# Is the earth slowing down at all? **URL:** \ **Category:** Factual Questions\ **Created:** [August 1, 2005, 11:13pm UTC](https://boards.straightdope.com/t/is-the-earth-slowing-down-at-all/315221 "2005-08-01T23:13:09Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![Can\_Handle\_the\_Truth](https://avatars.discourse-cdn.com/v4/letter/c/6a8cbe/32.png) [@Can\_Handle\_the\_Truth](https://boards.straightdope.com/u/Can_Handle_the_Truth)\ **Post date:** [August 1, 2005, 11:13pm UTC](https://boards.straightdope.com/t/is-the-earth-slowing-down-at-all/315221/1 "2005-08-01T23:13:09Z")
I was wondering if there is any measurable slowing of the speed of the earth in its orbit around the sun. ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [August 2, 2005, 12:46am UTC](https://boards.straightdope.com/t/is-the-earth-slowing-down-at-all/315221/2 "2005-08-02T00:46:46Z")
It speeds up and slows as it is closer and farther from the Sun in its elliptical orbit. That causes a problem in that the Sun _appears_ to speed and slow in its daily trip through the sky, described by the _equation of time_. The Sun also moves North and South because of the Earth’s tilt, so a picture of the Sun taken at exactly 12 o’clock (standard time) would show a figure eight–called an analemma. ---
**Author:** ![spingears](https://avatars.discourse-cdn.com/v4/letter/s/ebca7d/32.png) [@spingears](https://boards.straightdope.com/u/spingears)\ **Post date:** [August 2, 2005, 1:36am UTC](https://boards.straightdope.com/t/is-the-earth-slowing-down-at-all/315221/3 "2005-08-02T01:36:04Z")
> [@RM Mentock](#): > > It speeds up and slows as it is closer and farther from the Sun in its elliptical orbit. That causes a problem in that the Sun _appears_ to speed and slow in its daily trip through the sky, described by the _equation of time_. The Sun also moves North and South because of the Earth’s tilt, so a picture of the Sun taken at exactly 12 o’clock (standard time) would show a figure eight–called an analemma. Didn’t you mean a series of daily pictures of the Sun taken at exactly 12 o’clock (standard time) would show a figure eight–called an analemma? ---
**Author:** ![Can\_Handle\_the\_Truth](https://avatars.discourse-cdn.com/v4/letter/c/6a8cbe/32.png) [@Can\_Handle\_the\_Truth](https://boards.straightdope.com/u/Can_Handle_the_Truth)\ **Post date:** [August 2, 2005, 1:51am UTC](https://boards.straightdope.com/t/is-the-earth-slowing-down-at-all/315221/4 "2005-08-02T01:51:09Z")
> [@RM Mentock](#): > > It speeds up and slows as it is closer and farther from the Sun in its elliptical orbit. Yeah, I know that. I want to know if its net speed is decreasing. ---
**Author:** ![Absolute](https://avatars.discourse-cdn.com/v4/letter/a/b2d939/32.png) [@Absolute](https://boards.straightdope.com/u/Absolute)\ **Post date:** [August 2, 2005, 2:08am UTC](https://boards.straightdope.com/t/is-the-earth-slowing-down-at-all/315221/5 "2005-08-02T02:08:07Z")
> [@Can Handle the Truth](#): > > Yeah, I know that. I want to know if its net speed is decreasing. I can’t answer this question, but the speed of the earth’s _rotation_ is decreasing. The moon creates a drag on the earth’s rotation, primarily because of all the loose water we have sitting around on the surface of the planet (and the tides the moon creates in this water). A great description may be found at the wikipedia article: [Tidal acceleration](http://en.wikipedia.org/wiki/Tidal_acceleration). Notably: > [@Wikipedia](#): > > The Earth’s day lengthens by about 15 µs every year. ---
**Author:** ![Bytegeist](https://avatars.discourse-cdn.com/v4/letter/b/9dc877/32.png) [@Bytegeist](https://boards.straightdope.com/u/Bytegeist)\ **Post date:** [August 2, 2005, 2:12am UTC](https://boards.straightdope.com/t/is-the-earth-slowing-down-at-all/315221/6 "2005-08-02T02:12:29Z")
> [@Can Handle the Truth](#): > > Yeah, I know that. I want to know if its net speed is decreasing. There are long (~ 10[sup]5[/sup] year) cyclic periods in the [orbit’s](http://www.ldeo.columbia.edu/users/jcm/Topic2/Topic2.html) [eccentricity](http://www.geolsoc.org.uk/template.cfm?name=Milankovitch), which result in a similar cyclic period in the mean orbital speed. I don’t know whether we are currently in an increasing or decreasing phase. In any case, the effect is pretty tiny from year to year. There are also small chaotic fluctuations in the earth’s orbit due to it being pulled this way and that way by the other planets, which are never in exactly the same arrangment twice. Over the long haul these tugs tend to cancel out — though there is no guarantee they will perfectly cancel out over the long run. Still, overall the earth’s orbit is pretty close to constant. You can’t really say that there’s a general slowing trend. (Well, you can say it if you want. _I’m_ not going to say it.) ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [August 2, 2005, 2:14am UTC](https://boards.straightdope.com/t/is-the-earth-slowing-down-at-all/315221/7 "2005-08-02T02:14:15Z")
