Question

The length of the day from today when the sun is directly overhead till tomorrow again when the sun is directly overhead can be determined by the

• A. rotation of earth about its own axis.
• B. revolution of earth around sun.
• C. inclination of axis of rotation of earth from the plane of revolution.
• D. rotation of earth about its own axis as well as its revolution around sun.

Answer 1

Answer: (D)

rotation of earth about its own axis as well as its revolution around sun.

It depends on both revolution and rotation of earth about its own axis and sun respectively. First, Earth's orbit is an ellipse, not a circle, so the Earth moves faster when it is nearest the Sun (perihelion) and slower when it is farthest from the Sun (aphelion) (kepler's laws of planetary motion). Second, due to Earth's axial tilt, the Sun's annual motion is along a great circle (the ecliptic) that is tilted to Earth's celestial equator. Thus, it depends upon both Earth's rotation about its own axis and revolution around Sun.