# Surveying Questions and Answers – Field Astronomy – Conversion of Time

This set of Surveying Multiple Choice Questions & Answers (MCQs) focuses on “Field Astronomy – Conversion of Time”.

1. Correction for parallax is given as ___________
a) Horizontal parallax * sin of apparent altitude
b) Horizontal parallax * cot of apparent altitude
c) Horizontal parallax * tan of apparent altitude
d) Horizontal parallax * cos of apparent altitude

Explanation: Parallax is a common error which makes a huge effect in obtained output. Correction for parallax is generally applied in all cases which includes the product of horizontal parallax and cos of apparent altitude. It is always an additive value, applied around the horizon.

2. Express the 24˚12ꞌ42ꞌꞌ in hours, minutes and seconds.
a) 4h 36m 50.8s
b) 16h 36m 50.8s
c) 1h 36m 50.8s
d) 1h 6m 20.8s

Explanation: For expressing in hours, minutes and seconds, we have to divide each one with 15. So,
24˚= 24˚/15 = 1h 36m; 12ꞌ = 12ꞌ / 15 = 0h 0m 48s; 42ꞌꞌ = 42ꞌꞌ/15 = 0h 0m 2.8s. On addition, we get
1h 36m 50.8s.

3. Determine the local time if the standard time is 19h 42m 7s and the difference in longitude can be given as 3h 9m towards west.
a) 16h 33m 7s
b) 61h 33m 7s
c) 16h 34m 5s
d) 6h 33m 7s

Explanation: The local time can be determined by using the formula,
Local time = standard time ± difference in longitude. Here, longitude is towards west so we have to use negative direction.
On substitution, we get
Local time = 19h 42m 7s – 3h 9m
Local time = 16h 33m 7s.

4. Find G.M.T of a place if the L.M.T is given as 9h 24m 17s and the longitude 10h 23m 32s towards east.
a) 19h 47m 4s
b) 19h 47m 49s
c) 9h 47m 49s
d) 19h 4m 49s

Explanation: The G.M.T calculation can be done by using the formula,
G.M.T = L.M.T + longitude. On substitution, we get
G.M.T = 9h 24m 17s + 10h 23m 32s
G.M.T = 19h 47m 49s.

5. Which of the following indicate the standard time meridian of India?
a) 82˚3ꞌ
b) 28˚30ꞌ
c) 8˚30ꞌ
d) 82˚30ꞌ

Explanation: The standard time meridian of India can be given as 82˚30ꞌ. The time meridians are taken from Greenwich as a reference. These are adopted for having a different time lines which can have clarity on their respective zones.
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6. The mean time associated with the standard meridian can be given as _________
a) Meridian time
b) Average time
c) Standard time
d) Absolute time

Explanation: Standard time involves mean time association with standard meridian. This difference between standard time and local time at a place is due to longitudinal difference with the standard meridian.

7. The formula of mean solar time can be given as ____________
a) Hour angle + 12h
b) Seconds angle + 12h
c) Minutes angle + 12h
d) Hour angle + 24h

Explanation: Mean solar time can be expressed as the summation of hour angle of the mean sun with 12 hours. This can create the mean solar time which can be used for further scientific calculations.

8. Express the hours (19h 42m 16s) in angles.
a) 259˚34ꞌ
b) 295˚43ꞌ
c) 295˚34ꞌ
d) 25˚34ꞌ

Explanation: For expressing in angles we must multiply each value with 15.
So, 19h = 19*15˚ = 285˚; 42m = 42m*15ꞌ = 10˚30ꞌ; 16s = 16s*15ꞌꞌ = 0˚4ꞌ. On addition, we get
295˚34ꞌ.

9. Which of the following indicates formula for green witch mean time?
a) G.M.T = L.M.T * longitude of the place
b) G.M.T = L.M.T ± longitude of the place
c) G.M.T = L.M.T + longitude of the place
d) G.M.T = L.M.T / longitude of the place

Explanation: The formula for green witch mean time can be given as
G.M.T = L.M.T ± longitude of the place. The sign plus or minus depends upon the direction of the longitude, towards east plus and towards west minus.

10. Calculate mean solar time if the hour angle of the sun is 34h 21m 15s.
a) 46h 21m 15s
b) 64h 21m 15s
c) 46h 12m 15s
d) 46h 21m 51s

Explanation: The mean solar time can be given as
Mean solar time = hour angle of the sun + 12h. On substitution, we get
Mean solar time = 34h 21m 15s + 12h
Mean solar time = 46h 21m 15s.

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