Meteorological summer vs. astronomical summer explained
When does summer officially begin? That may seem like a simple question, but there are three possible answers.
The changing seasons are based on Earth’s position in its orbit around the sun, the astronomical season. There’s another type of season used by meteorologists known as the meteorological season.
Memorial Day weekend is often touted as the unofficial start of summer across the United States, but the first official day of summer differs between weather forecasters and astronomers.
Typically, the June solstice is considered to be the official start to summer in the Northern Hemisphere with the season lasting until the autumnal equinox in September. The exact dates and times of the solstice vary year to year due to the Earth's imperfect orbit around the sun, but the solstice usually falls on June 20 or June 21, followed by the equinox on Sept. 22 or Sept. 23.
In 2025, the solstice occurs on Friday, June 20, at 10:42 p.m. EDT, marking the start of astronomical summer. The season ends 93 days later on Sept. 22 at 2:19 p.m. EDT.
The sun rises at Stonehenge, near Amesbury, in Wiltshire, southern England on June 21, 2023, during the Summer Solstice festival. (Photo by DANIEL LEAL/AFP via Getty Images)
However, not everyone follows the same seasonal guidelines.
Weather forecasters view the seasons a little differently, consulting the calendar to determine the start of a new season rather than looking to Earth's orbit around the sun.
"Meteorologists and climatologists break the seasons down into groupings of three months based on the annual temperature cycle as well as our calendar," NOAA explained.
Meteorological summer is exactly three months long and starts on June 1 and lasts through Aug. 31 every single year.
"The length of the meteorological seasons is also more consistent," according to NOAA. "It becomes much easier to calculate seasonal statistics from the monthly statistics, both of which are very useful for agriculture, commerce, and a variety of other purposes."
Solar summer is one of the lesser-known definitions of the season and is centered around the three-month period when the most amount of sunlight reaches the Northern Hemisphere. This takes place from May through July with the solstice occurring at the midpoint of the season.
There is one more way to define summer, and it is not based on our sun or the calendar but rather on a star that is nearly 6 trillion miles away from Earth.
Sirius is the brightest star in the night sky and has the nickname of the dog star.
Between July 3 and Aug. 11, Sirius is in the same part of the sky as the sun, a time of the year that is known as the "dog days of summer."
It was once believed that the added starlight from Sirius, in tandem with the light from our sun, made this six-week period the hottest stretch of the entire summer.
While this is not the case, and the light from Sirius does not impact the temperature on Earth, the nickname has stuck around and is still used by meteorologists and the general public today.
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