universe & solar system section 5 MCQ Questions & Answers Detailed Explanation

Answer: (d)

As Earth revolves around the Sun, there are two moments each year when the Sun is exactly above the equator. These moments — called equinoxes — occur around March 20 or 21 and September 22 or 23.

Equinox literally means “equal night,” since the length of day and night is nearly equal in all parts of the world during the equinoxes. When the Northern Hemisphere starts to tilt toward the sun in spring, the Southern Hemisphere starts to tilt away from the sun, signalling the start of fall.

Thus, in the Southern Hemisphere, the March equinox is called the autumnal equinox, and the September equinox is called the vernal equinox. The summer solstice occurs when the tilt of a planet’s semi-axis, in either the northern or the southern hemisphere, is most inclined toward the star (sun) that it orbits. Earth’s maximum axial tilt toward the sun is 23° 26’. This happens twice each year, at which times the sun reaches its highest position in the sky as seen from the north or the south pole.

The summer solstice occurs during a hemisphere’s summer. This is the northern solstice in the northern hemisphere and the southern solstice in the southern hemisphere. Depending on the shift of the calendar, the summer solstice occurs sometime between June 20 and June 22 in the northern hemisphere and between December 20 and December 23 each year in the southern hemisphere. Winter solstice is an astronomical phenomenon that marks the shortest day and the longest night of the year.

Winter solstice occurs for the Northern Hemisphere in December and for the Southern Hemisphere in June. The point at which the Sun’s path crosses the celestial equator moving from north to south is called the autumnal equinox. the equinox in autumn, on about 22 September in the northern hemisphere and 20 March in the southern hemisphere.