April 22nd, 1919, A.M. at ship. In Lo. 75° E. What is the local mean time of the Star Etamin's meridian passage?
Hence, star will cross meridian at 3h 58m 54s A.M. April 22nd.
2. To find at any hour desired what star will cross your meridian, take the R.A. of the Mean Sun for Greenwich Mean Noon of the proper astronomical day. Apply to it the correction for longitude in time (West +, East -) as per table at bottom of page 2, Nautical Almanac, and the result will be the R.A. of the Mean Sun at local mean noon; i.e., the distance in sidereal time the mean sun is from the First Point of Aries when it is on your meridian. Suppose you wish to find the star at 10 P.M. Add 10 sidereal hours to the sun's R.A. just found. The result will be the R.A. of your meridian at approximately 10 P.M.
Select in the table on p. 94 the R.A. of the star nearest in time to your R.A. just secured. Subtract the R.A. of the Mean Sun at local mean noon from the star's R.A. just found on p. 94 of the N.A. and the result will be the exact distance in sidereal time the star you have just identified is from your meridian, i.e., the time interval from local mean noon expressed in units of sidereal time. Convert this sidereal time interval into a mean time interval by always subtracting for the proper number of hours, minutes and seconds as per Table 8, Bowditch. You will then have secured the name of the star desired and the exact local mean time of the star's meridian passage.
Example No. 2: At sea Dec. 14, 1919. Desired to get a star on my meridian at 11 P.M. Lo. by D.R. 74° W.
| .R.A.G.M.N. | 17h 28m 26s |
| Corr. 74° W. (4th - 56m W + ) | + 0 48.6 |
| ————————— | |
| .R.A. your M. | 17h 29m 14.6s |
| + 11 | |
| ————————— | |
| R.A.M. | 28h 29m 14.6s |
| - 24 | |
| ————————— | |
| 4h 29m 14.6s |
| R.A. of Star Aldebaran | 4h 31m 18.5s |
| Star R.A. | 28h 31m 18.5 |
| .R.A.your M. | 17 29 14.6 |
| ———————— | |
| Sid. Int. from L.M. Noon | 11h 02m 03.9s |
| Red for Sid. Int. (Table 8) | - 1 48 |
| ———————— | |
| L.M.T. | 11h 00m 15.9s |
Aldebaran, then, is the star and the exact L.M.T. of its meridian passage will be 11h 00m 15.9s