The International Year of Astronomy 2009

Galileo

The year 2009 has been designated The International Year of Astronomy to celebrate the first astronomical use of the telescope by Galileo Galilei – a momentous event that initiated 400 years of astronomical discoveries and triggered a scientific revolution which profoundly affected our world view. As he wrote in Starry Messenger, "all the disputes which have tormented philosophers through so many ages are exploded at once by the irrefragable evidence of our eyes." He saw that the moon was not a perfect celestial body but had mountains on it; he went on to find that Jupiter had moons and he observed the phases of Venus, direct evidence for Copernican heliocentrism. These discoveries were blows to the Aristotelian/Ptolemaic world-view which was geocentric and maintained that everything above the Earth was perfect and incorruptible. The notorious persecution of Galileo by the Church for his support for Copernicus, resulting in his forced recantation and house arrest, is detailed by Paul Newall. In 1616 the Congregation of the Index had declared that the heliocentric theory was "false and contrary to Holy Scripture". Copernican works remained on the list of forbidden books until 1822 and the Church has been trying to extricate itself from the whole sorry affair ever since – "The greatness of Galileo is known to everyone … [He] had to suffer a great deal – we cannot conceal the fact – at the hands of men and organisms of the Church." (Pope John Paul II in 1979). Annibale Fantoli in Galileo: For Copernicanism and for the Church (Vatican Observatory Foundation, 1996) comments:

[The Galileo Affair] remains, and should remain, "open"... as a severe lesson of humility to the Church at all levels and as a warning, no less rigorous, not to wish to repeat in the present or in the near future the errors of the past, even the most recent past.

Amazingly, heliocentrism still seems to be an issue for some. Ptolemy's model was essentially a mathematical system for predicting the positions of the planets as seen from the Earth, but Galileo's observations showed that it was not an adequate description of how the planets move in three-dimensional space. Both Ptolemy and Copernicus assumed that the planets moved on perfect circles and it was left to Kepler to give a more realistic description of planetary orbits. A good description of these problems and the contribution of Islamic astronomy is given by Owen Gingerich in an article for Scientific American (April 1986 v254 p74).

Kepler

1609 also saw the publication of Johannes Kepler's Astronomia nova (A New Astronomy) in which he described the orbits of the planets around the sun as ellipses, a final breakthrough into the scholastic Aristotelian physics and philosophy.

Modern times

2009 sees the 40^th anniversary of the first moon landing on July 20, 1969 by astronauts Neil Armstrong and Buzz Aldrin.

The Kepler telescope, NASA's first mission capable of finding Earth-size and smaller planets around other stars, is due to be launched in 2009.