An equinox occurs twice a year when the Sun is vertically overhead which line of latitude on the Earth, resulting in nearly equal day and night duration all over the world?

Introduction / Context:
The apparent movement of the Sun across the sky throughout the year is due to the tilt of the Earth's axis and its revolution around the Sun. This leads to important dates such as solstices and equinoxes, which mark changes in seasons. An equinox is a special time when day and night are nearly equal everywhere on Earth. Knowing where the Sun is overhead at this time is a common topic in geography and astronomy related general knowledge questions.

Given Data / Assumptions:
- The question refers to equinox, which occurs twice a year (around March 21 and September 23).
- It mentions the Sun being vertically above a specific line of latitude.
- Options include the Tropic of Capricorn, Tropic of Cancer, the poles, and the Equator.
- We assume standard definitions of solstices and equinoxes used in school geography.

Concept / Approach:
On an equinox, the Sun is directly overhead at noon at the Equator (0° latitude). This happens approximately on March 21 (vernal equinox) and September 23 (autumnal equinox). Around these dates, every place on Earth experiences nearly 12 hours of daylight and 12 hours of darkness. By contrast, during solstices the Sun is overhead at one of the tropics: the Tropic of Cancer in June and the Tropic of Capricorn in December. The poles are never overhead positions for the Sun. Therefore, the equinox is associated with the Equator, not with the tropics or the poles.

Step-by-Step Solution:
Step 1: Recall that equinox means “equal night,” referring to nearly equal day and night durations. Step 2: Remember that on equinox dates, the Sun's vertical noon rays fall on the Equator. Step 3: Distinguish this from solstice dates, when the Sun is overhead at the Tropic of Cancer (June) or Tropic of Capricorn (December). Step 4: Note that the poles are not overhead positions for the Sun because of the Earth's tilt. Step 5: Choose the Equator as the correct line of latitude for equinox conditions.

Verification / Alternative check:
Geography diagrams of Earth's revolution show four key positions: two solstices and two equinoxes. On the equinox diagrams, the Sun's rays are drawn perpendicular to the Equator, with the circle of illumination dividing the Earth into equal halves of day and night. Text descriptions explicitly state that equinox occurs when the Sun is vertically overhead at the Equator. These consistent representations confirm that the Equator is the correct answer.

Why Other Options Are Wrong:
Tropic of Capricorn, at 23.5° south, is the overhead position of the Sun during the December solstice, not during equinoxes.
Tropic of Cancer, at 23.5° north, is where the Sun is overhead during the June solstice, not during equinoxes.
The poles, at 90° latitude, experience polar day or night around solstices and do not have the Sun directly overhead during equinox.

Common Pitfalls:
Students sometimes confuse solstices and equinoxes, thinking that the Sun may be overhead at the tropics during equinox as well. To avoid this, remember: “Equinox = Equator.” Whenever you see the word equinox, link it to equal day and night and the Sun directly above the Equator. Think of solstices instead as the times when the Sun reaches its extreme northern or southern positions over the Tropic of Cancer or Tropic of Capricorn. This simple association will help you answer similar questions quickly.

Final Answer:
An equinox occurs when the Sun is vertically above The Equator, at 0° latitude.