# Why the asymmetry between the dates of earliest and latest sunsets (with respect to the solstices)? **URL:** \ **Category:** Factual Questions\ **Created:** [May 17, 2020, 12:13am UTC](https://boards.straightdope.com/t/why-the-asymmetry-between-the-dates-of-earliest-and-latest-sunsets-with-respect-to-the-solstices/853952 "2020-05-17T00:13:13Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [May 17, 2020, 12:13am UTC](https://boards.straightdope.com/t/why-the-asymmetry-between-the-dates-of-earliest-and-latest-sunsets-with-respect-to-the-solstices/853952/1 "2020-05-17T00:13:13Z")
The earliest sunset around here (Toronto) is about 10 or 11 days before the winter solstice. On the other hand, the latest sunset occurs only three or four days after the summer solstice. There is an a symmetry here that I wouldn’t have expected. How does it arise? Thanks. ---
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [May 17, 2020, 12:20am UTC](https://boards.straightdope.com/t/why-the-asymmetry-between-the-dates-of-earliest-and-latest-sunsets-with-respect-to-the-solstices/853952/2 "2020-05-17T00:20:00Z")
> [@KarlGauss](#): > > The earliest sunset around here (Toronto) is about 10 or 11 days before the winter solstice. > > On the other hand, the latest sunset occurs only three or four days after the summer solstice. > > There is an a symmetry here that I wouldn’t have expected. How does it arise? > > Thanks. Just to be clear, there is an asymmetry. ---
**Author:** ![glowacks](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/glowacks/32/5548_2.png) [@glowacks](https://boards.straightdope.com/u/glowacks)\ **Post date:** [May 17, 2020, 12:34am UTC](https://boards.straightdope.com/t/why-the-asymmetry-between-the-dates-of-earliest-and-latest-sunsets-with-respect-to-the-solstices/853952/3 "2020-05-17T00:34:20Z")
The Earth’s orbit is not a perfect circle, and the perihelion and aphelion do not coincide perfectly with the solstices. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [May 17, 2020, 12:46am UTC](https://boards.straightdope.com/t/why-the-asymmetry-between-the-dates-of-earliest-and-latest-sunsets-with-respect-to-the-solstices/853952/4 "2020-05-17T00:46:08Z")
Did you take into account the Equation of Time? ---
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [May 17, 2020, 12:53am UTC](https://boards.straightdope.com/t/why-the-asymmetry-between-the-dates-of-earliest-and-latest-sunsets-with-respect-to-the-solstices/853952/5 "2020-05-17T00:53:50Z")
> [@glowacks](#): > > The Earth’s orbit is not a perfect circle, and the perihelion and aphelion do not coincide perfectly with the solstices. But could this explain a seven day difference? > [@DPRK](#): > > Did you take into account the Equation of Time? No, but again, should it introduce such a substantial asymmetry? Maybe I need to see an orrery or something. ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [May 17, 2020, 1:06am UTC](https://boards.straightdope.com/t/why-the-asymmetry-between-the-dates-of-earliest-and-latest-sunsets-with-respect-to-the-solstices/853952/6 "2020-05-17T01:06:27Z")
Here’s an explanation from our Bad Astronomer: > **[Today is the solstice, the shortest day of the year... so why isn't it the...](https://www.syfy.com/syfy-wire/today-is-the-solstice-the-shortest-day-of-the-year-so-why-isnt-it-the-earliest-sunset)** > > If the December solstice is the shortest day of the year, why doesn't it have the latest sunrise and earliest sunset? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 17, 2020, 1:12am UTC](https://boards.straightdope.com/t/why-the-asymmetry-between-the-dates-of-earliest-and-latest-sunsets-with-respect-to-the-solstices/853952/7 "2020-05-17T01:12:01Z")
Several days isn’t as big an asymmetry as you thing. Around the solstices, the change in sunset (or sunrise) times and locations from one day to the next is only very slight: In fact, with naked-eye observations, it’s difficult to pin down the date of the solstice more precisely than within a week or so. So even a small change in sunset times due to the eccentricity of the Earth’s orbit can shift the date of latest/earliest sunset/rise by several days. ---
