<p>Due to <a href="https://en.wikipedia.org/wiki/Axial_precession" rel="nofollow noreferrer">Axial precession</a> the Earth's axis changes direction with a period of 26,000 years as in the diagram:</p>

<p><a href="https://i.sstatic.net/kgaIU.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/kgaIU.png" alt="enter image description here"></a></p>

<p>If our calendar was defined by the position of Earth in it's orbit relative to the "fixed" stars, the North Pole will be tilted away from the sun in July 11,000 years hence.
However, according to <a href="http://curious.astro.cornell.edu/about-us/160-our-solar-system/the-earth/seasons/74-will-the-seasons-change-due-to-precession-intermediate" rel="nofollow noreferrer">Will the seasons change due to precession? </a></p>

<blockquote>
  <p>months are defined by seasons and so <strong>winter in the Northern hemisphere will never occur during June</strong>. At any point in future, the Northern hemisphere will experience summer during June and winter during December, but due to precesion, the months will correspond to different positions of the Earth's orbit around the Sun.</p>
</blockquote>

CC BY-SA 3.0
2018-04-21T11:13:35.280Z
I think you need to be more emphatic that the quote in OP is completely wrong.
Spencer
CC BY-SA 3.0
2018-04-21T16:10:09.127Z
@Spencer It hinges on our calendar being defined so that the solstices occur on the same dates, but I couldn't find a clear statement of that. It's not really an earth science question, or even astronomy.
Keith McClary
CC BY-SA 3.0
2018-04-21T16:11:30.150Z
The quote in OP referred to "winter solstice", not "winter", I find it hard to work out what that really means. Perhaps they were thinking of a position along the orbit? But I agree it is misleading or doesn't make much sense.
uUnwY
CC BY-SA 3.0
2018-04-21T22:51:19.297Z
@KeithMcClary  It would be helpful if you said where the question belongs instead of where it does not.
Centaurus
CC BY-SA 3.0
2018-04-22T00:41:19.950Z
@Centaurus I found this related Question in astronomy [Is there evidence for precession of the seasons?](https://astronomy.stackexchange.com/questions/21638/is-there-evidence-for-precession-of-the-seasons) with answer discussing the calendar aspect.
Keith McClary
CC BY-SA 3.0
2018-04-22T00:54:09.997Z
To understand these phenomena it is not necessary or useful to bring in calendar months. Just work in terms of the position of the solstices on Earth's orbit.
Keith McClary
CC BY-SA 3.0
2018-04-22T01:03:20.377Z
@KeithMcClary  I'm an amateur and it all sounds complicated to me. That's why I asked for a didatical explanation.  "If you're not using a calendar, the seasons are delayed but if you are using the Gregorian Calendar there is no change"   A simple sentence like this is beyond my ability to understand.  It seems I lack the basic knowledge on the subject. I have no idea what is meant by "a tropical year" and "a sidereal year". BTW, I'm just a cardiologist. lol.
Centaurus
CC BY-SA 3.0
2018-04-22T02:12:04.530Z
@Centaurus Yes, I got confused myself thinking about calendars, but they are an unnecessary complication. You don't need to know about tropical or sidereal either. There is a [Wikipedia article](https://en.wikipedia.org/wiki/Milankovitch_cycles).
Keith McClary
CC BY-SA 3.0
2018-04-22T06:42:48.393Z
@KeithMcClary The question specifically mentions July.  While the quote in the question is in error, I think its OK to bring months into the answer, even if it makes it somewhat longer.
userLTK
CC BY-SA 3.0
2018-04-21T02:58:27.010Z
2018-04-21T16:10:54.043Z
2018-04-21T16:10:54.043Z
Keith McClary
<blockquote>
  <p>Can anyone explain more didatically how such a shift is expected to
  happen? How the wobble movement is doing it?</p>
</blockquote>

<p>First, it's probably a bad approach to think of it as a shift.  It's a rotation.  similar to a spinning top.   <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/top.html" rel="noreferrer">It's called precession.</a>  It's always been there - (so to speak).  It's part of Earth's motion.</p>

<p>The Earth is sufficiently massive and space, sufficiently empty that there's effectively zero resistance and the Earth's precession is permanent and largely consistent.  (unlike a top that slows down due to friction from the ground and air resistance).  </p>

