<p>We have &quot;days&quot; because the Earth is rotating. The shape of the orbit has little effect on the daily cycle of light and dark.</p>
<p>The varying length of the day is determined by the tilt of Earth relative to the plane of the orbit of the Earth around the sun.  When the Northern hemisphere is pointed away from the sun, then the sun is low in the sky and is below the horizon for longer. So the shortest day happens when the Earth is at the point in its orbit when the angle that the Earth's axis makes with the line from the Earth to the Sun is greatest. This is on about the 21 December.</p>
<p>The longest and shortest days of the year occur because of the tilt of the planet, which also controls when the Equinoxes and Solstices occur. The tilt of the planet has absolutely nothing to do with its location in orbit, and it's only pure coincidence that they're so close together. Also, perihelion moves over time (apsidal precession) and in 56,000 years it would occur on the longest day in the Northern Hemisphere. Except for the fact that the Earth's axis will have also precessed (with a period of around 26,000 years) so the shortest day will occur somewhere else on in the Earth's orbit</p>
<p>For the sake of clarity: The equinox does not occur on the minor axis. The solstice does not occur on the major axis. The tilt of the Earth to then orbital plane does not change over the course of the year, and the Earth's rotational axis is no aligned with the major axis of the Earth's orbit.</p>

CC BY-SA 4.0
2020-01-12T16:56:47.347Z
+1  Indeed.  Also, perihelion moves over time (apsidal precession) and in 56,000 years it would occur on the longest day in the Northern Hemisphere.  Except for the fact that the Earth's axis will have also precessed (with a period of around 26,000 years) so the shortest day will occur somewhere else on in the Earth's orbit
Dave Gremlin
CC BY-SA 4.0
2020-01-12T23:18:22.190Z
Let me put up the question differently. Its really not Northern or Southern hemisphere. The question is Should the Equinox and Solstice occur at Minor axis and Major axis since the orbit is Elliptical?
Mohan Mone
CC BY-SA 4.0
2020-01-12T23:55:09.413Z
@MohanMone The answer remains exactly the same. The longest and shortest days of the year occur because of the tilt of the planet, which also controls when the Equinoxes and Solstices occur. The tilt of the planet has absolutely nothing to do with its location in orbit, and it's only pure coincidence that they're so close together.
HiddenWindshield
CC BY-SA 4.0
2020-01-13T01:16:09.087Z
At equinox there is equal day and night. This means the tilt towards sun is ZERO, hence the point should be on Minor axis otherwise any other point on elliptical orbit either North or South pole will be towards the sun-may be extremely small angle-and hence day and night can not be exactly equal. Hence my question- if the equinox is on minor axis then solstice should be on major axis
Mohan Mone
CC BY-SA 4.0
2020-01-13T05:27:19.133Z
@MohanMone The piece you are missing is the tilt of the earth is not parallel to the major axis of the elliptical orbit, so the equinoxes/solstices are not lined up with the major/minor axes.  There is no "the tilt towards sun is ZERO, hence the point should be on the Minor axis" because there's no reason for it to be.
throx
CC BY-SA 4.0
2020-01-13T13:20:15.177Z
I feel that this could be easily demonstrated by a nice 3D animation (that exaggerates the eccentricity of the orbit), but it seems like quite a lot of work for just a SE answer. But perhaps such an animation already exists?
JiK
CC BY-SA 4.0
2020-01-13T15:33:51.707Z
It is worth adding that this coincidence is only valid for the current timeframe. The Earth axis changes because of the precession movement but with a period of 26k years. http://hosting.astro.cornell.edu/academics/courses/astro201/earth_precess.htm but @DaveGremlin just did. OOps.
Mindwin Remember Monica
CC BY-SA 4.0
2020-01-12T08:45:41.190Z
2023-02-06T04:47:57.717Z
2023-02-06T04:47:57.717Z
James K
<p>Equinoxes and solstices are determined by the direction of tilt of the planet's daily rotation. The direction of tilt of a planet's rotational axis is essentially random, (mostly) constant, and unrelated to any property of its orbit.</p>

<p>I did not calculate the precise correct position of the sun in the below diagram, but it doesn't need to be precise to illustrate the point. The planet's tilt is toward the upper right of the diagram at all points in the orbit, changing only very slowly in a process called precession that takes many millennia.</p>

<p><a href="https://i.sstatic.net/s58Gc.png" rel="noreferrer"><img src="https://i.sstatic.net/s58Gc.png" alt="Diagram of equinoxes and solstices on an orbit"></a></p>

