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stitt29
2009-Aug-12, 03:08 PM
Hi,

I read that Earth's anomalistic year has increased by 0.1365seconds in the last century. does anyone know if the other planets of the solar system's anomalistic years are also increasing? Also any links to where I can get details on this

thoth II
2009-Aug-12, 04:37 PM
my guess would be, if we examine why the earth's anolmalistic year is increasing, we'll get a clue. If the year is increasing, the orbit is changing. Why? it must have to do with gravitational interactions with other bodies in the solar system. Using that reasoning, all the planet's orbits would be similarly affected, and thus their periods would change a little. Make sense BAUT people?

stitt29
2009-Aug-14, 08:52 AM
Yes, but has the anomalistic years of other planets been measured? Does anyone have data on this?

antoniseb
2009-Aug-14, 04:22 PM
Yes, but has the anomalistic years of other planets been measured? Does anyone have data on this?

It might be tough to measure with that kind of precision for any other planet until we put some serious observatories on them.

I suspect the future will show that Earth's rapid rotation and liquid core make it move away from the Sun faster than the other terrestrials. Measuring it for a planet with no hard surface will be trickier.

hhEb09'1
2009-Aug-14, 04:52 PM
my guess would be, if we examine why the earth's anolmalistic year is increasing, we'll get a clue. If the year is increasing, the orbit is changing. Why? it must have to do with gravitational interactions with other bodies in the solar system. Using that reasoning, all the planet's orbits would be similarly affected, and thus their periods would change a little. Make sense BAUT people?The anomalistic year can change without the period changing, right?

thoth II
2009-Aug-14, 05:27 PM
The anomalistic year can change without the period changing, right?

I'm not sure, but I would guess so. Maybe someone on the forum with a speciality in orbital mechanics would know the precise detail.

DrRocket
2009-Aug-14, 05:31 PM
my guess would be, if we examine why the earth's anolmalistic year is increasing, we'll get a clue. If the year is increasing, the orbit is changing. Why? it must have to do with gravitational interactions with other bodies in the solar system. Using that reasoning, all the planet's orbits would be similarly affected, and thus their periods would change a little. Make sense BAUT people?

The orbit is not and never has been a perfect ellipse. If it were there could be no such thing as the precession of the perihellion.

That means that the orbit is not, strictly speaking, periodic. This in turn calls into question what you mean by "changing".

If you mean by "changing" departing from a Keplerian approxiimation, then it is changing. But Keplerian orbits are calculated on the basis of a two-body problem and, as you noted there are more than two bodies in the solar system. Hence, "changing" in this sense ought not be a surprise.

Personally I have not noticed the .1365 second difference. I guess I need to get my watch re-calibrated.

tony873004
2009-Aug-14, 05:59 PM
The anomalistic year can change without the period changing, right?
Yes. The anomolistic year can change without the orbital period changing. An anomalistic year is the time from one perihelion passage to the next. Since the longitude of the perihelions of the planets are not fixed, they drift slowly (measured in arcseconds per century). This is due to perturbations, mostly from the other planets. The most famous example is the precession of perihelion of Mercury. The computed amount differed slightly from the observed amount. It took Einstein's relativity to explain the descrepancy.

If the precession of perihelion was constant, then the time between perihelion passages would be constant too. But if the drift accelerates, then the time between perihelion passages shifts, and the period of the anomolistic year changes.

The amount of drift can be computed analytically, like the way scientists computed the precession of perihelion for Mercury, but computing it multiple times to see how it changes over time. Or it can be done numerically.

astromark
2009-Aug-16, 10:05 AM
Firstly could we please get into the habit of stating numbers that are expressed as fractions of a whole number, should be expressed as 0.1365 and not as .1365 This so very small fraction of a secound it may not actually be outside the margin of error normally built into these purely mathematical summaries of what might not be so. No I am not about to dispute the findings of some scientific annalist. I am just raising the awareness that all may not be so clear. 0.1365 seconds per 100 years is not to be unexpected if you consider that we already know the Earth is actually moving away from the Sun by as much as 8cm per year... and no that number has little bearing on this as facts go attitude we encourage here. I have used it only to demonstraight a point.

mugaliens
2009-Aug-17, 05:42 AM
I'm not sure, but I would guess so. Maybe someone on the forum with a speciality in orbital mechanics would know the precise detail.

From Wikipedia:


The anomalistic year is the time taken for the Earth to complete one revolution with respect to its apsides (http://en.wikipedia.org/wiki/Apsis). The orbit of the Earth is elliptical; the extreme points, called apsides, are the perihelion (http://en.wikipedia.org/wiki/Perihelion), where the Earth is closest to the Sun (January 3 (http://en.wikipedia.org/wiki/January_3) in 2010 (http://en.wikipedia.org/wiki/2010)), and the aphelion (http://en.wikipedia.org/wiki/Aphelion), where the Earth is farthest from the Sun (July 6 (http://en.wikipedia.org/wiki/July_6) in 2010). The anomalistic year is usually defined as the time between two successive perihelion passages. Its average duration is:
365.259 635 864 days (365 d 6 h 13 min 52 s) (at the epoch J2000.0). The anomalistic year is slightly longer than the sidereal year because of the precession of the apsides (or anomalistic precession (http://en.wikipedia.org/wiki/Precession_(astronomy)#Anomalistic_precession)).