<p>Earth's precession shifts a tiny bit due to the sun, moon and gravity from other planets but those adjustments are very slow and not relevant to your question.</p>

<p>As Earth's precession completes one rotation every 22,000 years (give or take), over a human lifetime that's about 1.5 degrees or 1.5 days, which is pretty small and easily missed by anyone not taking very careful measurements. That doesn't affect calendars however.</p>

<p>Calendars are a little complicated, and I'm not sure it's necessary to go into that in detail for your question.   Calendars also can be adjusted to match Earth's orbit.   Any un-adjusted calendar will eventually mess things up like putting July in winter, but that has nothing to do with the 22,000 year precession.   365.25 days (a leap year every 4 years), was inaccurate enough to lead to <a href="https://www.historic-uk.com/HistoryUK/HistoryofBritain/Give-us-our-eleven-days/" rel="noreferrer">the year that lost 11 days</a> in the UK in 1752.</p>

<p>365.25 days (Julian calendar) is much more accurate than 365 days (which loses a day every 4 years (in effect, a 365 day year would put July in winter in 720 years, not 11,000).  Any movement of winter across the calendar depends on how good the calendar is, <strong>NOT</strong> earth's precession.  </p>

<p>365.242 days (<a href="https://en.wikipedia.org/wiki/Gregorian_calendar" rel="noreferrer">Gregorian calendar</a>), or 97 leap years every 400 years is better than the Julian (1 every 4).  Having an accurate accounting of leap years and being able to add or remove one as needed, will keep winter in the winter months for as long as we need to, much longer than 11,000 years.  </p>

<p>What changes with Earths precession is the position of the stars.  The sky will shift depending on where Earth is in it's 22,000 year wobble.  Similarly, the North star won't always be the North star.   The night sky will look shifted by about 46 degrees in 11,000 years (some of the stars will have moved over that time-frame as well, but lets ignore that for now).  </p>

<p>You've herd the term "Age of Aquarius".   <a href="https://en.wikipedia.org/wiki/Astrological_age" rel="noreferrer">The astrological ages</a> each last about 1,800-2,000 years, and the cycle of 12 ages corresponds to Earth's 22,000 year wobble.  Note, that article says 25,860 years and your quoted 22,000 years.  The solar system also wobbles, so how those wobbles add up can give different estimates.   If you use 22,000 or 25,860 or 25,771 or 26,000 or 23,000 on average, the different numbers don't change the answer to this question.   <a href="https://en.wikipedia.org/wiki/Milankovitch_cycles#Apsidal_precession" rel="noreferrer">This explains the variation in the numbers used</a>.  </p>

<blockquote>
  <p>Is such an astronomic phenomenon accepted by scientists
  unquestionably?</p>
</blockquote>

<p>Absolutely, 100%, unquestionably yes.  This is accepted, measured, confirmed and can be modeled and explained.  It's 100% accepted science.  Even <a href="http://www.crystalinks.com/precession.html" rel="noreferrer">the ancients were able to observe this</a> with careful measurement, though they couldn't accurately explain it.</p>

<blockquote>
  <p>If winter is expected to be in July 11,000 years from now and such a
  shift is under way right now, does it mean that winter in the NH is
  slowly moving towards July and that, perhaps, 5,000 years from now
  winter solstice will be in March</p>
</blockquote>

<p>As the assumption is flawed, then both no and yes.  With an imperfect calendar, then this would happen and the rate would depend on the accuracy of the calendar as noted above (not precession).  </p>

<p>Because we use a very accurate calendar that allows for adding and removing a leap year as needed, no "drifting" of the solstices across the months will happen.   There will be some yearly variation as the solstice is a precise point in Earth's orbit, so it happens not only on a day but at a precise time, it might be December 21 one year and December 22 the next year, but every year our calendar gets "messed up" by about 6 hours, and every 4 years, that 6 hour error is mostly corrected.   Jupiter also accelerates or decelerates the Earth in it's orbit and Earth's orbital speed varies depending on how close to perihelion and aphelion, so there's some variation year to year, but there's no movement across the calendar over 11,000 years.</p>

