Because the Earth’s orbit is elliptical and takes roughly 365.25 days, the exact start dates change slightly every year, usually falling between the 20th and 23rd of the starting month.
Abstract This paper examines how months align with astronomical and meteorological seasons in both the Northern and Southern Hemispheres, clarifies commonly used conventions, and verifies mappings used in climatology, government reporting, and public communication. It highlights ambiguities arising from differing definitions (astronomical vs. meteorological vs. cultural) and provides a clear, verifiable reference table and short rationale for each convention. months for the seasons verified
: These groupings more closely match the actual temperature patterns observed on Earth. For example, June, July, and August are typically the three warmest months of the year, fitting the logical definition of "summer". Because the Earth’s orbit is elliptical and takes
Because Earth's orbit is an ellipse, not a perfect circle, its speed varies. Earth moves faster when it is closer to the Sun (in January) and slower when it is farther away (in July). This results in astronomical seasons that vary in length from 89 to 93 days. As astronomer Matthew Beaky notes, winter is the shortest season and summer is the longest, "though only by a few days". meteorological vs
Meteorologists divide the year into four three-month periods based on the annual temperature cycle. This system is used for agriculture, commerce, and climate record-keeping because the start dates never change (e.g., March 1st is always the start of spring). Spring: March, April, May Summer: June, July, August Autumn (Fall): September, October, November Winter: December, January, February Southern Hemisphere (e.g., Australia, Brazil, South Africa)
Starts March 19–21; ends June 20–22.