# Is the earth's orbit slowing down? **URL:** \ **Category:** Factual Questions\ **Created:** [January 2, 2004, 3:32pm UTC](https://boards.straightdope.com/t/is-the-earths-orbit-slowing-down/222294 "2004-01-02T15:32:17Z")\ **Posts on this page:** 18\ **Page:** 1
**Author:** ![Gold\_Dragon](https://avatars.discourse-cdn.com/v4/letter/g/d9b06d/32.png) [@Gold\_Dragon](https://boards.straightdope.com/u/Gold_Dragon)\ **Post date:** [January 2, 2004, 3:32pm UTC](https://boards.straightdope.com/t/is-the-earths-orbit-slowing-down/222294/1 "2004-01-02T15:32:17Z")
[CNN article](http://www.cnn.com/2004/TECH/science/01/01/leap.second.ap/index.html) > [@](#): > > At the National Institute for Science and Technology in Boulder, spokesman Fred McGehan said most scientists agree the Earth’s orbit around the sun has been gradually slowing for millennia. It appears that this hypothesis is based on 28 years of data where “leap seconds” were added to the last day of the year to synchronize our atomic calenders to the earth’s orbit. The last five years have bucked the trend with no extra “leap seconds” necessary. My questions are 1. Is there any other data to support this phenomenon? 2. Is this view really prevalent in the scientific community? TIA ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [January 2, 2004, 4:02pm UTC](https://boards.straightdope.com/t/is-the-earths-orbit-slowing-down/222294/2 "2004-01-02T16:02:43Z")
I think that article is _very_ badly written as is common with that type of articles which deal with science in the general media. AFAIK, the leap seconds are added not because the earth is slowing down but because it is irregular which is a totally different thing. The earth is irregular in its rotation about its axis and in its rotation about the sun due to causes known and unkonwn. Tides (of solid, liquid and gases) will slow orbiting bodies down. the moon is slowing down and I see nothing strange with the earth slowing down although at a much slower rate The article seems written by some reporter who is totally ignorant of the subject and jotted down a few gee-whiz words. Sounds more like the type of stuff you hear in a bar than something worthy of publication. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [January 2, 2004, 4:14pm UTC](https://boards.straightdope.com/t/is-the-earths-orbit-slowing-down/222294/3 "2004-01-02T16:14:26Z")
To expand a bit: Atomic time is kept by atomic clocks and is independent of the earth’s movement or other celestial bodies. It is “true” time in that it is a continuous count of seconds of time. Universal Time reflects, not true passing of time, but the geometrical position of the earth and the rest of the universe. If the earth slows down or speeds up then we just add or subtract seconds to keep Mean Solar “Time” in step with Atomic time. This is like saying the Queen will arrive at 5 o’clock and when the Queen is late we just set out clocks back and call the time of her arrival “5 o’clock”. ---
**Author:** ![swansont](https://avatars.discourse-cdn.com/v4/letter/s/5fc32e/32.png) [@swansont](https://boards.straightdope.com/u/swansont)\ **Post date:** [January 2, 2004, 4:24pm UTC](https://boards.straightdope.com/t/is-the-earths-orbit-slowing-down/222294/4 "2004-01-02T16:24:09Z")
The CNN article is horrible. Leap seconds were not added every year since 1972, and of the ones that were, not all were added at the the end of the year. The main slowdown mechanism is tidal friction, but there are many other effects. Overall, it’s impossible to predict what the rate will be. This is a rotational, not orbital effect. Redistribution of mass changes the moment of inertia, and hence the rotation rate, and lots of things can do this. Things like hurricanes and storms have angular momentum, which have to come from the rest of the earth, also affect the rate. We are still running slow, but the accumulated difference hasn’t gotten large enough to add a second. To say that we’ve stopped lagging is incorrect. IIRC the first atomic clock was ammonia, not cesium. But cesium provides better performance and is used in the majority of atomic frequency standards/clocks. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [January 2, 2004, 6:04pm UTC](https://boards.straightdope.com/t/is-the-earths-orbit-slowing-down/222294/5 "2004-01-02T18:04:55Z")
swansont, I agree with you that, contrary to what the article says, the main compensation is for rotational irregularities and not orbital but I did not want to disqualify that entirely because I thought there may be planetary interactions or other causes which may have some minor effect. Most science articles in the media are awful and have a gee-whiz tone which I hate. It may be acceptable when telling a story over some beers but it is totally unacceptable when reporting in the media. Unfortunately it happens all the time and we have threads criticizing them all the time. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [January 2, 2004, 6:31pm UTC](https://boards.straightdope.com/t/is-the-earths-orbit-slowing-down/222294/6 "2004-01-02T18:31:19Z")