CC BY-SA 3.0
2018-04-22T12:00:12.543Z
Great answer. You sure know your subject. I gather the person who wrote that NGM paragraph is not a scientist. Or maybe they wanted to be sensationalistic by saying that winter will be in July.  Thank you.
Centaurus
CC BY-SA 3.0
2018-04-22T08:48:39.690Z
2018-04-22T08:48:39.690Z
userLTK
<p>The July 2007 issue of the National Geographic Magazine dedicates several pages to <strong>"Climate Change"</strong> and <strong>"Global Warming"</strong>.  The author explains in detail the Earth's movements and how they provoke great climate shifts.  <strong>"Wobble"</strong> is one of the four movements listed and is described as follows:</p>

<blockquote>
  <ul>
  <li>"Earth slowly wobbles like a top as it spins on its axis, which shifts back and forth about every 20,000 years. The result: <strong>About 11,000 years from now, winter solstice in the Northern Hemisphere will be in July.</strong></li>
  </ul>
</blockquote>

<p>Although I know exactly what a top is, and how it spins, I find it hard to understand how wobbling is expected to bring about that forecast.</p>

<ol>
<li>Can anyone explain more didatically how such a shift is expected to happen? How the wobble movement is doing it?</li>
<li>Is such an astronomic phenomenon accepted by scientists unquestionably?</li>
<li>If winter is expected to be in July 11,000 years from now and such a shift is under way right now, does it mean that winter in the NH is slowly moving towards July and that, perhaps, 5,000 years from now winter solstice will be in March? </li>
</ol>

<p>Thank you.</p>

CC BY-SA 4.0
2018-07-05T09:33:55.127Z
TLK's answer is top notch. Wonder if it might be tough for some still... one thing that may help that I didn't understand when younger is a year looks like [this](https://upload.wikimedia.org/wikipedia/commons/5/58/Earth_tilt_animation.gif), not an oscillating tilt. And that alone accounts for the seasons. So precession is just a *very* gradual change of that tilt (NP about the circle in Keith's answer), indeed like a top. It changes star position, but it's continual, so accurate calendars account for it. Hope that helps pull it together for some people, but if not, don't be afraid to ask.
JeopardyTempest
CC BY-SA 3.0
2018-04-21T03:00:10.300Z
I think this should be in astronomy.SE .
Keith McClary
CC BY-SA 3.0
2018-04-21T03:07:16.987Z
Not any expertise from me, but perhaps it's important keep in mind that unlike a top, there's no blocking point (where the body of the top prevents further tipping) (and the force isn't down, but instead inward towards the sun)
JeopardyTempest
CC BY-SA 3.0
2018-04-21T19:31:25.797Z
I wonder if the author (Nat Geo, not you) understands the difference between a sidereal year and a tropical year?
BillDOe
CC BY-SA 3.0
2018-04-24T23:21:11.030Z
I think this is on-topic here. It might overlap with [astronomy.se], but I think since the question focuses on Earth's movements and not all/any planet's movements, it is in scope.
hichris123
<geophysics><climate-change><climate-models>
Winter in the Northern Hemisphere in July? Can anyone explain it?
Centaurus
# Winter in the Northern Hemisphere in July? Can anyone explain it?

(Asked by: username_0 on 2018-04-20)

The July 2007 issue of the National Geographic Magazine dedicates several pages to **"Climate Change"** and **"Global Warming"**. The author explains in detail the Earth's movements and how they provoke great climate shifts. **"Wobble"** is one of the four movements listed and is described as follows:

> * "Earth slowly wobbles like a top as it spins on its axis, which shifts back and forth about every 20,000 years. The result: **About 11,000 years from now, winter solstice in the Northern Hemisphere will be in July.**

Although I know exactly what a top is, and how it spins, I find it hard to understand how wobbling is expected to bring about that forecast.

1. Can anyone explain more didatically how such a shift is expected to happen? How the wobble movement is doing it?
2. Is such an astronomic phenomenon accepted by scientists unquestionably?
3. If winter is expected to be in July 11,000 years from now and such a shift is under way right now, does it mean that winter in the NH is slowly moving towards July and that, perhaps, 5,000 years from now winter solstice will be in March?

