December 13th, 2016

The earliest sunset…

…is not at the solstice, the shortest day of the year. It comes somewhat earlier (now, for example), and varies depending on latitude. Here’s an explanation for the phenomenon:

The key to understanding the earliest sunset is not to focus on the time of sunset or sunrise. The key is to focus on what is called true solar noon – the time of day that the sun reaches its highest point, in its journey across your sky.

In early December, true solar noon comes nearly 10 minutes earlier by the clock than it does at the solstice around December 22. With true noon coming later on the solstice, so will the sunrise and sunset times…

The discrepancy occurs primarily because of the tilt of the Earth’s axis. A secondary but another contributing factor to this discrepancy between clock noon and sun noon comes from the Earth’s elliptical – oblong – orbit around the sun.

Read the whole thing.

For example, in Boston this year, the earliest sunset occurs from December 4 to 14, at 4:12 PM. Here’s the chart for Boston.

For me, the earliest sunset days are the darkest days, because I’m not an “up with the lark” person. And the reversal to longer days (that is, to later sunsets) is going to happen very very soon, which makes me happy.

sun

7 Responses to “The earliest sunset…”

  1. Ripple Says:

    Conversely, the latest sunrises in the mid-latitudes occur in early January. Ergo, in late December both sunrises and sunsets are becoming later even as the Solstice is the shortest day of the year.

    When you get down into the tropics, the earliest sunsets become even earlier, i.e., in November. And close to the equator, it’s even stranger, with the times going up and down an additional cycles, although the overall day length changes little.

  2. physicsguy Says:

    Being just SW of Boston in Ct, this is a very depressing time of year for me. I definitely think I have a mild case of SAD. And as I’ve grown older my tolerance of cold and snow has gone way down. New England winters are just not bearable anymore. Retirement in 2 1/2 years and then it’s time to head south.

  3. F Says:

    We lived in Africa, within a few degrees (less than 8 degrees in 3 different countries) for many years. As in 15 years.

    The most noticeable thing about sunset near the equator is that it happens fast. There is no “twilight”. The sun goes down, and 15 minutes later it’s dark.

  4. parker Says:

    Despite years of training as a farm boy and bringing home the bacon, I switched from an early riser to a late sleeper about 15 years ago. Mrs parker wakes me at around 9 am. Early sunsets are not one of my favorite things, but the darkness and cold of winter has aspects that I savor. Winter is a quiet time, there is beauty in the bright blue sky and the clear star filled nights (when they occur), and winter is my favorite time to play chef as warm meals in a warm abode is something to be savor.

    Today it was sunny and the high was 9 with wind chill of minus 4. Tonight it will be minus 4 with wind chill minus 15-20. I do the night time dog walk and it will be cold, quiet, and lots of stars over head. There is beauty to be appreciated in every season.

  5. Yancey Ward Says:

    If you have a globe and a flashlight, you can visually understand it better- it is hard to explain it verbally- at least the effect of the Earth’s tilt on either side of solstice in relation to where a point is on the globe is at sunrise and sunset. I wasn’t aware of the effect of the oblong orbit, and it isn’t something I can even visualize right now- will have to read the article.

    I actually only recently noticed this myself just a few weeks ago when I was trying to determine the length of the day on the Winter Solstice for Oak Ridge. When I looked at the table of sunrise and sunset, it surprised me that the days didn’t shorten and lengthen symmetrically on either side of the date.

  6. Assistant Village Idiot Says:

    Son #4 is in Tromso and hasn’t seen the sun for two weeks. He does say that even on the solstice, you can see some reddening of the sky to the south.

  7. Ken Mitchell Says:

    You can get a table of sunrise/sunset times for your location for an entire year from the US Naval Observatory at http://aa.usno.navy.mil/data/docs/RS_OneYear.php.

    Part of the discrepancy – that the latest sunrises and earliest sunsets don’t align with the winter solstice – is that the Earth is in an elliptical orbit; the Earth is moving fastest at the perihelion, about January 4 each year. Curiously for us Northern Hemisphere denizens, the Earth is closest to the Sun on that date, January 4. (Fortunately, the difference is only about 3%.)

    Winter Blues or “Seasonal Affective Disorder” can be easily treated with a bank of fluorescent lights; get up 30 minutes earlier and sit under the lights. I use a combination of regular tubes and “full spectrum” tubes. Don’t use these in the evening; they’ll prevent you from falling asleep naturally.

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Previously a lifelong Democrat, born in New York and living in New England, surrounded by liberals on all sides, I've found myself slowly but surely leaving the fold and becoming that dread thing: a neocon.
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