14 thoughts on “December 21, 2018: Darkest”

  1. This reminds me...because we have real (I think) and amateur atronomers amongst us: why do sunrise and sunset times not move symmetrically through the year? Meaning, for example, in June the sunrise plateaus and has zero net change, while sunset gains time and plateaus later. Vice versa in the winter - Sunset time reverses direction in early December, but sunrise doesn't get earlier until January. Referencing standard sunrise/sunset tables like this one.

    1. Because Earth's orbit isn't circular. October has the quickest changes in sunrise/sunset times because it is at its closest to Earth in the orbit. Also, earliest sunset / latest sunrise isn't always on the winter solstice because of one of various wobbles in Earth's spin; can't think of which it is (it's not precession pretty sure)

      1. The faster change in October is not only because of the distance to the Sun; Earth is closest to the Sun on January 4. It’s because of a combination of the elliptical shape of the orbit, along with the way the tilt of the Earth affects the amount of daylight different parts of the Earth gets.

        If the Earth’s orbit was a circle, then the daylight hours would change quickest at the equinoxes, and slowest at the solstices (picture a sine wave). Since the Earth also changes its orbital speed due to its elliptical orbit, those days with the biggest changes gets shifted a bit.

        The earliest sunrise/sunset depend on how the tilt of the Earth’s axis matches up with the direction of the Earth’s elliptical orbit. So it changes (very slowly) due to the precession of the Earths axis and the precession of the Earth’s orbit (aka apsidal precession).

          1. No kidding! Thanks, Mike! Pretty much what I was hoping we’d get, even if I’m going to have to read it a few more times to wrap my head around it all.

              1. Deutsches Wort des Tages

                Innerer Schweinehund Inner pig dog

                It's the only way to get rid of your Kummerspeck.

  2. Homer, Puig, and others on the move.

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