PHOENIX — Astronomical spring has many names. It's also called the spring equinox, March equinox or vernal equinox.
Whatever your preference it's officially happening tonight, Tuesday March 19.
VERSIÓN EN ESPAÑOL: ¿Cuál es la diferencia entre la primavera meteorológica y la primavera astronómica?
In the Northern Hemisphere, the sun crosses the celestial equator going south to north. It’s called the “celestial” equator because it’s an imaginary line in the sky above the Earth’s equator. So if you're standing on the equator the Sun would be smack dab overhead.
During this time, the Northern Hemisphere and Southern Hemisphere receive roughly equal amounts of sunlight. The bottom line is neither hemisphere is tilted more toward or away from the Sun than the other.
Remember in most locations, (the North Pole and equator being exceptions), the amount of daylight had been increasing each day after the winter solstice. Now, the amount of daylight each day will continue to increase until the summer solstice in June.
The summer solstice is the day we experience the longest period of daylight.
The word equinox comes from the Latin words for “equal night”— aequus (equal) and nox (night). On the day of the equinox, the length of day and night is nearly equal in all parts of the world.
Astronomically speaking, the first day of spring is marked by the spring equinox, which falls on March 19, 20, or 21. The equinox happens at the exact moment worldwide. However, for the Southern Hemisphere today marks the beginning of fall.
In the meantime, meteorological spring started March 1. Weather scientists divide the year into quarters to make it easier to compare seasonal and monthly statistics from one year to the next.
The meteorological seasons are based on annual temperature cycles rather than on the position of Earth in relation to the Sun, and they more closely follow the Gregorian calendar.
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