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Astronomers through time...

ATCA with storm clouds and rainbow - old helioscope in the foreground - image courtesy of - http://www.atnf.csiro.au/imagebank/telescopes.htmlAstronomers over the centuries, through millions of observations, developed ways of using the stars to track seasons, erecting large structures to follow the path of the sun and moon. Finding solar systems, planets and many intriguing formations in the solar system. These provided clocks or calendars to follow the passing of the seasons.

A few of many are listed below with links to several biographies written outlining their achievements in the history books.

Individuals such as Thales studied mathematics and claimed that the Earth was spherical in shape, Pythogoras proposed that the Universe was made of concentric spheres surrounding the Earth, the sun, moon and planets each travelled in their own sphere.

Eudoxos (c400 355BC) taught that the heavens revolved around the earth, which was the centre of the universe but added to Pythogorian system by adding more spheres to account for the irregular movements of the planets and the moon.

Aristotle showed that the Earth was a sphere but thought that the Earth was the centre of the universe because he couldn't see the stars shift position thru the year. (The stars are too far away to see their movement in a short period of time).

Aristarchus (c 200s BC) held an opposite theory, he showed that certain movements of the sky could be explained by assuming that the earth moved around the sun. The important ideas of early astronomy were developed by Greek scholars during the 400 years before the birth of Christ.

Hipparchus (c 100s BC) carefully recorded the positions of stars, the sun, and the moon. His work was so complete that other astronomers used it to predict eclipses of the sun and the moon. He accurately measured the distance from the Earth to the Moon, completed the first known star catalogue and developed the magnitude system for comparing star brightness. He also discovered precession - the slow wobble of the Earth's axis caused by the gravitational pull of the sun and moon.

About AD 150 Claudius Ptolemy published a book based on the work of Hipparchus. Ptolemy was a Greek astronomer working in Egypt. In his book he strengthened the idea that the earth was the centre of the universe. The book became highly respected, and it firmly established his theory among Greek and Arab astronomers. Gradually, European scholars learned about Ptolemy's work from the Greeks and the Arabs. For more than a thousand years no one seriously questioned Ptolemy's theory.

Nicholas Copernicus (1473 - 1543) was largely responsible for advancing astronomy beyond the ideas of Ptolemy and others. A member of the Church and studying astronomy and mathematics, he was unhappy with the many errors in the system of Ptolemy and decided to revise those ideas by placing the sun at the centre of the Universe with the Earth and other planets orbiting around it.

Tycho Brahe (1546 - 1601) accepted Copernicus ideas and set out to make accurate observations of the skies. Working on the Baltic island of Hven he built an observatory (the Castle of Uraniborg) where he gathered a large amount of accurate observations which led to the development of a model where the planets orbit the sun but the sun orbits a stationary Earth. Tycho's model did not gain wide spread acceptance but an assistant of Tycho's - Johnnes Kepler (1571 - 1630) continued Tycho's work but found great difficulty fitting the orbit of Mars into a circular orbit, he therefore abandoned the circular orbit and substituted the ellipse thereby fitting the observations taken of Mars.

In 1590 a Dutchman - Zacharias Jansen designed the first telescope and in 1608 Jan Lippershey manufactured the first usable telescope. Galileo Galilei (1564 - 1642) modified a Jansen-Lippershey telescope to look at the sky, his discovery of craters and mountains on the moon, the four large satellites of Jupiter, sunspots and phases of Venus, amazed astronomers but due to religious opposition Galileo was placed on trial by the Church and found guilty of teaching Copernican theory. He was forced to renounce his astronomical findings.

Isaac Newton (1642 - 1727) used mathematics to work out planetary motions and developed the theory of universal gravitation - the action of gravity which works throughout the Universe. Newton's model put astronomy on a firm footing making it possible to accurately predict the motion of the planets around the sun.

Astronomer Sir William Herschel (1738 - 1822) constructed a 40 foot long telescope and with it discovered the first of the modern planets Uranus in 1781 as well as about 5,000 nebulae, stars and planetary nebula.

Neptune was discovered in 1846 by Johann Galle (1812 - 1910) as a result of calculations by Urbain Leverrier (1811 - 1877). At the same time John Couch Adams (1819 - 1892) independently also calculated the position of Neptune. Percival Lowell (1855 - 1916) predicted that a planet must exist beyond the orbit of Neptune in 1905

It wasn't until 1930 that C. W Tombaugh working at the Lowell Observatory in Arizona USA discovered the last of the modern planets - Pluto. In 1978 it was discovered that Pluto has a satellite - Charon. Visiting probes and greatly enhanced telescopes continue to find satellites orbiting the large planets far from our sun.