This issue is also available as a digital download.

The most basic device for recording and predicting the motions of astronomical bodies is the calendar. It helps us track Earth’s rotation and its motion around the Sun, and the Moon’s orbit around Earth. The modern western calendar has been revised and tweaked over the centuries, but it’s still the same basic system in use in the days of Julius Caesar. Our almanac explains the history and operation of the calendar, and offers glimpses into other calendar systems, including the Mayan Long Count.

Our 2010 Sky Almanac is 32 full-color pages of monthly skywatching tips, charts and photos, astronomical anniversaries, and space-mission information. We also bring you information on events you can attend across the nation. The theme for this year's Sky Almanac is the calendar, the most basic device for recording and predicting the motions of astronomical bodies. Learn the history and operations of our Western calendar, and others.

Sky Almanac 1999-2009

More Stargazing Information

Consult these pages for updated information on stargazing events throughout the year:

• Weekly tips
• Meteor showers
• Planet viewing