Thank you.

**Tags:** geophysics, climate-change, climate-models

> **Comments:**
> **username_2**: I think this should be in astronomy.SE .  
> **username_1**: Not any expertise from me, but perhaps it's important keep in mind that unlike a top, there's no blocking point (where the body of the top prevents further tipping) (and the force isn't down, but instead inward towards the sun)  
> **username_3**: I wonder if the author (Nat Geo, not you) understands the difference between a sidereal year and a tropical year?  
> **username_4**: I think this is on-topic here. It might overlap with [astronomy.se], but I think since the question focuses on Earth's movements and not all/any planet's movements, it is in scope.  
> **username_1**: TLK's answer is top notch. Wonder if it might be tough for some still... one thing that may help that I didn't understand when younger is a year looks like [this](https://upload.wikimedia.org/wikipedia/commons/5/58/Earth_tilt_animation.gif), not an oscillating tilt. And that alone accounts for the seasons. So precession is just a *very* gradual change of that tilt (NP about the circle in username_2's answer), indeed like a top. It changes star position, but it's continual, so accurate calendars account for it. Hope that helps pull it together for some people, but if not, don't be afraid to ask.  

---

## 2 answers

### Answer by username_7 on 2018-04-22. Score: 5 | Accepted answer

> Can anyone explain more didatically how such a shift is expected to
> happen? How the wobble movement is doing it?

First, it's probably a bad approach to think of it as a shift. It's a rotation. similar to a spinning top. [It's called precession.](http://hyperphysics.phy-astr.gsu.edu/hbase/top.html) It's always been there - (so to speak). It's part of Earth's motion.

The Earth is sufficiently massive and space, sufficiently empty that there's effectively zero resistance and the Earth's precession is permanent and largely consistent. (unlike a top that slows down due to friction from the ground and air resistance).

Earth's precession shifts a tiny bit due to the sun, moon and gravity from other planets but those adjustments are very slow and not relevant to your question.

As Earth's precession completes one rotation every 22,000 years (give or take), over a human lifetime that's about 1.5 degrees or 1.5 days, which is pretty small and easily missed by anyone not taking very careful measurements. That doesn't affect calendars however.

Calendars are a little complicated, and I'm not sure it's necessary to go into that in detail for your question. Calendars also can be adjusted to match Earth's orbit. Any un-adjusted calendar will eventually mess things up like putting July in winter, but that has nothing to do with the 22,000 year precession. 365.25 days (a leap year every 4 years), was inaccurate enough to lead to [the year that lost 11 days](https://www.historic-uk.com/HistoryUK/HistoryofBritain/Give-us-our-eleven-days/) in the UK in 1752.

365.25 days (Julian calendar) is much more accurate than 365 days (which loses a day every 4 years (in effect, a 365 day year would put July in winter in 720 years, not 11,000). Any movement of winter across the calendar depends on how good the calendar is, **NOT** earth's precession.

365.242 days ([Gregorian calendar](https://en.wikipedia.org/wiki/Gregorian_calendar)), or 97 leap years every 400 years is better than the Julian (1 every 4). Having an accurate accounting of leap years and being able to add or remove one as needed, will keep winter in the winter months for as long as we need to, much longer than 11,000 years.

What changes with Earths precession is the position of the stars. The sky will shift depending on where Earth is in it's 22,000 year wobble. Similarly, the North star won't always be the North star. The night sky will look shifted by about 46 degrees in 11,000 years (some of the stars will have moved over that time-frame as well, but lets ignore that for now).

You've herd the term "Age of Aquarius". [The astrological ages](https://en.wikipedia.org/wiki/Astrological_age) each last about 1,800-2,000 years, and the cycle of 12 ages corresponds to Earth's 22,000 year wobble. Note, that article says 25,860 years and your quoted 22,000 years. The solar system also wobbles, so how those wobbles add up can give different estimates. If you use 22,000 or 25,860 or 25,771 or 26,000 or 23,000 on average, the different numbers don't change the answer to this question. [This explains the variation in the numbers used](https://en.wikipedia.org/wiki/Milankovitch_cycles#Apsidal_precession).

> Is such an astronomic phenomenon accepted by scientists
> unquestionably?

