<p>I was very surprised when I first heard this and it took a little while to understand it.</p>
<p>The simple answer is to do with the M in GMT.  This is &quot;mean&quot; in its sense of average.  So, clock noon to the next clock noon is a fixed amount of time: the average day.  If you used a sundial, then you would find that sundial noon to sundial noon was not always the same length.  It is this variation in the length of the sundial day that causes the surprising non-coincidence of shortest day, latest sunrise, and earliest sunset.  If you use a sundial instead of a modern clock then you would not see this surprising behaviour.</p>
<p>As Martin says, look up the <a href="https://en.wikipedia.org/wiki/Equation_of_time" rel="nofollow noreferrer">Equation of time</a> for why the length of the day varies and how it does so.</p>

CC BY-SA 4.0
2020-12-21T11:17:35.533Z
2020-12-21T11:17:35.533Z
badjohn
<p>This is an interesting question which opens up wide vistas! Look up <a href="https://en.wikipedia.org/wiki/Equation_of_time" rel="nofollow noreferrer">the Equation of Time</a> on Wikipedia for a start.</p>
<p>What is your source? I can't find the sunrise and sunset times in Ashland. <a href="https://www.esrl.noaa.gov/gmd/grad/solcalc/table.php?lat=45.52&amp;lon=-122.65&amp;year=2020" rel="nofollow noreferrer">The ESRL site for Ashland</a> gives noon to the second but sunrise and sunset only to the minute.</p>
<p>At present the days are 24 hours and 30 seconds long, so each noon is 30 seconds later, by the clock, than the last one. This &quot;later each day&quot; applies to all solar events including sunset and sunrise, and this is the reason why the sunsets are already getting later each day while the sunrises don't start getting earlier until early January.</p>
<p>What puzzles me is that this does not by itself account for the discrepancy you are seeing <em>in actual sunrise-to-sunset length</em>, which is why I asked about the source.</p>

CC BY-SA 4.0
2020-12-21T13:58:00.860Z
The source is here:https://sunrise-sunset.org/us/ashland-or - scroll down about halfway and you'll find the day length for December.
DevonTaig
CC BY-SA 4.0
2020-12-21T15:21:55.133Z
Wouldn't it apply to the ***derivative*** of equation of time? That is, for example, one day would 24 hours and 30 seconds and the next one 24 hours and 34 seconds. Is that even possible? Can the equation of time change that fast?
Peter Mortensen
CC BY-SA 4.0
2020-12-21T15:29:35.410Z
Yes! According to [this graph](https://en.wikipedia.org/wiki/File:Tijdvereffening-equation_of_time-en.jpg), it changes by about 17 seconds per day in December.
Peter Mortensen
CC BY-SA 4.0
2020-12-21T15:42:01.020Z
Does the sign of the change fit the claim?
Peter Mortensen
CC BY-SA 4.0
2020-12-21T15:51:26.493Z
Wouldn't altitude relative to the surrounding landscape have a significant effect?  If you live in a deep valley between high mountains, your "day" is going to be considerably shorter than if you lived on top of one of those mountains.  If you have high mountains to the east and open ocean to the west (as much of Oregon does), this would significantly offset your sunrise and sunset times.
Darrel Hoffman
CC BY-SA 4.0
2020-12-21T15:56:02.533Z
-1. The discrepancy is not due to the equation of time. The length of daylight is a function of the Sun's declination. Since the Sun's declination is minimum at the winter solstice, the length of day is minimum at the solstice. The equation of time explains why the earliest sunset (Dec 7) and latest sunrise (Jan 4) occur on different dates and neither date is the solstice.
JohnHoltz
CC BY-SA 4.0
2020-12-21T09:46:54.453Z
2020-12-21T09:46:54.453Z
Martin Kochanski
<p>The other possibility is <a href="https://sunrise-sunset.org" rel="noreferrer">https://sunrise-sunset.org</a> is inaccurate.</p>
<ul>
<li>An app that I use, LunaSolCal, show the length of day on Dec 20, 21, and 22 in Ashland OR are 9:05:45, 9:05:44, 9:05:49.</li>
<li>The website <a href="https://www.timeanddate.com" rel="noreferrer">https://www.timeanddate.com</a> does not have Ashland OR in its database, so I used nearby Medford OR. The length of day on Dec 20, 21, and 22 are 9:04:50, 9:04:49, and 9:04:53.</li>
</ul>
<p>Although those two sources have a difference of 1 minute in the length of the day, the pattern is correct and expected: the shortest length of daylight is on the day closest to the winter solstice. Therefore, I think sunrise-sunset.org is off by one day with its calculations.</p>

CC BY-SA 4.0
2020-12-22T13:12:06.653Z
I do believe the site sunrise-sunset.org to be inaccurate. At least for those two days, the error seems to extend well beyond Oregon - I spot checked Boise, Salt Lake City, and Denver and they similarly show the day before the solstice as being the shoetest.
DevonTaig
CC BY-SA 4.0
2020-12-22T17:17:46.187Z
@DevonTaig It's a leap year. Maybe that has something to do with it?
wizzwizz4
CC BY-SA 4.0
2020-12-21T15:51:54.207Z
2020-12-21T15:51:54.207Z
JohnHoltz
<p>Here in Ashland, Oregon, today (Dec 20, 2020) is the shortest day length of the year at 9:05:45.  But the winter solstice isn't until 2:02 AM PST tomorrow (Dec 21, 2020). Tomorrow's day length is a whopping three seconds longer at 9:05:48.  Why is tomorrow's day length greater than today? It would seem to me that tomorrow's sunrise and sunset are slightly closer to the magic moment of winter solstice and should therefore account for a slightly <em>shorter</em> day.</p>

CC BY-SA 4.0
2020-12-21T09:02:33.117Z
Related: https://astronomy.stackexchange.com/q/28058/16685
PM 2Ring
<solstice>
Why is today the shortest day but the solstice is actually tomorrow?
DevonTaig
# Why is today the shortest day but the solstice is actually tomorrow?

