Astronomical Information Center
Glossary of Terms
Phenomena of the Sun and Moon
- Rise, Set, and Twilight Definitions
- Lengths of Longest and Shortest Days
- Length of Day and Night at the Equinoxes
- The Dark Days of Winter
- Visibility of the Crescent Moon
- References on Eclipses
- Phases of the Moon and Percent of the Moon Illuminated
Time
- Universal Time and Greenwich Mean Time
- Computing Greenwich Apparent Sidereal Time
- What are the U.S. Time Zones?
- World Time Zone Map
- When Does Daylight Time Begin and End?
Calendars and Historical Events
- Introduction to Calendars
- Leap Years
- U.S. Holidays
- The International Date Line
- The 21st Century and the 3rd Millennium
- The First Sunrise of the New Millennium
Computing Astronomical Data and Phenomena
- Converting Between Julian Dates and Gregorian Calendar Dates
- Computing Times of Rise and Set
- Approximate Solar Coordinates
- Computing Greenwich Apparent Sidereal Time
- Computing Altitude and Azimuth
Other Topics
- Astronomical Data Used for Litigation
- Celestial Navigation Resources
- The Seasons and the Earth's Orbit
- Variation in Times of Perihelion and Aphelion
- International Celestial Reference System (ICRS)
- When Did the Asteroids Become Minor Planets?
Links to Information at Other Sites
- "Explaining The Moon Illusion" - why the Moon looks larger close to the horizon (by Lloyd Kaufman and James Kaufman for the Proceedings of the National Academy of Sciences)
- What is a Blue Moon? (by David Harper)
- An Introduction to Green Flashes (by Andrew T. Young, San Diego State University)
- Photographs of an Inferior-Mirage Sunset - strange Sun shapes near the horizon and related phenomena (by Andrew T. Young, San Diego State University)
- Sunspots and Solar Activity
- Weather and Climate
- Sky conditions for astronomical observing
- Tides
- Maps