Absolutely, 100%, unquestionably yes. This is accepted, measured, confirmed and can be modeled and explained. It's 100% accepted science. Even [the ancients were able to observe this](http://www.crystalinks.com/precession.html) with careful measurement, though they couldn't accurately explain it.

> If winter is expected to be in July 11,000 years from now and such a
> shift is under way right now, does it mean that winter in the NH is
> slowly moving towards July and that, perhaps, 5,000 years from now
> winter solstice will be in March

As the assumption is flawed, then both no and yes. With an imperfect calendar, then this would happen and the rate would depend on the accuracy of the calendar as noted above (not precession).

Because we use a very accurate calendar that allows for adding and removing a leap year as needed, no "drifting" of the solstices across the months will happen. There will be some yearly variation as the solstice is a precise point in Earth's orbit, so it happens not only on a day but at a precise time, it might be December 21 one year and December 22 the next year, but every year our calendar gets "messed up" by about 6 hours, and every 4 years, that 6 hour error is mostly corrected. Jupiter also accelerates or decelerates the Earth in it's orbit and Earth's orbital speed varies depending on how close to perihelion and aphelion, so there's some variation year to year, but there's no movement across the calendar over 11,000 years.

> **Comments:**
> **username_0**: Great answer. You sure know your subject. I gather the person who wrote that NGM paragraph is not a scientist. Or maybe they wanted to be sensationalistic by saying that winter will be in July.  Thank you.  

---

### Answer by username_2 on 2018-04-21. Score: 2

Due to [Axial precession](https://en.wikipedia.org/wiki/Axial_precession) the Earth's axis changes direction with a period of 26,000 years as in the diagram:

[![enter image description here](https://i.sstatic.net/kgaIU.png)](https://i.sstatic.net/kgaIU.png)

If our calendar was defined by the position of Earth in it's orbit relative to the "fixed" stars, the North Pole will be tilted away from the sun in July 11,000 years hence.
However, according to [Will the seasons change due to precession?](http://curious.astro.cornell.edu/about-us/160-our-solar-system/the-earth/seasons/74-will-the-seasons-change-due-to-precession-intermediate)

> months are defined by seasons and so **winter in the Northern hemisphere will never occur during June**. At any point in future, the Northern hemisphere will experience summer during June and winter during December, but due to precesion, the months will correspond to different positions of the Earth's orbit around the Sun.

> **Comments:**
> **username_5**: I think you need to be more emphatic that the quote in OP is completely wrong.  
> **username_2**: @username_5 It hinges on our calendar being defined so that the solstices occur on the same dates, but I couldn't find a clear statement of that. It's not really an earth science question, or even astronomy.  
> **username_6**: The quote in OP referred to "winter solstice", not "winter", I find it hard to work out what that really means. Perhaps they were thinking of a position along the orbit? But I agree it is misleading or doesn't make much sense.  
> **username_0**: @username_2  It would be helpful if you said where the question belongs instead of where it does not.  
> **username_2**: @username_0 I found this related Question in astronomy [Is there evidence for precession of the seasons?](https://astronomy.stackexchange.com/questions/21638/is-there-evidence-for-precession-of-the-seasons) with answer discussing the calendar aspect.  
> **username_2**: To understand these phenomena it is not necessary or useful to bring in calendar months. Just work in terms of the position of the solstices on Earth's orbit.  
> **username_0**: @username_2  I'm an amateur and it all sounds complicated to me. That's why I asked for a didatical explanation.  "If you're not using a calendar, the seasons are delayed but if you are using the Gregorian Calendar there is no change"   A simple sentence like this is beyond my ability to understand.  It seems I lack the basic knowledge on the subject. I have no idea what is meant by "a tropical year" and "a sidereal year". BTW, I'm just a cardiologist. lol.  
> **username_2**: @username_0 Yes, I got confused myself thinking about calendars, but they are an unnecessary complication. You don't need to know about tropical or sidereal either. There is a [Wikipedia article](https://en.wikipedia.org/wiki/Milankovitch_cycles).  
> **username_7**: @username_2 The question specifically mentions July.  While the quote in the question is in error, I think its OK to bring months into the answer, even if it makes it somewhat longer.  

---

