2. Take from the Nautical Almanac, and correct for the Greenwich date, the following quantities: star's declination and star's right ascension, right ascension of mean sun, moon's right ascension and moon's declination; moon's semidiameter and moon's horizontal parallax.

3. To find star's hour angle.

To the right ascension of mean sun add mean time at ship,* and from the sum subtract the star's right ascension; the remainder is the hour angle of the star.

* Ship mean time is found by an altitude of a heavenly body taken a little before or after the lunar as directed, p. 229.

4. To find the moon's hour angle.

From the same sum (viz. right ascension of mean sun and ship mean time) subtract the moon's right ascension ; the remainder is the hour angle of the moon.

5. To calculate the star's true altitude.

Proceed as in 4, p. 230, using the star's declination instead of the sun's.

To find star's apparent altitude.

To the true altitude just found add the refraction; the result is the star's apparent altitude.

6. To find the moon's true and apparent altitude proceed as in 6, p. 231.

7. Proceed then as in former rule (arts. 6, 8, 9, p. 211).

EXAMPLE.

May 16, 1842, in lat. 50° 37′30′′ N., and long. by account 1° 6' W., when a chronometer showed 10h 39m 26s P.M., the observed distance of the star a Virginis from the moon's farthest limb was 64° 1′ 50′′, index correction + 0' 40", the error of the chronometer on ship mean time being fast 4m 14s; required the longitude.

To calculate star's altitude. To calculate moon's altitude.

Hav. star's hour angle. 8-158830 Hav. moon's hour ang.

6.301030

9.802359

9.988095

9.549884

(215) April 20, 1847, in lat. 50° 37′ 12′′ N., and long. by account 1° 6′ W., when a chronometer showed 8h 58m 45s P.M., the observed distance of the star a Leonis from the moon's farthest limb was 46° 2′ 12", index correction +0' 30", the error of chronometer being fast 3m 22s; required the longitude. Ans., 0° 55′ 45′′ W.

(216.) December 10, 1845, in lat. 50° 37′ 30′′ N., and long. by account 1° 6′ W., when a chronometer showed 9h 24m 488.3 P.M., the observed distance of the star Pollux from the moon's farthest limb was 65° 28′ 30′′, index correction + 0' 30", the error of the chronometer on ship mean time being fast 12m 50s-8; required the longitude.

Ans., 0° 44′ 15′′ W.

(217) April 19, 1847, in lat. 50° 48′ N., and long. by

account 1° 6′ W., when a chronometer showed 8h 40m 18s P.M., the observed distance of the star Regulus from the moon's farthest limb was 59° 11′ 1′′6, index correction +30", the error of the chronometer on ship mean time being fast 9m 30°-4; required the longitude.

Ans., 1° 7' W.

(218.) September 1, 1843, in lat. 50° 37′ 30′′ N. and long. by account, 1° 6' W., when a chronometer showed 8h 2m 54s.4 P.M., the observed distance of the planet Jupiter from the moon's farthest limb was 64° 19′ 57′′, index correction +1′50′′ the error of the chronometer on ship mean time being fast 2m 256; required the longitude.

Ans., 0° 35′ 15′′ W.

(219.) September 5, 1843, in lat. 50' 48" N., and long. by account 1° 6' W., when a chronometer showed 8° 52′ 39′′ P.M., the observed distance of the planet Mars from the moon's nearest limb was 45° 11′ 23′′-3, index correction +1'50", the error of the chronometer being fast 4m 478.4; required the longitude. Ans., 1° 19′ 45′′ W.

17° 36 40 N.

Mean sun's right asc. 1h 51m 48-09

Moon's semi.
Noon. 15′ 23′′7

Hor. par. 56′ 29′′S

Mid. 15 17 0

.

April 20

Moon's right ascen. 20th, at 8h. 6h 51m 38-8

10th

9h

6 53 16.8
Distance at 6 hours, 46° 51′ 27′′; at 9 hours, 45° 16′ 23′′.

Star's declin.

28° 23′ 22′′ N.

Mean sun's right asc. 17h 16m 17-09

Star's right ascen. 7h 35m 54.9

9h. 5 58 59.68
Mid. 15' 30 9
Distance at 6 hours, 59° 46′ 25′′; at 9 hours, 58° 8′ 6′′.

Hor. par.

57' 23 5

.

56 56.1