**Author:** ![Twoflower](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/twoflower/32/22_2.png) [@Twoflower](https://boards.straightdope.com/u/Twoflower)\ **Post date:** [May 17, 2020, 1:21am UTC](https://boards.straightdope.com/t/why-the-asymmetry-between-the-dates-of-earliest-and-latest-sunsets-with-respect-to-the-solstices/853952/8 "2020-05-17T01:21:10Z")
> [@DPRK](#): > > Did you take into account the Equation of Time? This. It’s not sunrise/sunset that are asymmetrical. It’s that 24:00 hours is the _average_ length of a day, not the exact length of every day. The amount that clock time is ahead or behind solar time is what makes the difference. ---
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [May 17, 2020, 1:35am UTC](https://boards.straightdope.com/t/why-the-asymmetry-between-the-dates-of-earliest-and-latest-sunsets-with-respect-to-the-solstices/853952/9 "2020-05-17T01:35:43Z")
> [@Chronos](#): > > Several days isn’t as big an asymmetry as you thing. Around the solstices, the change in sunset (or sunrise) times and locations from one day to the next is only very slight: In fact, with naked-eye observations, it’s difficult to pin down the date of the solstice more precisely than within a week or so. So even a small change in sunset times due to the eccentricity of the Earth’s orbit can shift the date of latest/earliest sunset/rise by several days. The asymmetry is even more pronounced the closer you are to the equator. For example, in Miami, the earliest sunset is about 21 days before the winter solstice and the latest only 9 days after the summer solstice. I guess eccentricity effects are magnified at low latitudes (not that I can visualize it). ---
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [May 17, 2020, 1:43am UTC](https://boards.straightdope.com/t/why-the-asymmetry-between-the-dates-of-earliest-and-latest-sunsets-with-respect-to-the-solstices/853952/10 "2020-05-17T01:43:06Z")
> [@Twoflower](#): > > This. It’s not sunrise/sunset that are asymmetrical. It’s that 24:00 hours is the _average_ length of a day, not the exact length of every day. The amount that clock time is ahead or behind solar time is what makes the difference. Just so I’m clear, does this also explain the asymmetry of the earliest sunset to the latest sunset relative to the solstices (i.e. the number of days before and after the solstices respectively)? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 17, 2020, 1:37pm UTC](https://boards.straightdope.com/t/why-the-asymmetry-between-the-dates-of-earliest-and-latest-sunsets-with-respect-to-the-solstices/853952/11 "2020-05-17T13:37:13Z")
The effect would be bigger at the equator due to the angle that the Sun sets at. Imagine a long-exposure picture of a sunset, so that instead of a tiny dot, the Sun forms a line across the image. At high latitudes, that line will be close to horizontal, just skimming into the horizon. But in the tropics, that line will plunge nearly straight downwards. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [May 17, 2020, 2:27pm UTC](https://boards.straightdope.com/t/why-the-asymmetry-between-the-dates-of-earliest-and-latest-sunsets-with-respect-to-the-solstices/853952/12 "2020-05-17T14:27:59Z")
> [@Chronos](#): > > The effect would be bigger at the equator due to the angle that the Sun sets at. Imagine a long-exposure picture of a sunset, so that instead of a tiny dot, the Sun forms a line across the image. At high latitudes, that line will be close to horizontal, just skimming into the horizon. But in the tropics, that line will plunge nearly straight downwards. The equator is a good example, because the day is roughly 12 hours long year-round, so all you have to consider is the Equation of Time. If you look at its graph, the asymmetry in question becomes apparent, with the maximum value occurring in early November and the minimum value in February. ---
