Problem 4th

[p. 13:] From the latitude of place observation together with the time at place observation and the estimated Greenwich time, to compute the altitude of sun, moon, or any known star.

Directions

1. Find the declination of the body for the estimated Greenwich time.
2. Find the hour angle of the body at the given time. The altitude may then be computed by Form 4th as in the following examples.

Example 1st

Suppose the latitude 40°N, Greenwich time May 7th 1799 about 17 hours p.m. Time at place observation 3h 42m p.m. Required the true and apparent altitude of sun's centre.

[p. 14:]

Form IV (A)

[p. 15:]

Example 2nd

Suppose the latitude 22°40' N, Greenwich time June 16th 1799 about 15 hours p.m. Time at place observation 11h 32m p.m. Required the true and apparent altitude of the moon's centre.

Form IV (B)

Example 3d

[p. 16:] Suppose the latitude 45°10' N, Greenwich time January 31, 1799 about 18 hours p.m. Time at place observation 12h 40m p.m. Required the true and apparent altitude of the star Aldebaran?

[p. 17:] Note   When the declination = 0; then to the cosine of the latitude add the cosine of the hour angle and the sum (abating 10 from the index) will be the sine of the true altitude.--

And when the latitude = 0; then to the cosine of the declination add the cosine of the hour angle and the sum (abating 10 from the index) will be the sine of the true altitude.

When both latitude and declination = 0; then the complement of the hour angle will be the true altitude.

Examples for practice

--Edited by Robert N. Bergantino, 05/05, 09/04, 06/05

Funded in part by a grant from the NPS Challenge-Cost Share Program.