Explain the meaning of the terms 'Solstice' and 'Equinox'.

The term 'Solstice' means an event occurring when the Sun appears to reach its most northerly or southerly excursion relative to the celestial equator on the celestial sphere. It occurs on June 21 (Summer Solstice) and December 22 (Winter Solstice).

The time when the Sun crosses the plane of the Earth's Equator making length of the day equal to length of night all over the earth, is known as 'Equinox'. It occurs on March 21 and September 23.