**Author:** ![Freddy\_the\_Pig](https://avatars.discourse-cdn.com/v4/letter/f/a587f6/32.png) [@Freddy\_the\_Pig](https://boards.straightdope.com/u/Freddy_the_Pig)\ **Post date:** [May 17, 2020, 5:45pm UTC](https://boards.straightdope.com/t/why-the-asymmetry-between-the-dates-of-earliest-and-latest-sunsets-with-respect-to-the-solstices/853952/13 "2020-05-17T17:45:45Z")
> [@Twoflower](#): > > It’s that 24:00 hours is the _average_ length of a day, not the exact length of every day. Two factors cause solar day length to be a little more or a little less than 24:00: (1) The “pendulum effect” of a tilted orbit, which makes solar days shorter near the solstices and longer near the equinoxes; and (2) The elliptical orbit, which makes solar days shorter near perihelion (January) and longer near aphelion (July) In winter, the two effects _reenforce_ each other, so you get _really short_ solar days–enough to create, at the mid-latitudes where most of us live, a 10-12 day lag between earliest sunset and the solstice. In summer, the two effects _offset_. The pendulum effect predominates, so you get “somewhat short” solar days–enough to create a 4-6 day lag. ---
**Author:** ![Freddy\_the\_Pig](https://avatars.discourse-cdn.com/v4/letter/f/a587f6/32.png) [@Freddy\_the\_Pig](https://boards.straightdope.com/u/Freddy_the_Pig)\ **Post date:** [May 17, 2020, 5:57pm UTC](https://boards.straightdope.com/t/why-the-asymmetry-between-the-dates-of-earliest-and-latest-sunsets-with-respect-to-the-solstices/853952/14 "2020-05-17T17:57:32Z")
Except that I reversed “shorter” and “longer” in the above. Really long solar days in December, somewhat long ones in June. ---
**Author:** ![GreenWyvern](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/greenwyvern/32/2834_2.png) [@GreenWyvern](https://boards.straightdope.com/u/GreenWyvern)\ **Post date:** [May 18, 2020, 6:26am UTC](https://boards.straightdope.com/t/why-the-asymmetry-between-the-dates-of-earliest-and-latest-sunsets-with-respect-to-the-solstices/853952/15 "2020-05-18T06:26:29Z")
There’s an additional reason that nobody seems to have mentioned so far. A time zone is an hour wide, so the actual local time may be up to half an hour earlier or later than the standard time across the time zone. At one edge of the time zone, your watch says 6:00AM, but the real local time is 6:30AM. At the other edge, your watch says 6:00AM, but the real local time is 5:30AM. ---
**Author:** ![Schnitte](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/schnitte/32/9033_2.png) [@Schnitte](https://boards.straightdope.com/u/Schnitte)\ **Post date:** [May 18, 2020, 8:43am UTC](https://boards.straightdope.com/t/why-the-asymmetry-between-the-dates-of-earliest-and-latest-sunsets-with-respect-to-the-solstices/853952/16 "2020-05-18T08:43:55Z")
> [@GreenWyvern](#): > > There’s an additional reason that nobody seems to have mentioned so far. > > A time zone is an hour wide, so the actual local time may be up to half an hour earlier or later than the standard time across the time zone. > > At one edge of the time zone, your watch says 6:00AM, but the real local time is 6:30AM. At the other edge, your watch says 6:00AM, but the real local time is 5:30AM. True, but that does not explain the phenomenon that the OP is asking about. In the case of Toronto, the discrepancy between standardised zone time and true local solar time is about 16 minutes (Toronto’s time zone is UTC-5, which corresponds to local time on the 75th Western meridian, and its actual longitude is 79° West). It’s as if the OP had to deduct 16 minutes to convert the time indicated by his watch into local solar time. But that discrepany is constant and applies to each day alike, and the OP is only asking about the days of the earliest and latest sunrises. ---
