On what specific calendar dates are day and night of equal duration?
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Answer: C. March 20 and September 23
Explanation
The vernal equinox in March and autumnal equinox in September are the dates when day and night are of nearly equal length. During equinoxes, the Earth's axis is tilted neither toward nor away from the sun, equalizing daylight globally. The word equinox is derived from Latin roots meaning equal night, reflecting this astronomical alignment. Equinoxes occur twice a year when the geometric center of the sun's disk crosses the celestial equator. The tilt of the Earth's rotational axis relative to its orbital plane causes seasonal changes in day length. These transition dates mark the official astronomical beginning of spring in March and autumn in September.
March 21 and December 24 pair an equinox with a winter solstice date, meaning day and night are not equal. January 14 and September 23 combine an arbitrary winter date with an autumn equinox, missing the spring alignment. January 14 and June 22 represent mid-winter and summer solstice periods characterized by extreme day length inequalities.
- Subject
- Everyday Science
- Category
- Everyday Science
- Topic
- —
- Difficulty
- medium
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