Earliest sunset

comes tomorrow, December 8, if you live at latitude 40 north, a few days later if you are farther north. As explained on the December page (54) of Astronomical Calendar 2014 and a bit more thoroughly in the “Sun, Earth, and Seasons” section (33) in Ast. Cal. 2015 (which you may have just received), this event does not coincide with the midwinter solstice of Dec. 21; and whereas daylight is really shortest at the solstice, it can seem shortest at this earliest-sunset date, because we tend to have our eyes shut at sunrise and open at sunset.

I did see sunrise today: sky, sea, and land were all various shades of gray, except that a long slit in the cloud about three degrees above the horizon shone sensationally gold-orange. If I keep seeing sunrises up to mid January, when the latest of them happens, then in that sense that will be my midwinter.

Another event on the calendar, a minor one, is that Jupiter on Dec. 9 becomes stationary – ceases the eastward movement in our sky which had been bringing it toward the star Regulus in Leo – and, because of the tiny curve in Jupiter’s path, the moment when it is nearest to Regulus is on Dec. 8 theoretically at 19 hours Universal Time. This is a kind of “appulse,” or nearest approach of two bodies, but a wide one, more than 7 degrees. Jupiter and Regulus have been the beacons pf the after-midnight sky. The stationary moment is the beginning of Jupiter’s time of greatest prominence which will culminate in its opposition on Feb. 6. And after it resumes eastward motion it will come back and pass Regulus, closely, next August. I recently learned something about Regulus (not the star but the historical person) which I don’t want to relate now.

141208JupRegulus

4 thoughts on “Earliest sunset”

  1. I’ve read that the fact that we have an equation of time (Sun being “faster” or “slower” compared to average noon) results from the tilt of the Earth’s axis, however the fact that the December lobe of the analemma is “larger” than the June lobe results from the eccentricity of Earth’s orbit. In other words, if the Earth’s orbit were a circle, but our axis tilted, there would still be an analemma, but the two lobes would be equally sized. I can’t wait to get AC15 to read Guy’s explanation and see his diagrams!

  2. Goss, the inclination of the Earth’s axis of rotation relative to the plane of her orbit around the Sun also contributes to the equation of time, which quantifies the earliest sunset / Winter solstice / latest sunrise phenomenon. There are moments when I can visualize and understand how this inclination causes noon to come earlier and later through the seasons. But there are more moments when understanding eludes me.

  3. The issue of the earliest sunset not coinciding with the shortest day of the year seems to come up every year. It’s good to see that people notice this discrepancy of the calendar, but hardly anyone realizes that it is a direct result of Earth’s elliptical orbit.

    This phenomenon is important for people to understand because it partially shows how our small planet, with all of us living out our lives glued to it, moves through the vastness of space. Yes, Galileo, the Earth moves.

  4. We’ve seen precious few sunsets as of late due to the overcast, but today we have a clear blue sky. My brother in Seattle is taking advantage of the short days to do some imaging with his telescope, though I can’t remember what. Elephant Trunk, perhaps?

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