Question

In northern hemisphere, 21st March is called as
A. Vernal equinox
B. Autumnal equinox
C. Both A and B
D. None of the above

Answer 1

Hint:
1. It has two moments in the year when the Sun is exactly above the Equator and day and night are of equal length.
2. It is one of the two points in the sky where the elliptic and the celestial equator converge (the annual pathway of the Sun).

Complete answer:
Option A. Vernal equinox: The vernal equinox occurs in the Northern Hemisphere around March 20 or 21, when the Sun reaches the northbound celestial equator. The vernal equinox also marks the beginning of spring, which lasts up to the summer solstice, according to the astronomical concept of seasons. Hence, this option is correct.

Option B. Autumnal equinox: The autumnal equinox occurs in the Northern Hemisphere around September 22 or 23, when the Sun reaches the celestial equator, heading south. The autumnal equinox also signifies the beginning of autumn, which lasts until the winter solstice, according to the astronomical concept of seasons. Hence, this option is incorrect.

Option C. Both A and B: The Vernal equinox is the first day of the spring season, which occurs as the sun reaches the equator, moving from the south to the northern hemisphere and the North Pole begins to lean toward the sun again. Vernal equinox is near 20 March. And the Autumnal equinox is the first day of the autumn season and occurs when the sun passes the equator moving from the northern to the southern hemisphere. Autumn equinox is near 22 September. Hence, this option is incorrect.

Option D. None of the above: The March equinox marks when the Northern Hemisphere starts to tilt toward the sun, which means longer, sunnier days. In the Northern Hemisphere, the March equinox is called the vernal equinox, because it signals the beginning of spring (vernal means fresh or new like the spring). Hence, this option is incorrect.

Hence the correct answer is option ‘D’.

Note:
1. An equinox is generally known as the moment of time when the plane of the Earth's equator (extended forever in all directions) moves through the geometric core of the disk of the Sun.
2. Hemisphere-neutral names are the northward equinox for the March equinox, suggesting that the solar declination is crossing the northward direction of the celestial equator at that moment, and the southward equinox for the September equinox, indicating that the solar declination is crossing the southward direction of the celestial equator at that moment.