Thursday, June 20, 2024

Summer Solstice

Today is the Summer Solstice (in the Northern Hemisphere). It'll happen at 20:51 UTC (1:51 PM PST or 4:51 PM EST). 

But what is a "solstice"? Well, "sol" is Latin for the sun. The actual name of the sun is "Sol." "Stice" come from Latin to make stand, or stop. So it means "sun stopping." The same root, by the way, is used in armistice. That is, arms (weapons) standing.

The summer solstice is when the sun stops moving north. It halts its northern progress at the Tropic of Cancer. On the Summer Solstice it is directly overhead of the Tropic of Cancer. This is partially how Eratosthenes measured the circumference of the Earth in 240 BC with surprising accuracy.

This Summer Solstice is the earliest in 228 years. And over the next 72 years, the solstice will get progressively earlier every four years. This happens not because of some cosmological reason, but how we humans measure time. Our calendar does not exactly line up with astronomical events. 

Read more in depth about it here.

Some people call the Summer Solstice "the longest day." This is not exactly accurate. The day is still (pretty close to) 24 hours long. What it is is that, in the Northern Hemisphere, it is the day with the most hours of daylight. How much daylight depends on your latitude. The farther north you are, the more daylight you will have. If you are at or above the Arctic Circle, you'll have at least one day where the sun never sets. 

Some people ascribe special meaning to the solstice. But it really means nothing more than the tilt of the Earth's axis causing the seasons. On the summer solstice, the axis is leaning toward the sun at the north (and away at the south). 

Do you have any plans for the summer solstice? Let me know in the comments below.

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