Orbital irregularities will change the number of days in a year. I think you need to insert or delete whole days, not seconds, to correct for it. [pedant mode] It just occurred to me that “leap second” is not a very appropriate term. A _leap year_ is a year that’s longer than a regular year. The corresponding term should be _leap day_, defined as a day that’s longer than a regular day by one second (or more). [/p] ---
**Author:** ![Achernar](https://avatars.discourse-cdn.com/v4/letter/a/e274bd/32.png) [@Achernar](https://boards.straightdope.com/u/Achernar)\ **Post date:** [January 2, 2004, 7:03pm UTC](https://boards.straightdope.com/t/is-the-earths-orbit-slowing-down/222294/7 "2004-01-02T19:03:19Z")
I don’t know about that. When it exists, 29 Feb is called a “leap day”. It’s the day that’s added. So a leap second would be the second that’s added. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [January 2, 2004, 7:08pm UTC](https://boards.straightdope.com/t/is-the-earths-orbit-slowing-down/222294/8 "2004-01-02T19:08:44Z")
scr4, you, clearly, have no idea what you are talking about. Leap years insert an extra day to account for the fact that the length of the tropical year is not exactly divisible by the length of the day and has _nothing_ to do with orbital irregularities. ---
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [January 2, 2004, 7:26pm UTC](https://boards.straightdope.com/t/is-the-earths-orbit-slowing-down/222294/9 "2004-01-02T19:26:41Z")
Something else you should note, which underscores the difference between calendrical leap year corrections for tropical years, and the “leap second” corrections: The current Gregorian calendar still has about a day / 3000 years error in it, given the 4/100/400 leap year rule we use. This works out to 28.8 seconds / year, and is still an order of magnitude greater than error introduced by the variations in the Earth’s rotational speed. We simply aren’t concerned with keeping the calendar synchronized to that degree of accuracy. I think I mentioned in another thread that the former Soviet Union proposed such a correction, but nobody wanted to go along with it. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [January 2, 2004, 8:11pm UTC](https://boards.straightdope.com/t/is-the-earths-orbit-slowing-down/222294/10 "2004-01-02T20:11:27Z")
**sailor** , you originally said > [@](#): > > AFAIK, the leap seconds are added not because the earth is slowing down but because it is irregular which is a totally different thing. The earth is irregular in its rotation about its axis **and in its rotation about the sun** due to causes known and unkonwn. My comment was that the part I emphasized is not true. If there were any measurable orbital irregularities, the effect will be that the _orbital_ period of the earth will change, not _rotational_ period (length of day). Currently the orbital period is 365.242199 days; if the orbit were to shift, this number will change. The pattern of leap years is designed so that the average length of the calendar year matches that number. If you wanted to correct for orbital irregularities, you would correct for it by modifying the pattern of leap years. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [January 2, 2004, 8:12pm UTC](https://boards.straightdope.com/t/is-the-earths-orbit-slowing-down/222294/11 "2004-01-02T20:12:02Z")
> [@](#): > > \*Originally posted by Gold Dragon \* > It appears that this hypothesis is based on 28 years of data where “leap seconds” were added to the last day of the year to synchronize our atomic calenders to the earth’s orbit. Seconds may be added or subtracted from the months of December or June. > [@](#): > > In order to keep the cumulative difference in UT1-UTC less than 0.9 seconds, a leap second is added to the atomic time to decrease the difference between the two. This leap second can be either positive or negative depending on the Earth’s rotation. Since the first leap second in 1972, all leap seconds have been positive and there were 22 leap seconds in the 27 years to January, 1999.\_\_ This pattern reflects the general slowing trend of the Earth due to tidal braking. [Leap seconds](http://tycho.usno.navy.mil/leapsec.html) The [International Earth Rotation and Reference Systems Service (IERS)](http://www.iers.org/iers/) sends out a [bulletin in early July](http://hpiers.obspm.fr/eoppc/bul/bulc/bulletinc.dat) detailing their plans for year end clock adjustment. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [January 2, 2004, 10:33pm UTC](https://boards.straightdope.com/t/is-the-earths-orbit-slowing-down/222294/12 "2004-01-02T22:33:55Z")
