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When is the midpoint of winter?

An image of Earth taken by Suomi NPP Satellite
An image of Earth taken by Suomi NPP Satellite (Image credit: NASA)

Every year on Feb. 2, the U.S. mainstream media focuses its attention on the little community of Punxsutawney, Pennsylvania, to see if a groundhog named Phil, emerging from his burrow on Gobblers Knob, will either see his shadow (meaning winter will persist for six more weeks) or does not see his shadow (foretelling an early spring). 

On many calendars, this is also known as Candlemas, the "40th day of Christmas" (that is, of a period which includes Christmas as its first day). The legend of the groundhog likely originated from this axiom about Candlemas:

"If Candlemas be fair and bright, come, winter, have another flight;
If Candlemas brings clouds and rain, go, winter, and not come again."

In spite of the fact that Punxsutawney Phil is revered by many as a weather forecaster, the truth of the matter is, his prognosticating abilities are something less than to be desired. 

In fact, you'd probably do better just tossing a coin.

The first quarter 

On the ancient Celtic calendar, the beginning of each season was considered to be a "quarter day," while the midpoint of a particular season was considered to be a "cross-quarter day," according to The Old Farmer's Almanac. Traditionally, Candlemas or Groundhog Day is the first cross-quarter day of the year; it has also been considered the midpoint of the winter season.

Or is it?

Actually, considering what you would consider the midpoint, we can provide two possible answers: 

First, there is the chronological midpoint that is based solely on our Gregorian Calendar. According to the highly reputable astronomical calculator Jean Meeus, since the year 1246, winter is the shortest season and currently lasts about 88.98 days in length. 

The recent winter solstice occurred Dec. 21 at 10:59 a.m. EST (1559 GMT), while the vernal equinox is set to occur March 20 at 11:33 a.m. EDT (1533 GMT), taking U.S. daylight saving time into account. The midpoint between these two dates and times works out to be Feb. 3 at 10:46 a.m. EST (1546 GMT)

Astronomers, however, calculate the dates and times of the start of each season based on Earth's heliocentric longitude; the precise longitude of a celestial body (in this case, the Earth) as if seen from the center of the sun. 

In this case, at the moment of the winter solstice, Earth is at heliocentric longitude 270 degrees, while at the moment of the vernal equinox it is at heliocentric longitude 0 degrees. The midpoint between these two values is 315 degrees, and Earth did not reach that point in its orbit until Feb. 3 at 3:51 p.m. EST (2051 GMT).

The reason for the five-hour difference stems from the fact that the Earth does not move around the sun in a perfect circle, but rather in an elliptical orbit. We are closest to the sun in early January; hence it moves more rapidly at this particular point in its orbit. It is also for this reason that winter is the shortest of the four seasons and why Earth also arrives at the midpoint of the winter season based on its unambiguous position in its orbit just a bit earlier as opposed to calendrical variations. 

But regardless of what time scale you care to use, winter's midpoint in 2022 — contrary to the tradition of Candlemas or the annual extended forecast derived by Punxsutawney Phil — is Feb. 3. 

So, depending on your point of view — someone who is already "Febru-weary" of winter or someone who is anxiously looking forward to spring — your seasonal weather glass is either half empty or half full.

Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmers' Almanac and other publications. Follow us on Twitter @Spacedotcom and on Facebook. 

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Joe Rao
Joe Rao

Joe Rao is Space.com's skywatching columnist, as well as a veteran meteorologist and eclipse chaser who also serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmers' Almanac and other publications. Joe is an 8-time Emmy-nominated meteorologist who served the Putnam Valley region of New York for over 21 years. You can find him on Twitter and YouTube tracking lunar and solar eclipses, meteor showers and more. To find out Joe's latest project, visit him on Twitter.