Latitude by Meridian Altitude of a Star—Latitude by Polaris
(Pole or North Star)
To find your latitude by taking an altitude of a star when it is on your meridian, is one of the quickest and easiest of calculations in all Navigation. The formula is exactly the same as for latitude by meridian altitude of the sun. In using a star, however, you do not have to consult your Nautical Almanac to get the G.M.T. and from that the declination. All you have to do is to turn to page 95 of the Nautical Almanac, on which is given the declination for every month of the year, of any star you desire. The rest of the computation is, as said before, the same as for latitude by the sun and follows the formula Lat. = Dec. ± Z.D. (90° - true altitude). As when working latitude by the sun, you subtract the Z.D. and Dec. when of opposite name and add them when of the same name. Put in your Note-Book:
Formula: Lat. = Dec. ± Z.D. (90° - true altitude).
At sea, Dec. 24th, 1919. Meridian altitude Star Aldebaran 52° 36' S. HE 20 ft. Required latitude of ship.
| Obs. Alt. | 52° 36' S |
| Corr. | - 5 08 |
| ————— | |
| True Alt. | 52° 30' 52" S |
| - 90 00 00 | |
| ————— | |
| Z.D. | 37° 29' 08" N |
| Dec. | 16 21 00 N |
| ————— | |
| Lat. | 53° 50' 08" N |
Note to Instructor:
Have class work examples such as the following before taking up Latitude by Pole Star:
1. At sea, May 5th, 1919. Meridian altitude Star Capella, 70° 29' S. HE 32 ft. Required latitude of ship.
2. At sea, August 14th, 1919. Meridian altitude Star Vega, 60° 15' 45" N. HE 28 ft. Required latitude of ship.