Ex27-1 On September 29, 2003 the sun was observed on the rooftop of Geomatics Engineering section of I.I.T. Roorkee having geographical location (Latitude 29° 50' 44'.83 and Longitude 77° 54' 00”.39). The observation was recorded as follows: Temp 14° C and pressure = 969 millibars.
Observation to |
Face |
Time |
Horizontal Angle |
Vernier C and D |
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Vernier A |
Vernier B |
|||||||||||||
Hr |
' |
" |
° |
' |
" |
° |
' |
" |
' |
" |
||||
R.O |
L |
99 |
17 |
40 |
17 |
40
|
||||||||
 |
L |
10 |
04 |
36 |
59 |
05 |
40 |
05
|
20
|
22
|
37 |
00 |
37 |
20 |
 |
L |
10 |
05 |
58 |
58 |
50 |
40 |
50
|
40
|
22
|
33 |
20 |
33 |
20 |
 |
R |
10 |
07 |
49 |
238 |
10 |
20 |
10
|
20
|
22
|
30 |
20 |
30 |
40 |
 |
R |
10 |
08 |
32 |
237 |
10 |
40 |
10
|
20
|
22
|
25 |
20 |
25 |
40 |
R.O |
R |
279 |
18 |
20 |
18 |
20 |
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Find out the azimuth of the line joining the station and reference object.
Figure Example 27.1
Solution : Refer figure 26.3
The latitude (f) of the station = 29° 51' 44”. 83
The longitude (l) of the station =77° 54' 00”. 39
The date of observation September 29, 2003.
To determine the azimuth of the line joining the observation station and the reference object, say AZ.
Let as consider observation with face left condition of the instrument.
The time of observation, UTI = 10h 04m 36s
Then, GHA = UTI+ R (Exess)
From star almanac, R on September 29 (2003) at 10h 04m 36s
= 0h 30m 21.7s + 41.3s = 0h 31m 3.01s
GHA = 0h 31m 3.01s + 10h 04m 3.01s
=10h 35m 39.01s
Thus, LHA = GHA + l
= 10h 35m 39.01s +77° 54' 00”.39 = 236° 48' 45".54
From star almanac, apparent declination of the sum, d (at the instant of observation) = S 2° 15' 30" + 3' 54" = S 2° 19' 24"
Now, from equation 26.3
Since the sun was observed in the afternoon, it was observed in western hemisphere.
Thus, azimuth of the sun = 360° - 74° 09' 54”.34
= 285° 50' 05”.65
From, the observation of vertical angle, the apparent altitude (a' )of the sun = 22° 37' 10”
Parallax corection = + 8.8" cos a'
= + 8.8" cos 22° 37' 10" = + 8".123
Semi diameter = +
= + 16'.0 (from star almanac)
The mean refraction error (ro) = 139"
As temperature and pressure during observation are 14° C and 969 millibar, the factor for refraction correction, f = 0.95 (From star almanac).
= 22° 51' 06".123Thus refraction correction = - 139" x 0.95
= - 132".05 = -2' 12"
Therefore, The altitude of the sun
= 22° 37' 10" + 0° 16'.0 + 0° 0' 8".123 - 0° 2' 12"
Thus, horizontal angle of the sun = observed horizontal angle of the sun - Semi diameter correction
= 59° 05' 40" -
= 59° 05' 40" - 17' 21".4589 = 58° 48' 18".54
Therefore, The horizontal angle between the sun and the R.O.
HA = 99° 17' 40" - 58° 48' 10".54 = 40° 29' 29".46 (Left)
The azimuth of the line joining the station and the reference object = Azimuth of the sun + HA
= 285° 50' 05".65 + 40° 29' 29".46 = 326° 19' 35".11