January 19, 2020

AstroEvent of the Week: 15.06.09: The Summer Solstice.

Astronomers throughout the northern hemisphere, rejoice; the long slow onslaught of daylight is about to end! The summer solstice occurs right on schedule this year at 05:45 Universal Time on Sunday, June 21st. The most northerly point in the Sun’s yearly celestial journey, it will now start its long apparent journey south. While this may be the longest (barely) stretch of daylight, don’t confuse it with the earliest sunrise or latest sunset, which may occur weeks prior or after (remember sun-fast and our friend, the Equation of Time?) Now is a good time to note any local Stonehenge- like alignments in your local neighborhood, as the Sun’s path marks the Tropic of Cancer, which actually falls around the Taurus/Gemini border in our modern epoch (sorry to break this to all you astrologer types!)… Here’s to the eventual return of the darkness!

The astro-phrase of the week is Sothic Cycle. Say what? Sounds suitably Lovecraftian, doesn’t it? Like something straight out of the Necronomicon… The Sothic Cycle was used by the ancient Egyptians to mark that all important event (to them)… the helical rising of the Star of Isis, which we know as Sirius. That is, Sirius rose with the Sun, although they generally relied on visual sightings that would fall a week or so later. This coincided with the annual flooding of the Nile. The Sothic Cycle was 1461 modern years long, and owed to the fact the the standard sidereal year is a quarter day longer than 365 days. Thus 365.25 x 4= 1461 years, the time it took for the calendars to come back into sync again. Today, the helical rising of Sirius occurs in early July, but in the Egyptians’ time, it occurred very near the Summer Solstice. The difference is due to the precession of equinoxes, along with the difference in proper motion of both Sirius and our own solar system. The term “Dog Days of Summer,” also derives from the helical rising of Sirius, the “Dog Star…” (get it?) Happy Summer Solstice!

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