Question

What is the sun's right ascension on the first day of winter?

Answer 1

The answer is D. 18 hours.

Answer 2

From the point of view of the northern hemisphere:

The sun starts out the year at the Spring equinox, March 21,
Right Ascension 0, Declination 0.

3 months later, Summer solstice, June 21
RA = 6 hours, Dec. = +23.5°

3 months later, Fall equinox, September 21,
RA = 12 hours, Dec. = 0

3 months later, Winter solstice, December 21,
RA = 18 hours,  Dec. = -23.5°