Why meteorological and astronomical winter start on 2 different dates
The December solstice marks the start of winter across the Northern Hemisphere, but meteorologists commonly consider a different date to mark the beginning of the new season.
On the day of the December solstice, the sun's rays are most direct over the Tropical of Capricorn in the Southern Hemisphere. For areas north of the equator, this is the shortest day of the entire year, followed by the longest night.
In 2024, the winter solstice falls on Dec. 21, 2024, at 4:20 a.m. EST.
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Astronomical winter always starts on the solstice, which falls between Dec. 20 and Dec. 22. These dates vary from year to year due to leap years and the elliptical shape of Earth's orbit around the Sun.
While this solstice signals the start of astronomical winter across the Northern Hemisphere, those in the Southern Hemisphere recognize it as the first day of summer.
Traditionally, astronomical seasons last between 89 and 93 days, according to the National Centers for Environmental Information (NCEI). This variability can make it difficult for experts to compare statistics from one year to another.
Meanwhile, meteorological seasons are more consistent, with the four seasons being broken into groups of three months.
Meteorological winter lasts for 91 days every year, starting on Dec. 1 and lasting through the end of February.
•Meteorological winter is December, January and February.
•Meteorological spring is March, April and May.
•Meteorological summer is June, July and August.
•Meteorological fall is September, October and November.
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"By following the civil calendar and having less variation in season length and season start, it becomes much easier to calculate seasonal statistics from the monthly statistics, both of which are very useful for agriculture, commerce and a variety of other purposes," NCEI said.
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