This page allows you to obtain all the astronomical information necessary to plot navigational lines of position from observations of the altitudes of celestial bodies. Simply fill in the form below and click on the "Get data" button at the end of the form.
A table of data will be provided giving both almanac data and altitude corrections for each celestial body that is above the horizon at the place and time that you specify. Sea-level observations are assumed. The almanac data consist of Greenwich hour angle (GHA), declination (Dec), computed altitude (Hc), and computed azimuth (Zn). The altitude corrections consist of atmospheric refraction (Refr), semidiameter (SD), parallax in altitude (PA), and the sum Refr + SD + PA. The SD and PA values are, of course, non-zero only for solar system objects.
Note: For the original USNO forms, please click here.
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This web page was last updated 06/08/22