scr4, if the earth slows in its orbit the length of the year will be longer and the legth of the day will be shorter. Please follow my explanation because it is interesting. The earth rotates about its axis not every 24 h but 23 h 56… m. the reason the mean sun takes 24 hrs to cross the local meridian is that the sun is falling behind a bit every day. While apparently the stars rotate 366.24… times per year, the sun revolves one time less: 365.24… The ratio 365.24…/366.24… is the ratio between the mean solar day and the mean sidereal day. Suppose the earth slowed down in its orbit and took 800 days to complete the orbit, while the sidereal day remains the same. Then the mean solar day would be 800/801 sidereal days.which is longer than what it is now. in other words, the constant rotation of the earth defines the sidereal day, not the solar day which depends on the length of the sidereal day and of the year. Any change in any of the two will change the solar day. In any case, the article is definitely badly written and the leap seconds account majorly for irregularities in the rotation and not for irregularities in the orbital motion as they say. We agree there. But I cannot rule out other effects and I was not ready to contradict the article to that extent. It could well be that even taking into account orbital irregularities they would never amount to a fraction of a second but i don’t know that. ---
**Author:** ![swansont](https://avatars.discourse-cdn.com/v4/letter/s/5fc32e/32.png) [@swansont](https://boards.straightdope.com/u/swansont)\ **Post date:** [January 3, 2004, 12:59am UTC](https://boards.straightdope.com/t/is-the-earths-orbit-slowing-down/222294/13 "2004-01-03T00:59:55Z")
> [@](#): > > \*Originally posted by Squink \* > Seconds may be added or subtracted from the months of December or June. Actually they can be added any month, but preference is given to December and June, then March and September. Thus far, all have been added in December or June. ---
**Author:** ![GorillaMan](https://avatars.discourse-cdn.com/v4/letter/g/50afbb/32.png) [@GorillaMan](https://boards.straightdope.com/u/GorillaMan)\ **Post date:** [January 3, 2004, 1:08am UTC](https://boards.straightdope.com/t/is-the-earths-orbit-slowing-down/222294/14 "2004-01-03T01:08:31Z")
Did anyone read the headline of the article? “EARTH ORBIT SLOWS NO MORE, baffling scientists”?..the journalist didn’t claim that the earth is slowing down, just decided to make scientists look fools, which is easy if you use the gift of bullshit ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [January 3, 2004, 1:10am UTC](https://boards.straightdope.com/t/is-the-earths-orbit-slowing-down/222294/15 "2004-01-03T01:10:31Z")
I used to keep track of the rate of several timepices (for celestial navigation) and the leap seconds would throw me totally out of whack if I forgot to account for them. ---
**Author:** ![robo99](https://avatars.discourse-cdn.com/v4/letter/r/a8b319/32.png) [@robo99](https://boards.straightdope.com/u/robo99)\ **Post date:** [January 3, 2004, 1:12am UTC](https://boards.straightdope.com/t/is-the-earths-orbit-slowing-down/222294/16 "2004-01-03T01:12:24Z")
Here’s another tack. Since the Sun is constantly expelling mass shouldn’t that mean that over the lifespan of the solar system the planets’ orbits should slow down? Or is this too insignificant an effect? ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [January 3, 2004, 3:27am UTC](https://boards.straightdope.com/t/is-the-earths-orbit-slowing-down/222294/17 "2004-01-03T03:27:40Z")
> [@](#): > > \*Originally posted by sailor \* > **Suppose the earth slowed down in its orbit and took 800 days to complete the orbit, while the sidereal day remains the same. Then the mean solar day would be 800/801 sidereal days.which is longer than what it is now.** OK, you are right. I just thought that since rotational irregularities are much larger than orbital irregularities, the second-order effect of orbital irregularities isn’t worth talking about. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [January 3, 2004, 3:59am UTC](https://boards.straightdope.com/t/is-the-earths-orbit-slowing-down/222294/18 "2004-01-03T03:59:18Z")
> [@](#): > > \*Originally posted by scr4 \* > \*\*OK, you are right. I just thought that since rotational irregularities are much larger than orbital irregularities, the second-order effect of orbital irregularities isn’t worth talking about. \*\* I agree with you there but the news article got it all wrong and talks about orbital variations. Just goes to show you the person who wrote it does not have a clue.