Question

Where are the days and nights of equal length all year long?
A. At the equator
B. At $$66.5{}^o$$
C. At $$23.5{}^o$$
D. Nowhere

Answer 1

Hint: An equinox occurs as the plane of the Earth's equator intersects the angular centre of the Sun's disc. This happens twice a year, on the 20th of March and the 23rd of September. In other words, it is the time that the apparent Sun's core is immediately above the equator.

Complete answer:
The northern hemisphere's winter and the southern hemisphere's summer are now drawing to a close. That means the days and nights are getting closer to being the same duration, and the Sun's direction through the sky is shifting. The Sun is low in the sky on a winter day, while the Sun is even higher on a summer day.

The Sun would be apparent directly above the equator on a given day in the spring or autumn, right in the centre of the two arcs traced by the Sun in the summer and winter.Winter in the northern hemisphere and summer in the southern hemisphere are now coming to an end. That means the days and nights are getting closer to being equal in duration, and the Sun's path through the sky is changing.

On a winter day, the Sun is low in the sky, while on a summer day, the Sun is much higher. For a given day in the spring or fall, the Sun will be directly over the equator, right in the middle of the two arcs traced by the Sun in the summer and winter.

Hence, option (A) is correct.

Note: The vernal equinox (around March 21) is when the day and night are of equal duration, signalling the beginning of spring. Summer solstice (June 20 or 21): the year's longest day, signalling the beginning of summer. Autumnal equinox (around September 23): day and night are of similar duration, signalling the beginning of the fall season.