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  The science of astronomy (Greek, ‘naming the stars’) was born when man began to observe and track the motion of the stars in the night sky. Initially, it was naturally assumed that the stars, Sun and Moon all circled the Earth. However, the behaviour of the planets, which appear as bright star-like objects moving against a background of fixed stars, does not fit this picture very well, and new explanations were sought.

Copernicus (Nikolaus Koppernigk (1473 - 1543) was the first to realize that the motion of the planets can be explained if one considers them to be orbiting the Sun with the Earth, thus showing that the Sun is the centre of the solar system and demoting the Earth to satellite status. , Johannes Kepler (1571 - 1630) described the system more fully, showing that they move not in circles but in ellipses with the Sun at one of the foci of the ellipse. This motion was shown to be a consequence of the nature of gravity by Newton.

Since Newton\'s time astronomy has increased in sophistication. Early telescopes observed only the visible light from the sky. Visible light, however, is only one small part of the electromagnetic spectrum, and today we utilize far more of it, from radio waves and microwaves to the ultra-violet and x-ray regions. Our atmosphere is an obstacle to observation; as well as confusing observations by shimmer, or blurring, it also attenuates all frequencies other than visible and radio waves. Thus many observatories are built in high places, where there is less atmosphere. This enables visible light to be detected with less distortion, and other frequencies to arrive at the telescope with greater intensity. Computers and electronics have revolutionized astronomy, greatly reducing the time needed to track and analyse objects.

Telescopes differ widely, depending upon the type of radiation that they are designed to detect. Radio telescopes are huge metal dishes, which need to be large because radio waves have wavelengths of the order of a metre. Light telescopes require mirrors and lenses of high quality; a mirror for a good telescope must be smooth enough that irregularities upon its surface are smaller than the wavelength of light, which is about one thousandth of a millimetre. Microwave dishes are typically a few metres across. The quest to observe the sky in other wavelengths has led to suggestions for space telescopes which would eliminate atmospheric distortion.

Astronomical observations reveal a wealth of information about the universe. From them we may learn about the early life of the universe, the evolution of stars and galaxies and the existence of bizarre objects like neutron stars and black holes. Because it is electromagnetic radiation, which travels at the speed of light, which we observe, the further an object is, the earlier in its history we are seeing it. If the light from a star takes 1,000 years to reach the Earth, then what we see is a picture of the star 1,000 years ago, not the star as it is today—it may not even exist at this time! Thus to see what the early universe was like, we look at very distant objects. JJ



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