Memorial Day weekend is often thought of as the unofficial start of the summer season in the United States, but the first official day of summer is defined differently by forecasters and astronomers.
Typically, the June solstice is considered the official start of summer in the Northern Hemisphere, with the season continuing until the autumn equinox in September. The exact dates and times of the solstice vary each year due to the Earth's imperfect orbit around the Sun, but it typically occurs on June 20 or 21, followed by the equinox on September 22 or 23.
In 2025, the solstice occurs on Friday, June 20, at 10:42 p.m. ET, marking the beginning of astronomical summer. The season ends 93 days later, on September 22, at 2:19 p.m. ET.
However, not everyone adheres to the same seasonal definitions.
Forecasters view the seasons slightly differently, using a calendar to determine the start of a new season rather than observing the Earth's orbit around the Sun.
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“Meteorologists and climatologists divide the seasons into three-month groups based on the annual temperature cycle and our calendar,” NOAA explained.
Meteorological summer lasts exactly three months, starting on June 1 and ending on August 31 of each year.
“The length of weather seasons is also more stable,” NOAA says. “This makes it easier to calculate seasonal statistics from monthly ones, which is useful for agriculture, commerce, and many other areas.”
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Solar summer is one of the lesser-known definitions of the season, which centers around the three-month period when the greatest amount of sunlight reaches the Northern Hemisphere. This period runs from May to July, with the solstice falling halfway through the season.
There is another way to determine summer that is based not on our Sun or calendar, but on a star nearly 6 trillion miles from Earth.
Sirius is the brightest star in the night sky and is called the “dog star”.
Between July 3 and August 11, Sirius is in the same part of the sky as the Sun. This period is known as the “dog days of summer.”
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It was previously thought that the extra light from Sirius, combined with the light from our Sun, made this six-week period the hottest time of the entire summer.
Although this is not true, and the light from Sirius does not affect temperatures on Earth, the name has stuck and continues to be used by both meteorologists and the general public.
Sourse: www.upi.com
