The sun is overhead at the tropic of Capricorn on

Analyze the question: The question asks for the date on which the sun is directly overhead (at an angle of 90°) at the Tropic of Capricorn, which lies at latitude 23½°S.

Explain the concept: The Earth's axis is tilted at 23½°, and the Earth revolves around the sun. Because of this, the sun's overhead (vertical) position moves between the Tropic of Cancer (23½°N) and the Tropic of Capricorn (23½°S) during the year.

Key dates:

• March 21 (March equinox): Sun is overhead at the Equator (0°).
• June 21 (June solstice): Sun is overhead at the Tropic of Cancer (23½°N). This is summer in the Northern Hemisphere.
• September 23 (September equinox): Sun is overhead at the Equator (0°).
• December 22 (December solstice): Sun is overhead at the Tropic of Capricorn (23½°S). This is summer in the Southern Hemisphere.

Step-by-step solution:

1. The Tropic of Capricorn is at 23½°S.
2. The sun reaches its southernmost overhead position during the December solstice.
3. Option A (March 21) and option C (September 23) are equinoxes, so the sun is over the Equator.
4. Option D (June 21) is when the sun is over the Tropic of Cancer, in the Northern Hemisphere.
5. Only option B (December 22) matches the Tropic of Capricorn.

Answer: B. December 22

Tip: Remember the pairing: June → Cancer (North), December → Capricorn (South). Both Capricorn and December start with letters that can help you link them: Capricorn and December are the "southern" pair, and the equinoxes (March and September) are always at the Equator. Also, the first letters of "June" and "Cancer" both link to the Northern summer, so you can quickly eliminate the wrong options in the exam.