# Solar Energy Questions and Answers – Solar Time (Locał Apparent Time)

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This set of Solar Energy Multiple Choice Questions & Answers (MCQs) focuses on “Solar Time (Locał Apparent Time)”.

1. What is solar time?
a) Calculation of passage of time based on sun’s position in sky
b) Calculation of passage of time based on moon’s position in sky
c) A unit that measures astronomical time
d) A reference unit for time

Explanation: Solar time is the calculation of passage of time based on sun’s position in sky. It is not calculated based on moon’s position. In astronomy, if required, time is measured in terms of speed of light.

2. What is the fundamental unit of solar time?
a) Seconds
b) Day
c) Hour
d) Meter

Explanation: The fundamental unit of time is day. Meter is not a measurement of time. It is a unit and measurement of distance.

3. What are the two types of solar time?
a) Fundamental solar and multi-solar time
b) Apparent and diurnal solar time
c) Apparent solar time and mean solar time
d) Mean solar time and single-solar time

Explanation: The two types of solar time are apparent solar time and mean solar time. Fundamental solar time, multi-solar time and single-solar time do not exist.

4. What is apparent time also known as?
a) Clock time
b) Revolution time
c) Lunar time
d) Sundial time

Explanation: Apparent time is also known as sundial time. Lunar time is basically the length of one day on moon with respect to earth. Revolution time depends on the speed of revolving body and the distance between body around which it revolves and itself.

5. Which of the following is the simplest sundial?
a) A tall pole casting a shadow whose length and position varies with sun’s position
b) A tall pole
c) A tall pole casting a shadow that varies with moon’s position
d) A stone slab

Explanation: Among the above options, a tall pole casting a shadow is the simplest sundial. It should be noted that both, the length and position of the shadow must vary with sun’s position. A tall pole casting a shadow that varies with moon’s position is not a sundial.

6. What is mean solar time also known as?
a) Rotation time
b) Clock time
c) Lunar time
d) Sundial time

Explanation: Mean solar time is also known as clock time. Apparent solar time is also known as sundial time. Lunar time is the length of a day on moon as compared to earth. Rotation time is the time a body takes to rotate about an axis.

7. Solar time is _____ clock time in December and ____ clock time in September.
a) same as, same as
b) less, more
c) more, less
d) more, same as

Explanation: Solar time is more than clock time in December. However, it is less than clock time in September. It is almost same as the clock time during the other months.

8. Why is does the solar time vary in September and December?
a) Because of earth-moon distance
b) Because of earth-moon gravitational force
c) Because of eccentricity of sun-moon orbit
d) Because of eccentricity of earth-sun orbit

Explanation: Solar time varies because of the eccentricity of earth-sun orbit. Earth’s orbit around the sun is elliptical and not perfectly circular. The variation in solar time does not depend on sun-moon and earth-moon distance/orbit.

9. The clock running at a constant (say, a pendulum clock) rate _____
b) always follows the sun
c) follows the sun randomly
d) follows the moon

Explanation: The clock running at a constant (say, a pendulum clock) rate cannot follow the sun. This is because of the elliptical nature of earth’s orbit and the tilt of earth’s axis.

10. What does a clock running at a constant rate follow?
a) Moon
b) Imaginary mean sun
c) Actual sun
d) Real mean sun

Explanation: A clock running at constant rate does not and cannot follow the actual sun. Instead, it follows an imaginary mean sun. This imaginary sun moves at a constant rate along a celestial equator. The motion is such that it matches the real sun’s average clock over the period of a year.

11. What is apparent solar day?
a) Interval between sunrise and sunset of a normal day
b) Interval between two successive returns of sun on equator
c) Interval between two successive returns of sun on local meridian
d) Imaginary solar day

Explanation: The interval between two successive returns of sun on local meridian is called apparent solar day. The apparent motion of the actual sun is governs apparent solar time.

12. Which of the following describes the elliptical nature of earth’s orbit?
a) Apparent solar time
b) Sundial
c) Maxwell’s laws
d) Kepler’s laws

Explanation: Kepler’s laws describe the elliptical nature of earth’s orbit. Maxwell’s laws are related to electrodynamics. Sundial is an instrument used to measure apparent solar time.

13. The hour angle of the mean sun plus 12 hours is _______
a) mean solar time
b) angled solar time
c) offset solar time
d) apparent solar time

Explanation: The hour angle of the mean sun plus 12 hours is called the mean solar time. The 12 hour offset is used to ensure that each day starts at midnight for civil purposes. The hour angle or mean sun is measured from local meridian.

14. Solar time is 21 seconds less than clock time in September and 29 seconds more than clock time in December.
a) True
b) False

Explanation: Solar time is 21 seconds less than clock time in September and 29 seconds more than clock time in December. This is due to the eccentricity of earth’s orbit around the sun i.e. it is not perfectly circular.

15. The inclination of earth’s axis also contributes towards variation in solar time.
a) True
b) False 