(Asked by: username_0 on 2020-12-21)

Here in Ashland, Oregon, today (Dec 20, 2020) is the shortest day length of the year at 9:05:45. But the winter solstice isn't until 2:02 AM PST tomorrow (Dec 21, 2020). Tomorrow's day length is a whopping three seconds longer at 9:05:48. Why is tomorrow's day length greater than today? It would seem to me that tomorrow's sunrise and sunset are slightly closer to the magic moment of winter solstice and should therefore account for a slightly *shorter* day.

**Tags:** solstice

> **Comments:**
> **username_1**: Related: https://astronomy.stackexchange.com/q/28058/16685  

---

## 3 answers

### Answer by username_6 on 2020-12-21. Score: 9 | Accepted answer

The other possibility is <https://sunrise-sunset.org> is inaccurate.

* An app that I use, LunaSolCal, show the length of day on Dec 20, 21, and 22 in Ashland OR are 9:05:45, 9:05:44, 9:05:49.
* The website <https://www.timeanddate.com> does not have Ashland OR in its database, so I used nearby Medford OR. The length of day on Dec 20, 21, and 22 are 9:04:50, 9:04:49, and 9:04:53.

Although those two sources have a difference of 1 minute in the length of the day, the pattern is correct and expected: the shortest length of daylight is on the day closest to the winter solstice. Therefore, I think sunrise-sunset.org is off by one day with its calculations.

> **Comments:**
> **username_0**: I do believe the site sunrise-sunset.org to be inaccurate. At least for those two days, the error seems to extend well beyond Oregon - I spot checked Boise, Salt Lake City, and Denver and they similarly show the day before the solstice as being the shoetest.  
> **username_7**: @username_0 It's a leap year. Maybe that has something to do with it?  

---

### Answer by username_2 on 2020-12-21. Score: 4

I was very surprised when I first heard this and it took a little while to understand it.

The simple answer is to do with the M in GMT. This is "mean" in its sense of average. So, clock noon to the next clock noon is a fixed amount of time: the average day. If you used a sundial, then you would find that sundial noon to sundial noon was not always the same length. It is this variation in the length of the sundial day that causes the surprising non-coincidence of shortest day, latest sunrise, and earliest sunset. If you use a sundial instead of a modern clock then you would not see this surprising behaviour.

As username_3 says, look up the [Equation of time](https://en.wikipedia.org/wiki/Equation_of_time) for why the length of the day varies and how it does so.


---

### Answer by username_3 on 2020-12-21. Score: 3

This is an interesting question which opens up wide vistas! Look up [the Equation of Time](https://en.wikipedia.org/wiki/Equation_of_time) on Wikipedia for a start.

What is your source? I can't find the sunrise and sunset times in Ashland. [The ESRL site for Ashland](https://www.esrl.noaa.gov/gmd/grad/solcalc/table.php?lat=45.52&lon=-122.65&year=2020) gives noon to the second but sunrise and sunset only to the minute.

At present the days are 24 hours and 30 seconds long, so each noon is 30 seconds later, by the clock, than the last one. This "later each day" applies to all solar events including sunset and sunrise, and this is the reason why the sunsets are already getting later each day while the sunrises don't start getting earlier until early January.

What puzzles me is that this does not by itself account for the discrepancy you are seeing *in actual sunrise-to-sunset length*, which is why I asked about the source.

> **Comments:**
> **username_0**: The source is here:https://sunrise-sunset.org/us/ashland-or - scroll down about halfway and you'll find the day length for December.  
> **username_4**: Wouldn't it apply to the ***derivative*** of equation of time? That is, for example, one day would 24 hours and 30 seconds and the next one 24 hours and 34 seconds. Is that even possible? Can the equation of time change that fast?  
> **username_4**: Yes! According to [this graph](https://en.wikipedia.org/wiki/File:Tijdvereffening-equation_of_time-en.jpg), it changes by about 17 seconds per day in December.  
> **username_4**: Does the sign of the change fit the claim?  
> **username_5**: Wouldn't altitude relative to the surrounding landscape have a significant effect?  If you live in a deep valley between high mountains, your "day" is going to be considerably shorter than if you lived on top of one of those mountains.  If you have high mountains to the east and open ocean to the west (as much of Oregon does), this would significantly offset your sunrise and sunset times.  
> **username_6**: -1. The discrepancy is not due to the equation of time. The length of daylight is a function of the Sun's declination. Since the Sun's declination is minimum at the winter solstice, the length of day is minimum at the solstice. The equation of time explains why the earliest sunset (Dec 7) and latest sunrise (Jan 4) occur on different dates and neither date is the solstice.  

---

