Happy New Year, and thanks for checking out the first edition of Night Skies for 2009, the International Year of Astronomy. On this day in 1610, Galileo observed Jupiter with his telescope and discovered its moons Io, Europa and Callisto.

Galileo was a maverick of his time. As a military engineer and mathematician, he was well-versed in pragmatic methodology. In the early 17th century, the understanding of our world was largely anchored in Aristotle's geocentric model. Aristotle proposed that our planet was made of four elements water, earth, wind and fire. The interaction of these elements were responsible for everything we could see in nature — the growth and blossom on a flower, fire burning a log into ash, water eroding a hillside. Our natural world was seen as mutable and imperfect.

In this world view, heavenly bodies were made of a fifth element not found on our world — aether. Aether was stable and pure. Distant objects like the moon, stars or planets were believed to have smooth, perfect surfaces and move in circles about the Earth. But, anybody with a lick of sense could look up and see that the moon appears irregular and rugged. Grumblings about this contradiction to Aristotle's model of celestial purity began in the Middle Ages. How something not of Earth could appear imperfect was a hotly contested issue. To quell dissenters, some scholars floated the idea that the rugged surface of the moon was actually encased within a transparent sphere of aether.

Galileo would have none of it. The Scientific Method of Ibn al-Haytham and Francis Bacon was at the core of Galileo's study of the natural world. He was interested in testing hypotheses against reality not through a process of deductive reasoning or philosophy. While observing the moon, he noted that mountain peaks and crater rims became illuminated by the lunar dawn well before basins and lowlands. This shadow play was analogous to what he had seen here on Earth. Mountaintops catch sun light before the foothills. His careful sketches and logged observations allowed Galileo to systematically uncover the truth.

After the moon and Jupiter's satellites, he turned his telescope to Venus, Saturn and the sun. By studying the phases of Venus, Galileo was able to confirm the Copernican theory that the sun was at the center of our solar system.

Galileo's work provided the foundation for the modern science of astronomy and sparked a fundamental shift in how we explore and understand the universe around us.

To learn more about the International Year of Astronomy, visit online at www.astronomy2009.com. There you will find information and links to all kinds of resources including a daily podcast at www.365daysofastronomy.org.



Peter Lipscomb is director of the Night Sky Program for the New Mexico Heritage Preservation Alliance. Contact him at plipscomb@nmheritage.org