Sight Reduction Tables

Sight Reduction Tables

Sight Reduction Tables are used in celestial navigation to "reduce" (analyze) the "sights" (data obtained from a sextant at known times) in order to find your latitude and longitude. There are several styles of these tables, but they all do exactly the same thing: You tell the tables a location on earth and a location of a celestial body (the point on earth where the body would be directly overhead), and the tables tell you the angular height of that body above the horizon (viewed from the location you provided) and they tell you the true bearing to the body along the horizon. In the jargon of cel nav, you enter the tables with Assumed Latitude (a-Lat), declination (dec), and Local Hour Angle (LHA) and the tables tell you the calculated altitude (Hc) and azimuth (Zn) of the body. The various styles of tables differ only in how they are laid out and the final precision of the answers.

Detailed instructions on the use of these tables are included in our textbook on Celestial Navigation.

$ (see below)   ...item# 1898

Pub. No. 229 (HO-229)

This is the standard set of tables designed for marine navigation. Although there are 6 volumes in a set, only those volumes covering the latitudes anticipated need be purchased. These are permanent books that do not go out of date. The latitudes listed for the Volumes work for either northern or southern hemisphere.

These as Commercial Editions reproduced from the official Government electronic files. They are economical, and sized at 90% of the originals. They have soft instead of hard covers and their smaller size of 8.5 x 11 inches is easier to carry and store. Weight 2.1 lbs each. $24.95 per volume.

Vol. 1
Lat 0-15
Vol. 2
Lat 15-30
Vol. 3
Lat 30-45
Vol. 4
Lat 45-60
Vol. 5
Lat 60-75
Vol. 6
Lat 75-90

Pub. No. 249 (HO-249)

These tables were originally designed for air navigation, but they have become popular with sailors. Vol 2 and Vol 3 provide conventional sight reduction data, but Vol. 1 offers a faster more direct way to sight reduce stars. Many choose to have Vol 1 for star sight prediction, even if they user other methods for the reduction, because it shows the best 3 stars to use in any setting. Unlike Vol 2 and 3, which are permanent publications, Vol 1 is published every 5 years, labeled by the Epoch year, with the data being valid for the 2 years before and after the Epoch year.

Vol 2 and Vol 3 presented here are commercial reproductions of the official government files. Vol 1 is no longer produced by the US government, but commercial companies have taken on this production on their own. The page sizes are 10% smaller than the government editions, but notably less expensive. They have soft instead of hard covers; they are 8.5" x 11", about 1" thick. Shipping weight is 2.1 lbs. $24.95 per volume.

Vol. 1
Selected Stars, Epoch 2020
Vol. 2
Latitudes 0-40 Declinations 0-29
Vol. 3
Latitudes 39-89 Declinations 0-29


Nautical almanac data for the sun and selected stars valid until 2050, plus easy to use, concise sight reduction and altitude correction tables. Plus work forms to make the process even easier. A concise one-book solution for celestial navigation.

All the information you need for

Finding your position from timed sextant sights
Checking your compass by celestial bearings
Computing great circle routes to your destination

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Item 1882, $29.95


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