**Author:** ![Mark\_Finn](https://avatars.discourse-cdn.com/v4/letter/m/34f0e0/32.png) [@Mark\_Finn](https://boards.straightdope.com/u/Mark_Finn)\ **Post date:** [May 18, 2020, 12:02pm UTC](https://boards.straightdope.com/t/why-the-asymmetry-between-the-dates-of-earliest-and-latest-sunsets-with-respect-to-the-solstices/853952/17 "2020-05-18T12:02:02Z")
> [@GreenWyvern](#): > > There’s an additional reason that nobody seems to have mentioned so far. > > A time zone is an hour wide, so the actual local time may be up to half an hour earlier or later than the standard time across the time zone. > > At one edge of the time zone, your watch says 6:00AM, but the real local time is 6:30AM. At the other edge, your watch says 6:00AM, but the real local time is 5:30AM. You would expect a time zone to be “an hour” (or 15 degrees) wide, but there are variations. The extreme Eastern time zone range is from Thunder Bay (Ontario) - 89.2477 degrees west, to Blanc Sablon (Quebec) - 57.1313 west. The two are only 3 degrees apart on latitude - so fairly close. The sun sets today (May 18) at 9:35 pm in Thunder Bay, and at 7:40 pm in Blanc Sablon. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [May 18, 2020, 1:18pm UTC](https://boards.straightdope.com/t/why-the-asymmetry-between-the-dates-of-earliest-and-latest-sunsets-with-respect-to-the-solstices/853952/18 "2020-05-18T13:18:17Z")
The time zones aren’t really an issue, albeit confusing things in places observing Summer Time and similar. For the purposes of this question, it may be better to think in terms of local mean solar time. ---
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [May 18, 2020, 8:19pm UTC](https://boards.straightdope.com/t/why-the-asymmetry-between-the-dates-of-earliest-and-latest-sunsets-with-respect-to-the-solstices/853952/19 "2020-05-18T20:19:59Z")
If the earliest sunset comes 10-12 days before the solstice, then the latest sunrise comes about the same number of days after the solstice. As noted above it is the equation of time. The actual solar day is getting shorter as the earth approaches perihelion in early January. Look at [The World Clock (extended version)](https://www.timeanddate.com/worldclock/full.html), find Toronto and examine the times of solar noon (when the sun crosses your local meridian) as you look through the year and you will find your explanation. You know those figure 8 patterns you sometimes see on world globes. They mark the corrections made for solar noon at different times of year. That figure 8 pattern is called the analemma. On the campus of Williams College is a sundial with an analemma shaped pointer that is all set at such an angle that the sundial would read correctly every day of the year (but you had to know which side of the shadow to read and that changed over the course of the year). Unfortunately a tree had grown next to it and it was in the shade. Pity. ---
**Author:** ![slaphead](https://avatars.discourse-cdn.com/v4/letter/s/e9bcb4/32.png) [@slaphead](https://boards.straightdope.com/u/slaphead)\ **Post date:** [June 3, 2020, 2:08pm UTC](https://boards.straightdope.com/t/why-the-asymmetry-between-the-dates-of-earliest-and-latest-sunsets-with-respect-to-the-solstices/853952/20 "2020-06-03T14:08:12Z")
> [@Chronos](#): > > The effect would be bigger at the equator due to the angle that the Sun sets at. Imagine a long-exposure picture of a sunset, so that instead of a tiny dot, the Sun forms a line across the image. At high latitudes, that line will be close to horizontal, just skimming into the horizon. But in the tropics, that line will plunge nearly straight downwards. The equator is a weird place. First time I went somewhere tropical on vacation I discovered that not only was the moon broken and lying on it’s back, dusk was an on/off function rather than a dimmer. I went to the beach to watch the sunset and had to fumble my way back in the dark. Also most of the invertebrates were in the wrong sizes. [Next page](https://boards.straightdope.com/t/why-the-asymmetry-between-the-dates-of-earliest-and-latest-sunsets-with-respect-to-the-solstices/853952.md?page=2)