CC BY-SA 4.0
2020-01-13T14:23:51.123Z
Nice diagram. Just to make it clear that there's no preferred direction or no preferred hemisphere, "Tilt" could have arrows in both directions and "Summer Solstice" and "Winter Solstice" could just be "Solstice"s.
Eric Duminil
CC BY-SA 4.0
2020-01-13T05:38:53.303Z
2020-01-13T05:44:40.003Z
2020-01-13T05:44:40.003Z
Douglas
<p>The amount of daylight does not define a day. A day is defined as between noon one day until noon the following day.
Because the earth is closer to the Sun during the Perihelion, it moves faster through the orbit. This means that it travels farther between noon Jan 4 and Jan 5 than between July 4 and July 5. Because the earth moves farther, it must rotate more before it is noon the following day. That makes January 4 a few seconds longer than July 4.</p>

CC BY-SA 4.0
2023-12-21T17:52:06.967Z
Your answer is technically correct, but the original question is using "length of day" to mean the length of daylight: the time from sunrise until sunset. That occurs on the winter solstice (Dec 21 for Norther hemisphere), not at perihelion.
JohnHoltz
CC BY-SA 4.0
2023-12-22T19:24:58.160Z
The length of a day remains at approximately 24 hours all year long and the length of a day is the same in the northern and southern hemisphere. The words "day" and "daylight" are the cause of the confusion.
Mark Daniel
CC BY-SA 4.0
2023-12-26T10:14:10.700Z
Unfortunately, "day" is ambiguous in English.  It can mean "a period of 24 hours" but it can also mean "the period from sunrise to sunset".  You just have to guess from the context.  Some languages have separate terms.
badjohn
CC BY-SA 4.0
2023-12-26T11:31:40.660Z
The solar day length varies from 24 hours - ~22 seconds to 24 hours + ~30 seconds. See my answer https://physics.stackexchange.com/a/790695/123208
PM 2Ring
CC BY-SA 4.0
2023-12-21T15:29:24.070Z
2023-12-21T15:29:24.070Z
Mark Daniel
<p>The orbit of Earth is elliptical and the nearest distance to sun is perihelion position. Should it not be the shortest day in the northern hemisphere?</p>

CC BY-SA 4.0
2020-01-12T16:46:12.793Z
Why should it be any different if you apply the exact same logic to the Southern Hemisphere? North and South aren't related to perihelion/aphelion.
Eric Duminil
CC BY-SA 4.0
2020-01-12T19:09:49.363Z
The real question you should be asking is why perihelion and the northern winter solstice are so _close together_, only a couple of weeks apart. And the answer is that it’s just a coincidence.
Mike Scott
CC BY-SA 4.0
2020-01-14T06:26:36.413Z
Clearly, the Illuminati got their math wrong when they were coming up with the Globe Earth story.
Acccumulation
CC BY-SA 4.0
2020-01-14T15:03:08.017Z
The shortest day (in the northern hemisphere) occurs when Earth's axis of rotation is tilted furthest away from the sun.

Perihelion occurs when the orbit of Earth takes it nearest to the sun.

The events arise from unrelated causes and are therefore also unrelated.
Vince O'Sullivan
CC BY-SA 4.0
2020-01-17T16:49:27.117Z
I asked a very similar question 6 months ago: https://astronomy.stackexchange.com/questions/32470/aphelion-and-the-solstice
badjohn
<earth>
Why are perihelion and the shortest day in the northern hemisphere different?
Mohan Mone
# Why are perihelion and the shortest day in the northern hemisphere different?

(Asked by: username_0 on 2020-01-12)

The orbit of Earth is elliptical and the nearest distance to sun is perihelion position. Should it not be the shortest day in the northern hemisphere?

**Tags:** earth

> **Comments:**
> **username_1**: Why should it be any different if you apply the exact same logic to the Southern Hemisphere? North and South aren't related to perihelion/aphelion.  
> **username_2**: The real question you should be asking is why perihelion and the northern winter solstice are so _close together_, only a couple of weeks apart. And the answer is that it’s just a coincidence.  
> **username_3**: Clearly, the Illuminati got their math wrong when they were coming up with the Globe Earth story.  
> **username_4**: The shortest day (in the northern hemisphere) occurs when Earth's axis of rotation is tilted furthest away from the sun.  Perihelion occurs when the orbit of Earth takes it nearest to the sun.  The events arise from unrelated causes and are therefore also unrelated.  
> **username_5**: I asked a very similar question 6 months ago: https://astronomy.stackexchange.com/questions/32470/aphelion-and-the-solstice  

---

## 3 answers

### Answer by username_6 on 2020-01-12. Score: 32

We have "days" because the Earth is rotating. The shape of the orbit has little effect on the daily cycle of light and dark.

The varying length of the day is determined by the tilt of Earth relative to the plane of the orbit of the Earth around the sun. When the Northern hemisphere is pointed away from the sun, then the sun is low in the sky and is below the horizon for longer. So the shortest day happens when the Earth is at the point in its orbit when the angle that the Earth's axis makes with the line from the Earth to the Sun is greatest. This is on about the 21 December.

