Editor’s note: This story has been updated to correct the date of winter solstice.
(WHTM) – A quick look at the calendar shows the first day of spring, landing in mid-March, is right around the corner. But, did you know it also starts on March 1?
No, you didn’t read that wrong. There are two types of spring that start at two different times. There’s the astronomical spring and the meteorological spring.
A question many meteorologists get is why are there two and if is there a difference.
According to the National Centers for Environmental Information, the astronomical seasons have been used to make time for thousands of years. The rotation of the sun forms the basis of the astronomical calendar.
The Earth’s tilt and the sun’s alignment over the equator determine both the solstices and the equinoxes. Equinoxes mark the times when the sun passes directly over the equator of the northern hemisphere. The astronomical seasons are:
- Spring Equinox: Around March 21
- Summer Solstice: Around June 21
- Autumnal Equinox: Around September 22
- Winter Solstice: Around December 22
These seasons are reversed when it comes to the southern hemisphere.
NOAA states that the elliptical shape of Earth’s orbit around the sun causes the lengths of the astronomical seasons to vary between 89 and 93 days. These variations in season length and season start would make it very difficult to consistently compare climatological statistics for a particular season from one year to the next.
That’s when the meteorological seasons come into the picture.
The meteorological seasons allow meteorologists and climatologists to break the seasons up into four groups of three months based on the annual temperature cycle, as well as the calendar. The meteorological seasons do not change or vary by year. Those seasons are:
- Spring: March 1 to May 31
- Summer: June 1 to August 31
- Autumn: September 1 to November 30
- Winter: December 1 to February 28 (or Februar 29 during a leap year)
Observing and forecasting led to the creation of the meteorological seasons. They are also easier to remember, ranging from 90 days for winter of a non-leap year to 92 days for spring and summer.
This also makes it easier to figure out our seasonal statistics from the monthly statistics, both of which are very useful for agriculture, commerce, and a variety of other purposes.