Monday, December 24, 2007


So remote are the stars that their distances are measured not in kilometres or miles but in the time that light takes to travel from them to us. Light has the fastest speed in the Universe, 300,000 sec (l86,000 mile). It takes just over 1 second to cross the gap from the Moon to the Earth, 8.3 minutes to reach us from the Sun, and 4.3 years to reach the Earth from the nearest star. Alpha Centauri. Hence Alpha Centauri is 4.3 years away.

Most of the stars visible to the naked eye lie from dozons to hundreds of light years away. It is hard to think that the light entering our eyes at night left those stars so long ago. The most distant stars that can be seen by the naked eye are over 1000 light years away, for example Deneb in the constellation Cygnus and several of the stars in Orion. Only the most luminous stars, those that blaze more brightly than 50,000 Suns, are visible to the naked eye over such great distances. At the other end of the scale, the feeblest stars emit less than a thousandth the light of the Sun, and even the closest of them cannot be seen without a telescope