Summer 2021 in United States

Summer Starts: Sunday, Jun 20 8:32 pm PDT

Summer Ends: Wednesday, Sep 22 12:21 pm PDT

Region: California/United States

The first day of summer (June solstice) is when the sun is in its most northern position directly over the Tropic of Cancer. This is referred to as astronomical summer or the summer solstice.

Astronomical summer starts at different times around the planet because of the different time zones as related to Coordinated Universal Time (UTC, same as Greenwich Mean Time based on the Royal Observatory in Greenwich, London [1]). For countries located west of UTC your summer will start earlier than countries located east of UTC.

Astronomical and Meteorological Summer

Astronomical Summer is determined by the changing positions of the earth relative to the sun giving us the solstices and equinoxes. Seasons are caused by the tilt of the earth on its axis by 23.5 degrees. The tilt of the earth does not change as it goes around the sun so in the Northern Hemisphere the earth is tilted toward the sun in June and away from the sun in December[2]. When the sun is over the equator you have the equinoxes and when the sun is over the Tropic of Cancer in the most northern position you have the summer solstice and conversely when the sun is over the most southern position over the Tropic of Capricorn you have the winter solstice. The summer solstice occurs in the Northern Hemisphere between the dates of June 20 to 22 followed by the September equinox - September 21 to 23 and then the Winter solstice - December 20 to 23 and finally the March equinox - March 19 to 21. The United States, most of North America, Europe and many countries in the Northern Hemisphere use astronomical summer to determine when summer season officially starts and ends.

Meteorological Summer is determined by the annual temperature cycles and the Gregorian calendar. Meteorological summer starts June 1st in the Northern Hemisphere and lasts 3 months (June, July, and August) with Autumn Season (September, October, and November) and Winter Season (December, January, and February) and finally Spring Season (March, April, and May). Australia and New Zealand in the Southern Hemisphere use meteorological summer thus the months of December, January, and February to determine their summer season.

Many countries around the world depending on their latitude will use different methods to determine the start of summer. Some of these methods are dependent on the longest day measured, cultural festivals, temperatures and traditional calendar systems. More of these timing methods to determine summer can be found on Wikipedia.org.

References:
1.”Greenwich Mean Time” - Wikipedia, wikipedia.org.
2.”Earths tilt and Seasons” - National Oceanic and Atmospheric Administration, noaa.gov.

Dates for Summer

Year	Summer Starts	Summer Ends
Summer 2024	Thursday, June 20 2024	Sunday, September 22 2024
Summer 2025	Friday, June 20 2025	Monday, September 22 2025
Summer 2026	Sunday, June 21 2026	Tuesday, September 22 2026
Summer 2027	Monday, June 21 2027	Wednesday, September 22 2027
Summer 2028	Tuesday, June 20 2028	Friday, September 22 2028
Summer 2029	Wednesday, June 20 2029	Saturday, September 22 2029