Name: International Year of Astronomy 2009
Date of Issue: 25 May 2009
Country: Faroe Islands
Denominations: DKK 22,00
In 1609, the Italian astronomer and physicist, Galileo Galilei, learned that Hans Lippershey in Holland had performed experiments with a telescope. Galileo immediately began his own experiments with lenses. After a short time, he had built his own telescope. He understood that the telescope could be a useful instrument for exploring space. One November evening in 1609, he saw both deep craters and flat plains on the Moon. On the nights following, he looked at different constellations and discovered that he could see many more stars using his telescope than with the naked eye. He also discovered that the Milky Way was nothing less than a collection of an inconceivable number of stars.
On 7 January 1610, he observed Jupiter through his telescope. He saw three small ‘stars’ close to Jupiter, two on the western side of the planet and one on the eastern side of the planet. At first, he believed them to be fixed stars and he followed these stars on subsequent nights. On 13 January, he wrote in his journal that he could now see a fourth star near Jupiter. On the 14th, the sky was overcast, but on the 15th the skies were clear again and all four stars were now west of the planet. The mystery was now solved: The ‘stars’ were actually moons in orbit around Jupiter. These four moons are now jointly called the Galilean moons. This reinforced Galileo’s Copernican conviction that the Sun was the centre of the solar system. If moons can orbit Jupiter, the Earth and the other planets could also orbit the Sun. Galileo also observed Saturn, but could not distinguish its rings. His telescope was not advanced enough. He drew Saturn as three celestial bodies in a line.