The Air Almanac contains the astronomical data required for air celestial navigation. The download-version contains the same data found on the CD-ROM, but in a single bookmarked PDF.  It provides the following data tabulated at 10-minute intervals to a precision of 1 arcminute: the Greenwich hour angle and declination of the Sun, Moon, and three navigational planets; the Greenwich hour angle of Aries; rise and set times of the Moon for a range of latitudes; and other data. Each edition also contains sky diagrams for each month; sunrise, sunset, and twilight tables; and positions of the navigational stars.  The data are produced in collaboration between The U.S. Naval Observatory in the U.S. and Her Majesty's Nautical Almanac Office (HMNAO) in the UK. HMNAO maintains the copyright on the material it produces.