To find the Latitude and Longitude of a given Star.

1. Bring the pole of the ecliptic, which is in the same hemisphere with the given star, to the brass meridian, and fix over it the quadrant of altitude.

2. Holding the globe steadily, move the quadrant till it come over the given star; then the degree of the quadrant cut by the star is its latitude, and the degree on the ecliptic cut by the quadrant is its longitude.

That part of the heavens north of the ecliptic is called the northera hemisphere, and that south of the ecliptic the southern hemisphere; so that a star may be north of the equinoctial, and yet have S. latitude,— or south of the equinoctial, and have N. latitude.

The longitude of celestial bodies is not reckoned in degrees and mi

nutes, as the right ascension is, but in signs, degrees, and minutes, in the same manner as the sun's place, which is only another name for the sun's longitude.

The quadrant of altitude is fixed upon the pole of the ecliptic, because in that position, it will be perpendicular to every point of the ecliptic, and therefore represent circles of longitude.

EXAMPLES.

Required the lat. and long. of the following stars:

The day of the month being given, to find at what hour any Star comes to the Meridian.

BY THE GLOBE.-1. Bring the sun's place to the meridian, and set the index to 12 o'clock.

2. Turn the globe round till the given star come to the meridian, and the index will show the hour.

If the star be to the E. of the sun, it will come to the meridian after the sun, and hence the hour will be p.m.; but if the star be to the W. of the sun, the hour will be a.m.

WITHOUT THE GLOBE.-Find the sun's right ascension for the day, by the table in White's Ephemeris, or by Table II. at the end of this work; and find the rt. as. of the star from Table III. or from any catalogue of stars.

Subtract the sun's right ascension from that of the star, (both being expressed in time,) and the remainder will be the time of the star's coming to the meridian.

If the right ascension of the sun be greater than that of the star, add to it 24 before you subtract; and the remainder, if less than 12, is the time of the star's coming to the meridian in the afternoon; if the remainder be greater than 12, take 12 away, and the last remainder is the time of the star's coming to the meridian in the morning.

EXAMPLES.-At what hour do the following stars come to the meridian on Feb. 9th ?

1. Lyra?

2. Aldebaran ?

3. Arcturus?

4. Capella?

5. Sirius?

6. Regulus?

Ans. 9 h. 1 m. a.m.

Ans. 6 55

7. Castor?

8. Fomalhaut?

9. Markab?

10. Atair?

p.m.

The first example performed without the globe.

The sun's right ascension, on Feb. 9th, is 21 hrs. 29 min.; the right ascension of Lyra is 18 hrs. 30 min. ; to the last add 24, and from the sum 42 hrs. 30 min., subtract 21 hrs. 29 min.: the remainder is 21 hrs. 1 min. From this remainder take away 12, and there are left 9 hrs. 1 min. ; which is the time of the star's coming to the meridian in the morning.

Required the time at which the following stars come to the meridian on the respective days.

At what hour does Alphard (Hydra's Heart) on

PROBLEM V.

To find on what Day of the Year any Star passes the Meridian at any given hour.

BY THE GLOBE.-1. Bring the given star to the meridian, and set the index to the given hour.

2. Turn the globe till the index point to 12 at noon; the day of the month, corresponding to the degree of the ecliptic under the meridian, will be the day required.

WITHOUT THE GLOBE.-1. If the star come to the meridian in the morning, add the time that it wants to noon to the right ascension of the star, and the sum will be the right ascension of the sun on the required day.

2. If the star come to the meridian in the evening, subtract the time from noon from the star's right ascension, and the remainder will be the sun's right ascension.

3. The day of the month, answering to this right ascension, may be found from Table II.

If, in adding, the sum is more than 24h., or 360°, subtract from it 24h., or 360°, and the remainder will be the sun's right ascension.

If, when you subtract, the r. as. of the star is less than the time from noon, add to it 24h., or 360°, before subtracting.

EXAMPLES.-1. On what day does Algenib, in Perseus, come to the meridian at midnight?

Here 3h. 10m., the right ascension of Algenib, added to 12h., the time from noon, gives 15h. 10m., the sun's right ascension; the day in the Table answering this R. A. is Nov. 12.

2. On what day does Spica Virginis come to the meridian at half-past nine in the evening? Ans. May 18th. On what days do the following stars come to the meridian at midnight?

3. Algol?

4. Betelguese?

5. Acubens, Cancer?
6. Alioth, Great Bear, &?

E

On what days do the following stars come to the meridian at nine o'clock in the evening?

7. Ras Alhague?

8. Rastaben?

9. Leo, B?

10. Pegasus, B?

Required the days on which the following stars come to the meridian, at five o'clock in the morning.

On what days do the following stars come to the meri

dian at ten o'clock in the evening?

17. Orion, E. 18. Acubens.

19. Alderamin.

On what days does Acturus come to the meridian, at

The Latitude, Hour of the Night, and Day of the Month, being given, to find the Altitude and Azimuth of any Star.

Elevate the globe for the given latitude, bring the sun's place to the meridian, and set the index to 12; and turn the globe till the index point to the given hour.

Fix the quadrant of altitude on the zenith, and bring it over the star; then the degree upon the quadrant cut by the star will be its altitude, and the distance between the foot of the quadrant and the north or south point of the horizon will be the azimuth.

EXAMPLES.-1. Required the altitude and azimuth of Cor Leonis, at London, on May 11th, at 11 o'clock p.m. Ans. Alt. 26° 50′. Az. S. 76° 30′ W. 2. Required the altitude and azimuth of Capella, at Rome, on December 2nd, at five in the morning.

Ans. Alt. 42°. Az. N. 60° W.

What are the altitude and azimuth of the following stars, at Newcastle, October 6th, at the following hours?