowl. The Big Dipper is not actually a constellation but is part of the constellation Ursa Major or Great Bear.
Another well-known constellation is Orion. Orion was an ancient Greek hunter and warrior and the constellation resembles this figure with a club and a shield and a sword dangling from his belt. The belt is the easiest part of the Orion to spot, with three bright stars in a row. Orion has more bright stars than any other constellation.
The Pleiades or the Seven Sisters were said to be the daughters of Atlas and the objects of Orion's affection. As the name Seven Sisters implies, there are seven stars in this constellation but most people can only see six. The Pleiades is located between the constellations of Taurus and Perseus.
The study of gamma-ray bursts
The Swift is a first-of-its-kind, multi-wavelength observatory dedicated to the study of gamma-ray burst (GRB) science. During its nominal two year mission, Swift is expected to observe more than 200 bursts, which will represent the most comprehensive study of GRB afterglow to date.
The satellite and Swift mission is a collaboration between laboratories and universities in the USA, England and Italy.
What are black holes?
The grave of a massive star is called a black hole and one such black hole identified by astronomers is Cygnus X-1.
How does it happen? If a shrunken core left behind by a supernova has a mass of more than three Suns, its gravitational pull is so strong that nothing escapes, not even the star's own light. The object becomes invisible and it is a black hole.
A black hole can swallow up gas and even passing stars. Gas falling into a black hole heats up millions of degrees, at which temperature it emits X-rays which can be detected by satellites orbiting the Earth.
Astronomers believe that large black holes, containing the mass of millions of Suns, are lying in the heart of galaxies.
Produced by Lake House