It’s decreasing, although at such a small rate that it’s probably not measurable. The sun is slowly losing mass, mainly due to the solar wind, and thus it’s gravitational pull is getting weaker. As a result, the planets’ orbits are very slowly expanding and they will move slower in these larger orbits. However, as I said, I doubt this effect is measurable. At least I’ve never heard of anyone trying to measure it, which may not mean much since I’m not a professional astronomer. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [August 2, 2005, 3:55am UTC](https://boards.straightdope.com/t/is-the-earth-slowing-down-at-all/315221/8 "2005-08-02T03:55:55Z")
I recall reading in Stephen Hawking’s book A Brief History of Time that the earth loses energy in the form of gravitational waves (like a cork bobbing in water). This will cause the earth to eventually spiral into the sun. That said the energy loss is very small (IIRC Hawking said it would be enough to run a toaster) so the sun will have burnt out long before this occurs. What I always forget about this is that while the earth loses energy it will (I think) actually speed up as its orbit gets smaller. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [August 2, 2005, 4:02am UTC](https://boards.straightdope.com/t/is-the-earth-slowing-down-at-all/315221/9 "2005-08-02T04:02:03Z")
The quote below seems to indicate the earth is not slowing down. The question was asked if it slowed like satellites in earth orbit do due to friction from the atmosphere but one would think if there was another effect slowing the earth they would mention it. > [@](#): > > That doesn’t quite answer the question though- does Earth experience slowing of its orbit because of contact with the Sun’s ‘atmosphere’. The short answer is no- the sun is so far away and the Earth is so heavy that any force is very very small and any acceleration is far smaller! In fact, if the orbit started to decay, the radiation pressure of all of the light from the sun would increase, which would act to limit the rate of decay. So overall- probably not. > > SOURCE: [http://www.physlink.com/Education/AskExperts/ae499.cfm](http://www.physlink.com/Education/AskExperts/ae499.cfm) ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [August 2, 2005, 4:05am UTC](https://boards.straightdope.com/t/is-the-earth-slowing-down-at-all/315221/10 "2005-08-02T04:05:09Z")
[QUOTE=Can Handle the Truth] Well, the earth is always powing through the solar wind which has a velocity approximately at right angles to the earth’s velocity in its orbit. I would expect that would have some small effect. ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [August 2, 2005, 10:57am UTC](https://boards.straightdope.com/t/is-the-earth-slowing-down-at-all/315221/11 "2005-08-02T10:57:25Z")
> [@spingears](#): > > Didn’t you mean a series of daily pictures of the Sun taken at exactly 12 o’clock (standard time) would show a figure eight–called an analemma? yep, thanks ---
**Author:** ![Bryan\_Ekers](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bryan_ekers/32/183_2.png) [@Bryan\_Ekers](https://boards.straightdope.com/u/Bryan_Ekers)\ **Post date:** [August 2, 2005, 11:32am UTC](https://boards.straightdope.com/t/is-the-earth-slowing-down-at-all/315221/12 "2005-08-02T11:32:04Z")
Interestingly, a search of “atomic leap seconds” leads to pages documenting the efforts of various international agencies to keep their atomic clocks syncronized to so-called Universal Time. A nanosecond gets added now and then. ---
**Author:** ![Hombre](https://avatars.discourse-cdn.com/v4/letter/h/ecb155/32.png) [@Hombre](https://boards.straightdope.com/u/Hombre)\ **Post date:** [August 2, 2005, 1:14pm UTC](https://boards.straightdope.com/t/is-the-earth-slowing-down-at-all/315221/13 "2005-08-02T13:14:02Z")
Quote, “…the sun is so far away and the Earth is so heavy that any force is very very small…” IINAA, but this seems dubious. The sun is the _reason_ for earths orbit. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [August 2, 2005, 1:52pm UTC](https://boards.straightdope.com/t/is-the-earth-slowing-down-at-all/315221/14 "2005-08-02T13:52:33Z")
> [@Hombre](#): > > Quote, “…the sun is so far away and the Earth is so heavy that any force is very very small…” > > IINAA, but this seems dubious. The sun is the _reason_ for earths orbit. Did you read the link? They are talking about the effect of the sun’s _atmosphere_. Because the sun is far away, and because Earth is relatively large, the effect of the sun’s atmosphere is negligible. This differs from the case of artificial satellites orbiting the Earth, which eventually have their orbits decay because they are close enough and light enough to be affected and slowed by friction with Earth’s atmosphere.