When seasons commence, and their duration, are defined in different ways and are used for different reasons:
Astronomical seasons are based on the position of the Earth in relation to the Sun. The rotation of Earth around the Sun forms the basis for the astronomical calendar in which seasons are defined with two solstices and two equinoxes. Earth’s tilt and the Sun’s alignment over the equator determine both the solstices and equinoxes.
Meteorological seasons are based on the annual temperature cycle. Meteorologists and climatologists break the seasons down into groupings of three months based on the annual temperature cycle as well as the Gregorian calendar. In the southern hemisphere, meteorological autumn includes March, April, and May; meteorological winter includes June, July, and August; meteorological spring spans September, October, and November; and meteorological summer is over December, January, and February.
People have used observable natural phenomena to mark time for thousands of years. Phenology is the study of cyclic and seasonal natural phenomena, especially in relation to climate, plant and animal life. Depending on where you are in the world different phenological markers can be used to define the seasons, such as when the first leaf falls, the first frost or the first spring growth.
Seasonal cycles as described by the various Aboriginal cultures differ substantially according to location. Natural barometers are not uniform across the land so the reaction of plants and animals are used to gauge what is happening in the environment and the names of seasons are often dependent on localised events or resources.
Exmouth, Western Australia
Image credit: Lisa Mitchell