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Seasons: Meteorological vs. astronomical

posted Mar 26, 2015, 8:06 AM by Javad Taghia   [ updated Mar 26, 2015, 8:06 AM ]


Meteorological seasons

In order to be consistent and to make forecasting easier, meterologists divide the year into 4 seasons of 3 months each:

  • spring - starting March 1 and ending May 31,
  • summer - starting June 1 and ending August 31,
  • fall (autumn) - starting September 1 and ending November 30, and
  • winter - starting December 1 and ending February 28 (Februrary 29 in a Leap Year).

These seasons are known as meteorological seasons.

Astronomical seasons

Astronomers and scientists on the other hand, use the dates of equinoxes and solstices to mark the beginning and end of seasons in a year.

Like meteorological seasons, there are 4 astronomical seasons in a year:

  • spring - March equinox to June solstice,
  • summer - June solstice to September equinox,
  • fall (autum) - September equinox to December solstice, and
  • winter - December solstice to March equinox.

Equinoxes and solstices

Equinox and solstice illustration
Equinoxes and solstices illustration

Equinoxes and solstices worldwide

Seasons occur because of the 23.5 degree tilt of the Earth's rotational axis - around the June solstice, the Northern Hemisphere is titled towards the sun. This causes summer in the Northern Hemisphere. The Southern Hemisphere on the other hand, is tilted away from the sun and therefore, experiences winter. The opposite occurs around the December Solstice, when the Southern Hemisphere is tilted towards the sun, while the Northern Hemisphere is tilted away.

The solstices and equinoxes, on the other hand are caused by the Earth's orbit around the Sun.

March equinox: The March equinox occurs when the sun crosses the true celestial equator – or the imaginary line in the sky above the Earth’s equator – from south to north on a day between March 20 and 23. In other words, the Sun moves north of the Equator during the March equinox.

June solstice: The June solstice is also referred to as the summer solstice in the Northern Hemisphere and the winter solstice in the Southern Hemisphere. This is the time when the Sun is at its furthest point from the Equator and the Earth’s north pole tilts towards the Sun.

September equinox: The September equinox is also referred to as the autumnal, autumn or fall equinox in the Northern Hemisphere. It is known as the spring or vernal equinox in the Southern Hemisphere. It occurs on a day between September 21 and 24 when the Earth’s axis of rotation is perpendicular to the imaginary line connecting the centers of the Earth and the sun.

December solstice: The December solstice marks the beginning of winter in the Northern Hemisphere, and summer in the Southern Hemisphere. It also sometimes called the winter solstice in the Northern Hemisphere and summer solstice in the Southern Hemisphere. It occurs on a day between December 20 and 23. At this point, the sun appears directly above the Tropic of Capricorn, and the days are shortest at locations north of the Tropic of Cancer. South of the Antarctic Circle the Sun is visible 24 hours per day.

YearMarch EquinoxJune SolsticeSeptember EquinoxDecember Solstice
201021 Mar4:32 AM AEDT21 Jun9:29 PM AEST23 Sep1:09 PM AEST22 Dec10:38 AM AEDT
201121 Mar10:21 AM AEDT22 Jun3:16 AM AEST23 Sep7:04 PM AEST22 Dec4:30 PM AEDT
201220 Mar4:14 PM AEDT21 Jun9:08 AM AEST23 Sep12:49 AM AEST21 Dec10:12 PM AEDT
201320 Mar10:02 PM AEDT21 Jun3:04 PM AEST23 Sep6:44 AM AEST22 Dec4:11 AM AEDT
201421 Mar3:57 AM AEDT21 Jun8:51 PM AEST23 Sep12:29 PM AEST22 Dec10:03 AM AEDT
201521 Mar9:45 AM AEDT22 Jun2:38 AM AEST23 Sep6:20 PM AEST22 Dec3:48 PM AEDT
201620 Mar3:30 PM AEDT21 Jun8:34 AM AEST23 Sep12:21 AM AEST21 Dec9:44 PM AEDT
201720 Mar9:29 PM AEDT21 Jun2:24 PM AEST23 Sep6:02 AM AEST22 Dec3:28 AM AEDT
201821 Mar3:15 AM AEDT21 Jun8:07 PM AEST23 Sep11:54 AM AEST22 Dec9:22 AM AEDT
201921 Mar8:58 AM AEDT22 Jun1:54 AM AEST23 Sep5:50 PM AEST22 Dec3:19 PM AEDT
202020 Mar2:50 PM AEDT21 Jun7:43 AM AEST22 Sep11:31 PM AEST21 Dec9:02 PM AEDT
* All times are local time for Sydney. Dates are based on the Gregorian calendar. Times adjusted for DST if applicable. Current year is highlighted.

The Seasons Calculator shows the times and dates of Vernal (Spring) & Autumnal (Fall) equinoxes and Summer and Winter solstices all over the world.

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