Four hundred years ago Galileo Galilei of
took a new technological device and directed it to the sky. In the summer, fall and winter of 1609, he undertook careful telescopic studies of the planets, the Moon and the stars. In the spring of 1610 he published a book describing his discoveries.

In SideriusNuncius, he stated that the Moon has mountains just as the Earth, that the Milky Way was not a diffuse cloud of brightness but composed of faint individual stars, and that the planet Jupiter had its own set of regularly orbiting moons.

Galileo’s book revealed the unknown; he drew conclusions from his own observations even though those conclusions flew in the face of centuries of strongly held beliefs to the contrary. Its publication sparked others to build their own telescopes and turn them toward the heavens. The man who set physics on its way by making laboratory measurements of objects in motion jump-started modern astronomy with a new technological device and an open mind that gave precedence to observation over prevailing dogma.

To commemorate Galileo’s seminal telescopic discoveries 400 years ago and the contribution of astronomy to understanding the universe and our place in it, UNESCO and the United Nations have officially proclaimed 2009 to be the International Year of Astronomy (IYA). In addition, a resolution, H.R. 375, has been introduced in the U.S. House of Representatives by Rep. Gabrielle Giffords (D-Ariz.) recognizing the importance of the year, which is also the 40th anniversary of the first Apollo lunar landing, another seminal milestone in human history.

The International Astronomical Union (IAU) is coordinating worldwide projects devoted to bringing science and discovery to citizens of all nations during the IYA. Already, 118 countries and more than 40 organizations are working together to carry out a wide range of activities from the development of a high-quality, low-cost telescope kit with educational activities on optics and astronomy to be made available worldwide, to an easily reproduced astronomical image exhibition suitable for shopping malls, airports, science centers and museums. The projects cover a huge spectrum of topics, ages and interests.

More than just a yearlong celebration, IYA is working to encourage all people to rediscover their place in the universe through the day- and nighttime sky, and thereby engage a personal sense of discovery and awareness. We are attempting to reach the majority of citizens of this planet so that they will be able to relate to the cosmos in a meaningful way during 2009.

The ever-developing Web site presents IYA activities in the
United States
and allows an entry point for those who want to participate or help. As the year approaches, this site will allow users in the
United States
to find an activity and connect to others interested in astronomy in their area. Given the projects proposed and the energy and excitement so clearly evident among those planning for the IYA, we in the IAU and American Astronomical Society are confident of its success. Needless to say, funds are needed and are being actively sought.

We urge the space science community to find ways to support the IYA directly. Fundamentally, space astronomy, planetary science and heliophysics are the great-grandchildren of the initial studies carried out by Galileo. These fields represent humankind’s ongoing quest to understand our place in the universe, how we came to be, and how the universe will change over time.

We understand much more today than we did in 1609, but the struggle between unexpected observation and belief goes on within all of us as our quest for knowledge uncovers apparent contradictions along with answers. The satellites, probes and landers developed by the space industry enable this quest. We all work together to increase human understanding by exploring the unknown with human-built machines launched into space on human-built rockets. We value your participation in working with us to celebrate astronomy and its important bases, technology and the scientific process, during the International Year of Astronomy 2009.

Robert Williams is president-elect of the International Astronomical Union and former director of the Space Telescope Science Institute. Kevin Marvel is executive officer of the American Astronomical Society.