2. October 26th, 1919. In latitude 39° 54' S. Observed altitude Star Rigel, West of meridian 42° 18' 40". CT 27d 10h 32m 55s A.M. CC 2m 18s fast. IE 4' 20" off arc. HE 42 ft. Required longitude in.
3. April 11th, 1919. P.M. at ship. In latitude 43° 16' 48" S. Observed altitude Star Spica 33° 18' 20", East of meridian. CT 11h 08m 44s P.M. IE 3' 20" on arc. CC 4m 18s slow. HE 39 ft. Required longitude in.
4. September 15th, 1919. P.M. at ship. In latitude 49° 38'N. Observed altitude Star Deneb, East of meridian, 36° 16' 50". IE 3' 40" off arc. HE 40 ft. CC 6m 18s slow. CT 10h 00m 13s P.M. Declination of star is 44° 59' 36" N. Required longitude in.
If any time is left, work same examples by Marc St. Hilaire Method assuming a position near the one found by Time Sight.
Assign for Night Work any of the above examples, to be worked either as Time Sights or by the Marc St. Hilaire Method, and also the following Arts. in Bowditch: 326-327-328-329.
THURSDAY LECTURE
Latitude by ex-meridian Altitude of the Sun
You have learned that when you calculate your latitude from a meridian altitude of the sun, one of the necessary requisites is to have the sun exactly on your meridian. In fact, that is just another way of expressing meridian altitude, i.e., an altitude taken when the sun is on your meridian. Now suppose that 10 or 15 minutes before noon you fear that the sun will be clouded over at noon so that a meridian altitude cannot be secured. There is a way to calculate your latitude, even though the altitude you secure is taken by sextant some minutes before or after noon. This is called latitude by an ex-meridian altitude. It must be kept in mind that this method can be used accurately only within 26 minutes of noon, either before or after, and only then when you know your longitude accurately. Put in your Note-Book:
1. Get your L.A.T. (S.H.A.).