What is the difference between astronomical and meteorological spring?
Editor’s note: This story has been updated to correct the winter solstice date.
(WHTM) — A quick glance at the calendar shows that the first day of spring, landing in the middle of March, is just around the corner. But, did you know that it also starts on March 1?
No, you didn’t read this wrong. There are two types of spring that start at two different times. There is an astronomical spring and a meteorological spring.
The question many meteorologists ask is why are there two and if there is a difference.
According to the National Centers for Environmental Information, astronomical seasons have been used to measure time for thousands of years. The rotation of the Sun forms the basis of the ephemeris.
The Earth’s tilt and the Sun’s alignment above the equator determine both the solstices and the equinoxes. The equinoxes refer to the times when the sun passes directly over the equator in the northern hemisphere. The astronomical seasons are:
- Spring Equinox: Around March 21st
- Summer solstice: around June 21st
- Autumnal equinox: around September 22nd
- Winter solstice: around December 22nd
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 astronomical seasons to vary between 89 and 93 days. These differences in season length and early season would make it very difficult to consistently compare climatic statistics for a given season from year to year.
That’s when meteorological seasons come into the picture.
Meteorological seasons allow meteorologists and climatologists to divide the seasons into four quarterly groups based on the annual temperature cycle, as well as the calendar. Meteorological seasons do not change and they do not change according to the year. Those chapters are:
- Spring: from March 1 to May 31
- Summer: June 1 – August 31
- Fall: September 1 – November 30
- Winter: December 1 toebruary 28 (orebruary 29 during a leap year)
Observation and forecasting gave rise to the meteorological seasons. They are also easy to remember, ranging from 90 days for winter in a non-leap year to 92 days for spring and summer.
This also makes it easier to learn our seasonal stats than our monthly stats, both of which are very useful for farming, trade, and a variety of other purposes.