Technically speaking, the summer solstice occurs when the sun is directly over the Tropic of Cancer, or 23.5° north latitude. This occurred at exactly 6:07 am Eastern on Thursday the 21st. So set your alarm, or feel free to sleep right through it.
Below is a short scientific guide to the longest day of the year. (Though not, as we’ll see, the longest day in Earth’s history — that happened back in 1912.):
- Why do we have a summer solstice, anyway?
- How many hours of sunlight will I get on Thursday?
- Is the solstice the latest sunset of the year?
- What does all this have to do with Stonehenge?
- Is this the longest day in Earth’s entire history?
- I clicked this article accidentally and really just want a cool picture of the sun
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What is a Solstice?
A solstice is one of the two times of the year when the positioning and tilt of Earth relative to the sun results in the most amount of daylight time or the least amount of daylight time in a single day. There are two solstices during the year: one that occurs around June 20–22 (usually June 20 or 21) and one that occurs around December 20–23 (usually December 21 or 22).
The solstices are traditionally considered to mark the start of summer and winter. But which season begins with each solstice depends on which hemisphere you’re in. In the Northern Hemisphere, the summer solstice occurs in June and the winter solstice occurs in December. In the Southern Hemisphere, it’s the opposite. The summer solstice results in the longest day of the year, meaning it has the most time of daylight, and the winter solstice results in the shortest day of the year, meaning it has the longest period of darkness.
In contrast, an equinox is one of the two times of the year when the amount of daylight and nighttime hours are just about of equal length. The two equinoxes occur around March 20–21 and September 22–23. In the Northern Hemisphere, the vernal equinox (or spring equinox) occurs in March and the autumnal equinox occurs in September. In the Southern Hemisphere, it’s the opposite.
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