Astronomy Principles and Practice Fourth Edition.pdf

h m s Date
Approximate ZT 16 30 0 June 1st
Zone +7
Approximate GD 23 30 0 June 1st, using equation (9.15)
Chronometer time 23 31 20
Error (slow) +1 10
Correct GD 23 32 30 June 1st
Hence, GHAMS is 11 32 30 using equation (9.13)
+2 19
GHA⊙ 11 34 49 using (A)
Longitude (W) −6 54 40
HA⊙ 4 40 9 using equation (9.2).
In the second last line, the longitude has been converted, thus
103 ◦ 40 ′ = 6 × 15 ◦ + 13 ◦ + 40 ′ = 6 h + 52 m + 160 s = 6 h 54 m 40 s .
Twilight 109
Example 9.7. Find the LST and the hour angle of the star Regulus (RA 10 h 5 m 11 s ) from the following
data: Zone, +4; approximate zone time, 3 h 14 m January 4th; chronometer reads 7 h 12 m 56 s at the time
of observation; chronometer error, 2 m 5 s slow on GMT; longitude of observer, 58 ◦ 20 ′ WatUT0 h ,
January 4th, the value of the GAST is 6 h 53 m 34 s .
We proceed in the usual way:
h m s Date
Approximate ZT 3 14 0 January 4th
Zone +4
Approximate GD 7 14 0 January 4th
Chronometer time 7 12 56
Error (slow) +2 5
Correct GD +7 15 1 January 4th
The interval of mean solar time to be converted into sidereal time is, therefore, 7 h 15 m 01 s − 0 h =
7 h 15 m 01 s .
Then,
7 h 15 m 01 s = 7 h 15·m01667 = 7·h250 28 MST.
Hence,
7·h250 28 MST = 7·h250 28 × 366 1 4 /365 1 4 ST = 7·h270 13 ST.
Converting to hours, minutes and seconds, we get
to the nearest second.
7·h270 13 = 7 h 16·m2078 = 7 h 16 m 12·s47 or 7 h 16 m 12 s
h m s
The GAST at UT 0 h , January 4th is 6 53 34
Add the sidereal time interval of 7 16 12
Hence, the GAST at observation time is 14 09 46
Longitude (W) is, after conversion, 3 53 20
Therefore, the LST is 10 16 26 using equation (9.2)
But the RA of the star is 10 05 11
Hence, the HA of the star is 0 11 15 using equation (9.1)
The longitude 58 ◦ 20 ′ was converted in the usual way to 3 h 53 m 20 s .