Why is the amount of daylight slightly more than twelve hours at the equinoxes?

Answer 1

This can be explained geometrically. Consider the Sun's apparent path in the sky. If (for example) you live north of the equator, in winter more than half of this path is below the horizon - thus, the night is longer than the day. In summer it's the other way round - more than half of this path is above the horizon. At the equinoxes (approximately March 21, and September 23), half of this apparent path is above the horizon, and half is below the horizon.

Please note that this is only approximate; due to the diameter of the Sun, combined with atmospheric refraction, at the exact day of the equinox the day is slightly longer than 12 hours.

Answer 2

At the equinoxes, the Earth's axis is tilted neither toward nor away from the sun, resulting in an equal amount of day and night. However, due to the way sunlight bends in the Earth's atmosphere, the days are slightly longer as the sun appears to rise before it is geometrically above the horizon and set after it is geometrically below the horizon.

Answer 3

This is the time when the sun crosses the plane of the earth's equator, ie., the ecliptic. These dates are known as the vernal and winter equinoxes.