Book excerpt: Prepared jointly with Her Majesty's Nautical Almanac Office, United Kingdom Hydrographic Office. Designed in consultation with other astronomers of many countries. Provides current, accurate astronomical data for use in the making and reduction of observations and for general purposes. The Astronomical Almanac Online extends the printed version by providing data best presented in machine-readable form. Online data are provided for several years. Contains data for astronomy, space sciences, geodesy, surveying, navigation, and other applications. Also used for navigation by air and water.The Astronomical Almanac is a joint publication of the U.S. Nautical Almanac Office, United States Naval Observatory (USNO), in the United States and Her Majesty's Nautical Almanac Office (HMNAO), United Kingdom Hydrographic Office (UKHO), in the United Kingdom. This annual publication contains precise ephemerides of the Sun, Moon, planets, and satellites, data for eclipses and other astronomical phenomena for a given year, and serves as a world-wide standard for such information.