How are the months in a year divided in to four seasons?

Answer 1

Rather surprisingly, this has become a somewhat controversial question in Britain and other countries around the world.

But, the astronomical seasons are based around the dates of the equinoxes and solstices.

There are two equinoxes (when the day and night are of equal length) these are around the 21st March and 21st September.

There are two solstices (the date of longest daylight and the date of shortest daylight), these are around 21st June and 22nd December.

Astronomically, the seasons change on these dates - so, in the Northern hemisphere, the 21st March is the first day of spring, 21 June the first day of summer, 21st September the first day of autumn, 22 December the first day of winter.

Meteor-logically, the dates are more arbitrarily chosen. In the UK, the met office have chosen the 1st March as the first day of spring, the 1st June summer starts, 1 September autumn, 1 December winter starts (this is a matter of some dispute).
Jan through March are summer, April through June are autumn, July through September are winter, and October through December are spring. In the temperate part of the Southern Hemisphere.

Six months different in the temperate part of the northern hemisphere.

These concepts are inappropriate in the polar and the tropical regions.

Answer 2

That depends on where you are.

In Northern Scandinavia the Lapps have eight seasons. Most of the rest of Europe has four.

I Sweden there is a meteorological definition of the seasons (for example when the temperature trend is rising and as much above as below 10° C it is called summer! That would not do in Mexico!)

During the period 1961 to 1991, summer came to various parts of Sweden between the 5th of May and 5th of July.