Q.7 Define briefly the following terms and mention the dates on which these are experienced :-
(a) Solstice (b) Equinox (c) Aphelion (d) Perihelion.
Answers
Answer:
(a) A solstice is an event occurring when the Sun appears to reach its most northerly or southerly excursion relative to the celestial equator on the celestial sphere. Two solstices occur annually, around June 21 and December 21. The seasons of the year are determined by reference to both the solstices and the equinoxes.
(b) An equinox is commonly regarded as the instant of time when the plane (extended indefinitely in all directions) of Earth's equator passes through the center of the Sun. This occurs twice each year: around 20 March and 23 September. In other words, it is the moment at which the center of the visible Sun is directly above the Equator.
(c) The aphelion is the point in the orbit of an object where it is farthest from the Sun. The point in orbit where an object is nearest to the sun is called the perihelion. The Earth's orbit has its aphelion about July 4.
(d) The perihelion is the point in the orbit of a planet, asteroid or comet that is nearest to the sun. It is the opposite of aphelion, which is the point farthest from the sun. Perihelion always occurs near January 4th, while aphelion lands near the 4th of July.
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