History of The Air Almanac
Celestial navigation, used for millennia for sailing the seas, became
essential in the 1930s for long aircraft flights, especially over the oceans.
The usual techniques for marine celestial navigation required too much time to
produce a celestial fix while in flight. Driven to produce an almanac designed
to meet the needs of pilots, the various almanac offices around the world
developed new and faster procedures.
In the United States, interest for producing a volume
tailored to the needs of aircraft navigators began in the late 1920s. This interest resulted in the
production of the Aeronautical Supplement for September, 1929 to December, 1930;
the Supplement for 1931; the revised Nautical Almanac for 1932;
The Air Almanac
for 1933; and the revised Nautical Almanac for 1934 and 1936. But despite the
publication of German (1935), French (1936) and British (1937) air almanacs, the
Americans did not produce a regular annual volume during the 1930s.
In 1940, as part of the American efforts in World War II, the Nautical Almanac
Office received permission to increase its staff to produce an air almanac
specially designed for the US air fleet. The office delivered the new Air
Almanac in 1941, and it has been published regularly ever since. This new book
presented the data as a single sheet per day, with much of the data given in 10
minute intervals appropriate for pilots. One sheet per day was a great
convenience for pilots because single pages could be removed and taken on
flights. Each page contained the GHA for Aries, Sun, Moon, and those planets
suitable for navigation for that day, listed in 10 minute intervals for that
day. The new Air Almanac was enthusiastically received. In 1946, George Mixter
wrote in the journal Navigation, (volume 1, number 3):
"The American Air Almanac, a child of necessity is the
best-constructed almanac yet devised for the use of navigators, and marks the
most important step in the simplification of the art of navigation since the
work of Marq-Saint-Hilaire."
Other special items added were the sky diagrams, star finder charts for
periscopic sextants, Moon visibility charts for high latitudes, and a list of
time zones used by various countries.
Initially The Air Almanac was printed in three volumes per year, each
covering a four-month period. Beginning with the 1977 edition, two volumes per
year were printed each with data for six months. This was reduced to one yearly
volume for the 1987 edition. Starting with the 2008 volume, a single CD-ROM replaced
the printed book, and beginning with the 2015 edition, the entire publication was made
available for download from the Internet.
|The edition for 1941 was the first regularly recurring edition produced by the US Nautical Almanac Office. Each year was separated into three volume containing data for four months. It was comb bound, the color of the spine either red, white, or blue depending on the months covered.
|The British and American Air Almanacs were unified. Notation changed from Greenwich Civil Time (GCT) to Greenwich Mean Time (GMT).
| The sky diagrams were extended to include the daylight hours (published as a supplement for 1963 and 1964).
| Precision of the coordinates of the Sun increased to one-tenth of a minute of arc. Reproductions of the unified volume were used by several foreign countries.
| Beginning with the edition for 1969, the daily pages were produced by the Linofilm automatic photocomposing process. Also beginning with this edition, a duplicate set of the daily pages were furnished to France.
| Beginning with the edition for 1970, star recognition diagrams for periscopic sextants were included in lieu of astrograph settings.
| Beginning with the edition for 1973, day of the year was introduced in the headings. The mean hourly rates of the GHA and declination fo the Sun, Moon, and planets were given on the daily pages.
| Beginning with the edition for 1977, two volumes per year were printed each with data for six months. Spines were comb; red for the first six months of the year, blue for the second six months.
| Beginning with the edition for 1987, the Air Almanac was printed annually in one volume. The spine was blue.
| Beginning with the edition for 1999, the comb binding was replaced with perfect binding.
| Beginning with the edition for 2006, a CD-ROM was included that contained all the page images in Portable Document Format (PDF).
| Beginning with the edition for 2008, the paper publication was no longer produced. The Air Almanac became available on CD-ROM, using a web browser interface to navigate through the publication. This made it the first USNO navigational almanac to be available only via digital media.
| Beginning with the edition for 2009, JPL's DE405/LE405 lunar and planetary
ephemerides were used, replacing DE200/LE200.
| Beginning with the edition for 2015, JPL's DE430 lunar and planetary ephemerides
was used, replacing DE405/LE405. Entire almanac was freely available via download at
USNO's and GPO's websites.