Official publication prepared jointly with Her Majesty's Nautical Almanac Office of the United Kingdom Hydrographic Office and the United States Naval Observatory's Nautical Almanac Office. Designed in consultation with other astronomers of many countries, it 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. Also used for navigation by air and water.  This resource aids in determining and distributing the timing and astronomical data required for accurate navigation and fundamental astronomy.   The Air Almanac, Astronomical Phenomena, and The Astronomical Almanac Online provide astronomical data, mainly in tabular form, for use in navigation, surveying, scientific research, litigation, accident reconstruction, and many other activities. Issued annually, the almanacs contain data for one year. These publications are prepared jointly with Her Majesty's Nautical Almanac Office, United Kingdom Hydrographic Office.  Each edition contains data for one year and is published six months or more in advance of the edition year.