Vernal equinox
What is the vernal equinox?
When is the vernal equinox?
What is the difference between the spring equinox and vernal equinox?
Vernal equinox, two moments in the year when the Sun is exactly above the Equator; also, either of the two points in the sky where the ecliptic (the Sun’s apparent annual pathway through the sky) and the celestial equator intersect. In the Northern Hemisphere the vernal equinox falls about March 20 or 21, as the Sun crosses the celestial equator going north.
The vernal equinox is not a day when the day and night are equally long. Because daytime is defined from when the Sun breaks the horizon to when it completely sets, the day is longer by the time it takes the Sun to begin setting to when it completely sets. Atmospheric refraction also bends the Sun’s light so there is light even when the Sun is actually below the horizon. However, there is a day called the equilux when day and night are equally long. In both hemispheres it occurs a few days before the vernal equinox and a few days after the autumnal equinox.
In the Southern Hemisphere the equinox occurs on September 22 or 23, when the Sun moves south across the celestial equator. According to the astronomical definition of the seasons, the vernal equinox also marks the beginning of spring, which lasts until the summer solstice (June 20 or 21 in the Northern Hemisphere, December 21 or 22 in the Southern Hemisphere).
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