Summer can start in different ways depending on the definition:
- Astronomical summer begins on the summer solstice , which occurs around June 20 or 21 in the Northern Hemisphere. For example, in 2025, astronomical summer starts on June 21. This is when the Earth's North Pole is tilted most directly toward the Sun, resulting in the longest day of the year.
- Meteorological summer is based on the calendar and always begins on June 1 and lasts until August 31. It divides the year into four fixed three-month seasons for easier weather observation and statistics comparison.
So, summer starts either on June 1 (meteorological) or June 20/21 (astronomical) in the Northern Hemisphere. In the Southern Hemisphere, summer starts around December 21/22, aligned with their summer solstice.
In short:
Definition| Northern Hemisphere Start Date
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Astronomical summer| June 20 or 21 (Summer Solstice)
Meteorological summer| June 1
This explains why people may refer to different start dates for summer.
