This diagram has been prepared to simplify the method for the identification of stars described in No. 123 of the U. S. NAVAL INSTITUTE and shows the relation

Sin t cos d= sin Z cos h;

from which the declination is found after finding the hour angle from the Azimuth Tables—the azimuth having been observed or found from the Azimuth Diagram.

2. To Find the Star's Declination from the Diagram.

Enter with the azimuth on the margin; the intersection of the horizontal line through this point with the curve corresponding to the true altitude fixes a vertical line, the intersection of which with the horizontal line corresponding to the hour angle previously found, determines the curve corresponding to the declination of the body.

3. Thus in Problem 1, we have Azimuth= N.74°W.; Hour Angle= 72° 24' and Altitude= 29° 30' and we find the Declination= 28° 30'.

Problem 2. Azimuth= S. 110° 25' W.; Altitude= 19° 51' 20"; Hour Angle= 64° 30’; hence we find the Declination= 12°30'.

Problem 3. Azimuth= S. 64° 37' E.; Altitude= 25°55'; Hour Angle= 58° 04'; Declination= 16° 15'.

4. Referring to the Azimuth Diagram published in No. 123, and to paragraph 5 of the paper referred to above:

The Azimuth may be named without reference to its sign by the following precept:

Mark the Azimuth East or West like the Hour Angle. When the Latitude and Declination are of the same name and the Latitude is greater than the Declination and when the Declination is of the contrary name to the Latitude—then the Azimuth is of the contrary name to the Latitude.

When the Latitude and Declination are of the same name and Latitude is less than the Declination and near the Inferior Meridian—then the Azimuth is of the same name as the Latitude.

5. By using formula

Sin Z cos L = sin M cos d (2)

the Position Angle M of a given body may be found, thus:

Enter with the azimuth on the margin; the intersection of the horizontal line through this point with the curve corresponding to the Latitude fixes a vertical line the intersection of which with the curve corresponding to the given declination determines the horizontal line corresponding to the Position Angle of the body.

Supplementary Azimuths, Hour Angles, and Position Angles are given on the right hand margin.

For convenience in use, and in order to preserve the diagram, it should be mounted on heavy cardboard.

{Star Finding Diagram}