The first day of meteorological spring is March 1. Astronomical spring, on the other hand, begins March 20.
Confused? You’re not alone.
Here are some things to know about the two seasons:
What’s the difference?
According to the National Oceanic and Atmospheric Administration, meteorologists follow the meteorological seasons based on the annual temperature cycle, whereas climatologists follow astronomical seasons, which are defined by the Earth's position in relation to the sun.
What are solstices and equinoxes?
Astronomical seasons are defined with two solstices and two equinoxes.
According to the National Weather Service, the summer solstice occurs the moment the earth's tilt toward the sun is at a maximum and when the sun is directly over the Tropic of Cancer. The sun is at its highest point in the sky anywhere north of the Tropic of Cancer. This is the longest day of the year in those areas.
The winter solstice occurs when the sun is directly over the Tropic of Capricorn and marks the shortest day and longest night of the year.
Equinoxes, on the other hand, are times of the year when the earth’s axis is tilted neither toward nor away from the sun. On these days, there’s almost an equal amount of daylight and darkness at all latitudes. But days are a little longer at the higher latitudes.
Approximately when do the solstices and equinoxes occur in the northern hemisphere?
[Note: Days vary slightly per year; Use this form to calculate dates for a specific year.]
Summer solstice: June 21
Winter solstice: Dec. 21
Vernal/spring equinox: March 20
Autumnal equinox: Sept. 23
When does astronomical spring begin?
Astronomical spring begins on the vernal or spring equinox, around March 21. (In 2019, spring begins March 20.)
Which do we typically use to define seasons?
While people have long used the sun’s alignment and other natural phenomena to mark time, meteorological seasons are more closely tied to our calendar than the astronomical seasons. For example, meteorological spring includes March, April and May. Summer includes June, July and August. Fall includes September, October and November. And lastly, winter includes December, January and February.
Meteorological seasons are also more consistent compared to astronomical seasons.
Why do we typically use meteorological seasons for our civil calendars?
The exact dates of the solstices and equinoxes can vary between 89-93 days due to the earth’s elliptical orbit and whether or not it’s a Leap Year.
Due to the consistency of meteorological seasons (each season is roughly 90-92 days long), calculating seasonal statistics from monthly numbers is much easier. According to NOAA, this data is often used to understand trends in agriculture, commerce and more.
Learn more about the seasons at ncei.noaa.gov.
Credit: Christopher Furlong
Credit: Christopher Furlong
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