The longest and shortest days of the year occur because of the tilt of the planet, which also controls when the Equinoxes and Solstices occur. The tilt of the planet has absolutely nothing to do with its location in orbit, and it's only pure coincidence that they're so close together. Also, perihelion moves over time (apsidal precession) and in 56,000 years it would occur on the longest day in the Northern Hemisphere. Except for the fact that the Earth's axis will have also precessed (with a period of around 26,000 years) so the shortest day will occur somewhere else on in the Earth's orbit

For the sake of clarity: The equinox does not occur on the minor axis. The solstice does not occur on the major axis. The tilt of the Earth to then orbital plane does not change over the course of the year, and the Earth's rotational axis is no aligned with the major axis of the Earth's orbit.

> **Comments:**
> **username_7**: +1  Indeed.  Also, perihelion moves over time (apsidal precession) and in 56,000 years it would occur on the longest day in the Northern Hemisphere.  Except for the fact that the Earth's axis will have also precessed (with a period of around 26,000 years) so the shortest day will occur somewhere else on in the Earth's orbit  
> **username_0**: Let me put up the question differently. Its really not Northern or Southern hemisphere. The question is Should the Equinox and Solstice occur at Minor axis and Major axis since the orbit is Elliptical?  
> **username_8**: @MohanMone The answer remains exactly the same. The longest and shortest days of the year occur because of the tilt of the planet, which also controls when the Equinoxes and Solstices occur. The tilt of the planet has absolutely nothing to do with its location in orbit, and it's only pure coincidence that they're so close together.  
> **username_0**: At equinox there is equal day and night. This means the tilt towards sun is ZERO, hence the point should be on Minor axis otherwise any other point on elliptical orbit either North or South pole will be towards the sun-may be extremely small angle-and hence day and night can not be exactly equal. Hence my question- if the equinox is on minor axis then solstice should be on major axis  
> **username_9**: @MohanMone The piece you are missing is the tilt of the earth is not parallel to the major axis of the elliptical orbit, so the equinoxes/solstices are not lined up with the major/minor axes.  There is no "the tilt towards sun is ZERO, hence the point should be on the Minor axis" because there's no reason for it to be.  
> **username_10**: I feel that this could be easily demonstrated by a nice 3D animation (that exaggerates the eccentricity of the orbit), but it seems like quite a lot of work for just a SE answer. But perhaps such an animation already exists?  
> **username_11**: It is worth adding that this coincidence is only valid for the current timeframe. The Earth axis changes because of the precession movement but with a period of 26k years. http://hosting.astro.cornell.edu/academics/courses/astro201/earth_precess.htm but @DaveGremlin just did. OOps.  

---

### Answer by username_12 on 2020-01-13. Score: 15

Equinoxes and solstices are determined by the direction of tilt of the planet's daily rotation. The direction of tilt of a planet's rotational axis is essentially random, (mostly) constant, and unrelated to any property of its orbit.

I did not calculate the precise correct position of the sun in the below diagram, but it doesn't need to be precise to illustrate the point. The planet's tilt is toward the upper right of the diagram at all points in the orbit, changing only very slowly in a process called precession that takes many millennia.

[![Diagram of equinoxes and solstices on an orbit](https://i.sstatic.net/s58Gc.png)](https://i.sstatic.net/s58Gc.png)

> **Comments:**
> **username_1**: Nice diagram. Just to make it clear that there's no preferred direction or no preferred hemisphere, "Tilt" could have arrows in both directions and "Summer Solstice" and "Winter Solstice" could just be "Solstice"s.  

---

### Answer by username_13 on 2023-12-21. Score: -1

The amount of daylight does not define a day. A day is defined as between noon one day until noon the following day.
Because the earth is closer to the Sun during the Perihelion, it moves faster through the orbit. This means that it travels farther between noon Jan 4 and Jan 5 than between July 4 and July 5. Because the earth moves farther, it must rotate more before it is noon the following day. That makes January 4 a few seconds longer than July 4.

> **Comments:**
> **username_14**: Your answer is technically correct, but the original question is using "length of day" to mean the length of daylight: the time from sunrise until sunset. That occurs on the winter solstice (Dec 21 for Norther hemisphere), not at perihelion.  
> **username_13**: The length of a day remains at approximately 24 hours all year long and the length of a day is the same in the northern and southern hemisphere. The words "day" and "daylight" are the cause of the confusion.  
> **username_5**: Unfortunately, "day" is ambiguous in English.  It can mean "a period of 24 hours" but it can also mean "the period from sunrise to sunset".  You just have to guess from the context.  Some languages have separate terms.  
> **username_15**: The solar day length varies from 24 hours - ~22 seconds to 24 hours + ~30 seconds. See my answer https://physics.stackexchange.com/a/790695/123208  

---

