Plain English Meaning
A reference book of star, Sun, Moon, and planet positions for every day and time of the year. A navigator uses these tables, along with sightings of those bodies, to figure out where the aircraft is.
Full Definition
A publication, issued jointly by the U.S. Naval Observatory and Her Majesty's Nautical Almanac Office, that provides tabulated astronomical data — including the Greenwich Hour Angle and declination of the Sun, Moon, planets, and selected stars — at regular time intervals throughout the year. It is used in celestial navigation to determine an aircraft's position from observations of celestial bodies.
Context Anchor
Seen in night operations and regulations when determining whether a flight is being made during day, night, or civil twilight.
Derivation
‘Almanac’ comes from Medieval Latin ‘almanachus,’ meaning a calendar or table of astronomical events. ‘Air’ distinguishes this version from the older Nautical Almanac used at sea — the Air Almanac is formatted for the faster pace of flight, with data tabulated at shorter time intervals so an airborne navigator can find values quickly.
Why Pilots Care
Provides a reliable backup method for determining position and heading when electronic navigation systems are unavailable or unreliable.
Intuition Check
Do not read “Air Almanac” as a general flying handbook. Here it means a specific yearly reference for official sky and daylight data used in aviation.
Example Sentence 1
Before the long over-water leg, the navigator pulled out the Air Almanac to look up the Sun's position for the planned time of the next sextant shot.
Example Sentence 2
During the overwater ferry flight, the crew used data from the Air Almanac to verify their position with star observations.