12
$\begingroup$

If Sun-Jupiter baricentre is outside the Sun, does that mean the Sun is orbiting around that point too right?

Then the Sun shouldn't be nearer to the Earth at some point during the Sun-Jupiter orbit (and also farther at the opposite point)?

Sun-Jupiter orbit completes every 11.86 Earth years, so why we don't (or yes we do?) have cycles with hot/cold weather every 6 years?

$\endgroup$
17
$\begingroup$

If you want to model the entire solar system, it's best to model the Sun, the planets, the asteroids, etc. with respect to the barycenter. That choice reduces the equations of motion to their simplest form. Note well: That "simplest form" is not all that simple if one chooses to incorporate relativistic effects into the equations of motion.

On the other hand, if you want to model the behavior of a single planet, and especially the inner terrestrial planets, it's best to model the planet as orbiting the Sun, with the other planets slightly perturbing the orbit of the planet in question. Stealing from an answer to a related question I wrote on physics.SE, the image below depicts the orbit of Venus about the Sun (red curve) and the orbit of Venus about the solar system barycenter (black curve). The horizontal axis is time in days from noon on 1 January 2000. The vertical axis is distance from the Sun (red curve) and distance from the barycenter (black curve).

Orbit of Venus about the Sun (red curve) vs. orbit of Venus about the solar system barycenter (black curve). See surrounding text.

It's pretty clear from the above graph that it is better, at least for the short term, to model terrestrial planets as orbiting the Sun. Over longer spans of time, the other planets in the solar system perturb the orbit of a terrestrial planet. The greatest of these perturbations is to make the orbit precess. The relativistic precession of Mercury is less than a tenth of the Mercury's non-relativistic precession due to perturbations from other planets.

$\endgroup$
7
  • 2
    $\begingroup$ Just to drive home the point that the OP was asking about: how much do the perihelion & aphelion distances of Venus (the peaks & valleys of the red curve) actually vary? It's hard to tell from this graph. $\endgroup$ Sep 13 at 13:25
  • $\begingroup$ @MichaelSeifert The scale goes from 0.71 AU (106.214.488 km) to 0.74 AU (110.702.424 km), so spans 4.487.936 km. For comparison: The sun has a radius of 696.342 km, so the scale is about 3,2 suns wide, so each horizontal segment is (roughly) 1/2 sun disks wide. Does that help? $\endgroup$ Sep 13 at 20:06
  • 1
    $\begingroup$ @AngeloFuchs: No, I was asking about whether there were any differences between the peaks of the red graph. They all appear to be at about 0.728 AU, and it's hard to differentiate between they on the scale of the graph. The OP's question is specifically about whether there are differences on a planet's distance to the Sun over time due to the effects of other planets; this graph seems to indicate they're small, but I was curious how small. $\endgroup$ Sep 13 at 20:18
  • $\begingroup$ @MichaelSeifert The aphelia do not differ that much, but the distance to the sun differs by about one solar diameter from aphelion (0,728) to perihelion (0.718). The distance of Venus to the Sun in dependence of the other planets differ marginally and can not be seen on this graph. What can be seen is that the sun (as primary masspoint for Venus) moves noticeably around the barycenter of the solar system and takes Venus with it. So to answer the original question: No, the sun is not (noticeably) closer to earth because of Jupiter. $\endgroup$ Sep 13 at 20:45
  • $\begingroup$ The paper discussed here "contended that the motion of the Sun around the barycentres created by the gas giants was enough to alter the distance between Earth and Sun by up to 3 million kilometres". $\endgroup$ Sep 13 at 22:59
3
$\begingroup$

We would see some variation. The sun orbits the barycenter of our solar system (roughly the barycenter of Sun-Juptiter) at a radius of 742,000 km. This is a variation of roughly 0.5% of the orbital distance of the Earth from the sun.

The Earth is also in an elliptical orbit. The perihelion and aphelion are 5,000,000km apart, about 3.3% of the orbital distance from the Earth to the sun. And its worth remembering that this is not what causes most of our cycles of weather. We are furthest from the sun in June, which is summer in the Northern hemisphere. Weather cycles are more driven by the tilt of the planet.

It would be difficult to find solid environmental evidence of this cycle. The sun happens to go through a 11 year cycle where its output varies by 0.1%. We do indeed see a warming and cooling effect at the extremes of the cycle. The variation from maximum to minimum is about 0.18K, and this effect is applied for a peak that is measured in years rather than one that is measured in months. Research on the solar effects is ongoing and complicated. For instance, there are hypotheses that the solar cycle may change cloud cover, which would make detecting the nearby 11.86 year cycle more tricky.

$\endgroup$
7
  • 6
    $\begingroup$ Actually this isn't really correct yet. Since Jupiter is ~5.5 AU away from the Sun and ~4.5 to ~6.5 away from the Earth, it affects both of them roughly similarly. What that means is that the Earth's orbit tracks the Sun's center much more closely than it does the Sun-Jupiter barycenter, and so the effect is a lot less than your current 0.5%. $\endgroup$
    – uhoh
    Sep 13 at 0:36
  • $\begingroup$ @uhoh: "Roughly" is doing some work in your first sentence. The gravitational acceleration of a body at 4.5 AU is about 50% larger than that of a body at 5.5 AU. $\endgroup$ Sep 13 at 20:20
  • 1
    $\begingroup$ @MichaelSeifert I like to make words to some heavy lifting from time to time; it's what they're for! :-) $\endgroup$
    – uhoh
    Sep 13 at 20:49
  • $\begingroup$ Wait, the sun orbits the Solar System's barycenter every 11 years, and there's an 11 year cycle of solar output? Are they related, by any chance? $\endgroup$
    – nick012000
    Sep 14 at 5:57
  • $\begingroup$ @nick012000 don't wait i.stack.imgur.com/NRSJx.png $\endgroup$
    – uhoh
    Sep 14 at 6:05

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.