Changing of the Seasons: Astronomical vs. Meteorological

Updated on March 19, 2018
Bob Bamberg profile image

Earth science is one of Bob's interests and while he mostly writes about animals, this article explores biological control of gypsy moths.


As I write this, we in the northern hemisphere are poised to welcome spring. It arrives on March 20, 2018 at 12:15 P.M. EDT. That’s when the sun crosses the equator on its journey to the Tropic of Cancer, which will usher in the summer season. The southern hemisphere experiences the same thing, but they’re welcoming autumn and saying goodbye to those lazy, hazy, crazy days of summer. For them, it’s the autumnal equinox. It happens at the same time worldwide, but the different time zones will dictate at what time spring or autumn arrives in any given locale.

The sun doesn’t actually cross the equator, of course. Because of the tilt of the earth on its axis (23.5 degrees for those of you keeping count) we actually cross under the sun, baring our equator to our benevolent star. For those of you who can stand at the equator, the sun will be directly overhead when spring arrives. We all enjoy about equal hours of daylight and darkness on the first day of spring.

The sun is directly over the equator at the arrival of the vernal and autumnal equinoxes.
The sun is directly over the equator at the arrival of the vernal and autumnal equinoxes. | Source

Spring doesn’t always arrive on the same day every year. That’s because our orbit around the sun is elliptical, not circular, and because it takes 365.24 days for the earth to complete one orbit of the sun, requiring a day to be added every fourth year (Leap Year). So the arrival of spring varies by a day or two from year to year, fluctuating from March 19th to the 21st. That’s according to the astronomers.

Meteorologists See The Seasons Differently

Meteorological spring arrives about three weeks before astronomical spring, on March 1. Meteorological summer begins on June 1, meteorological autumn begins on September 1, and meteorological winter begins on December 1. Meteorologists and climatologists divide the year into four seasons, each of roughly three months duration, and more closely aligned to our civil calendar than are the astronomical seasons. In a non Leap Year, meteorological winter lasts 90 days while meteorological spring and summer last 92 days.

Weather professionals recognize winter to be the coldest time of the year and summer to be the hottest time of the year. Spring and autumn are considered transitional seasons. Meteorologists and climatologists find it much easier to compile monthly and seasonal weather statistics by dividing the season according to annual temperature cycles and the calendar instead of using the astronomical seasons.

 Weather data is critical to aviation.
Weather data is critical to aviation. | Source

The data compiled by weather scientists is an indispensible tool for many of the world’s industries. Largely dependent upon the weather are agricultural, transportation, tourism, and sports interests. Add to that: municipalities (from plowing roads to maintaining playgrounds), the military, construction, and commerce, and it’s a start.

Each earth year is comprised of two equinoxes (vernal and autumnal), discussed previously, and two solstices (summer and winter). Astronomical summer occurs when the sun “arrives” at the Tropic of Cancer, resulting in the longest day of the year (usually around June 21). Astronomical winter occurs when the sun “arrives” at the Tropic of Capricorn, resulting in the shortest day of the year (usually around December 21).

Most of the world goes by the astronomical seasons: vernal equinox (around March 21), summer solstice (around June 21) autumnal equinox (around September 21) and winter solstice (around December 21). But for meteorologists and climatologists, the seasons change on March 1, June 1, September 1 and Dec. 1.


National Oceanographic and Atmospheric Administration

National Centers for Environmental Information:

Meteorological Versus Astronomical Seasons

Questions & Answers


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      • Bob Bamberg profile imageAUTHOR

        Bob Bamberg 

        16 months ago from Southeastern Massachusetts

        Nice to see you, Heidi, and glad the hub cleared things up. Thanks for taking the time to read and comment.

      • heidithorne profile image

        Heidi Thorne 

        16 months ago from Chicago Area

        I was surprised that one of our local weathermen said March 1 was the first day of spring on the newscast. I always thought it was around mid-March. Now I get it. Thanks for sharing and have a great week!

      • Bob Bamberg profile imageAUTHOR

        Bob Bamberg 

        16 months ago from Southeastern Massachusetts

        I Googled manioc root... I think I would rather stick to potatoes. It's apparently in the cassava family, so you should have skin as smooth as a baby's butt.

      • DrMark1961 profile image

        Dr Mark 

        16 months ago from The Atlantic Rain Forest, Brazil

        French fries, mmm! Most of the villagers grow manioc root since it is adapted to our weather down here, but I have some Irish blood so I need those potatoes. And French fries, mmm!!!!

      • Bob Bamberg profile imageAUTHOR

        Bob Bamberg 

        16 months ago from Southeastern Massachusetts

        Hi Doc, We had a 14.5 inch snowfall last week, 12 days after the arrival of meteorological spring...and tomorrow astronomical spring arrives...1 day before another predicted significant snowfall on Wednesday. Me thinks Mom Nature has her equinoxes and solstices mixed up.

        Sorry to hear about the Atlantic Brazilian Rain Forest potato famine. Maybe you can pick up a peck from Amazon (the e-commerce platform, not the river). For lunch today, I'll have some French fries in your honor! Thanks for stopping by and commenting...always nice to have you drop in.

      • DrMark1961 profile image

        Dr Mark 

        16 months ago from The Atlantic Rain Forest, Brazil

        March 1st has come and gone but it still does not feel like fall down here! I planted some potatoes since I follow the climatologists, not the astronomers, but we had some really hot weather last week and they all wilted and died. I guess I need to wait for our meteorological winter. (If I have not wilted, dried up and blown away by then!!!)


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