By The Associated Press
Spring is here — officially, at least.
The vernal equinox arrives on Tuesday, marking the beginning of the spring season for the Northern Hemisphere.
But what does that actually mean? Here’s what to know about how we divide up the year using the Earth’s orbit.
What is the equinox?
As the Earth moves around the sun, it does so at an angle.
For most of the year, the Earth’s axis is tilted either toward or away from the sun. That means the sun’s warmth and light fall unevenly on the northern and southern halves of the planet.
During the equinox, the Earth’s axis and its orbit align so that both hemispheres receive an equal amount of sunlight. This year, the alignment occurs on March 19 at 11:06 pm Eastern Daylight Time.
The term equinox comes from two Latin words meaning equal and night. That’s because on the equinox, day and night last nearly the same amount of time — though one may get a few extra minutes, depending on where you are on the planet.
The Northern Hemisphere’s spring — or vernal — equinox can occur between March 19 and 21, depending on the year. Its fall – or autumnal — equinox can occur between Sept. 21 and 24.
What is the solstice?
The solstices indicate the times during the year when the Earth is at its most extreme tilt toward or away from the sun. This means the hemispheres are receiving very different amounts of sunlight — and days and nights are at their most unequal.
During the Northern Hemisphere’s summer solstice, the upper half of the earth is tilted toward the sun, creating the longest day and shortest night of the year. This solstice falls between June 20 and 22.
Meanwhile, at the winter solstice, the Northern Hemisphere is leaning away from the sun — resulting in the shortest day and longest night of the year. The winter solstice falls between December 20 and 23.
What’s the difference between meteorological and astronomical seasons?
These are just two different ways to divide up the year.
Meteorological seasons are defined by the weather. They divide the year into three-month seasons based on annual temperature cycles. By that calendar, spring starts on March 1, summer on June 1, fall on Sept. 1 and winter on Dec. 1.
Astronomical seasons depend on how the Earth moves around the sun.
Equinoxes mark the start of spring and autumn. Solstices usher in summer and winter.
The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Science and Educational Media Group. The AP is solely responsible for all content.
