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assumed longitude

The longitude of the assumed position chosen during a sight reduction to facilitate the use of sight reduction tables. The proper choice depends on your DR-Lon and the minutes part of the sighted body's GHA at the time of the sight. In west longitudes, it is the one longitude that lies within 30' of your DR-Lon that has the same minutes part as that of the GHA.

In east longitudes, it is the one longitude that lies within 30' of DR-Lon that has a minutes part equal to 60' minus the minutes part of GHA. With a-Lon chosen properly, the local hour angle (LHA) of the sighted body will be a whole number of degrees. See Assumed Position.

Abbreviation:  a-Lon

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