250+ TOP MCQs on Field Astronomy – Conversion of Time and Answers

Surveying Multiple Choice Questions 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
Answer: d
Clarification: 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) 4^h 36^m 50.8^s
b) 16^h 36^m 50.8^s
c) 1^h 36^m 50.8^s
d) 1^h 6^m 20.8^s
Answer: c
Clarification: For expressing in hours, minutes and seconds, we have to divide each one with 15. So,
24˚= 24˚/15 = 1^h 36^m; 12ꞌ = 12ꞌ / 15 = 0^h 0^m 48^s; 42ꞌꞌ = 42ꞌꞌ/15 = 0^h 0^m 2.8^s. On addition, we get
1^h 36^m 50.8^s.

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

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

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

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
Answer: b
Clarification: 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 + 12^h
b) Seconds angle + 12^h
c) Minutes angle + 12^h
d) Hour angle + 24^h
Answer: a
Clarification: 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 (19^h 42^m 16^s) in angles.
a) 259˚34ꞌ
b) 295˚43ꞌ
c) 295˚34ꞌ
d) 25˚34ꞌ
Answer: c
Clarification: For expressing in angles we must multiply each value with 15.
So, 19^h = 19*15˚ = 285˚; 42^m = 42^m*15ꞌ = 10˚30ꞌ; 16^s = 16^s*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
Answer: b
Clarification: 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 34^h 21^m 15^s.
a) 46^h 21^m 15^s
b) 64^h 21^m 15^s
c) 46^h 12^m 15^s
d) 46^h 21^m 51^s
Answer: a
Clarification: The mean solar time can be given as
Mean solar time = hour angle of the sun + 12^h. On substitution, we get
Mean solar time = 34^h 21^m 15^s + 12^h
Mean solar time = 46^h 21^m 15^s.