Remember Me?

 Straight Dope Message Board Remember Me?

#1
06-13-2018, 12:51 PM
 Charter Member Join Date: Aug 2001 Posts: 16,913

## Why does Jupiter NOT effect global warming?

I was watching a documentary about astronomy. In it, the narrator claimed that Jupiter can make the sun shift by as much as 500-thousand miles.

So that must mean, when Jupiter is in alignment with Earth, the sun is now 500-thousand miles closer to it. That seems like a lot! Certainly enough to cause significant change.

Am I missing something here?

[FTR: I believe what climatologists are saying about global warming. This thread is not intended as a "Gotcha" or anything silly like that. )
#2
06-13-2018, 01:14 PM
 Guest Join Date: Mar 2000 Location: hobgoblin of geographers Posts: 4,404
Mostly because of the Inverse Square Law...

Let's do a thought experiment with numbers that are based in reality, but not exquisitely accurate because, as you might see, the differences are almost irrelevant.

Assume the Earth is 92 million miles from the Sun (it is on average)

The Inverse Square Law governs how much radiation emitted from the sun impacts the Earth - a factor in this calculation will be 1/(distance2)... put in 92 million miles as the distance and the factor is 1.18 * 10-16

Now assume Jupiter changes that distance to the sun by 500,000 miles. Put in 92.5 million miles, and the factor is 1.17 * 10-16

The difference is very small compared to the total distance between the Earth and the Sun.

A couple other factors that may be less important that impact on your question are that Jupiter has been present for hundreds of thousands of years, and so its effects on the climate (as small as they are) already were factored in before humans started adding more greenhouse gases to the atmosphere. Another is that Jupiter and Earth will be aligned only during a small portion of the year, when they happen to line up on the same side (or opposite sides) of the sun, so its effects would be minimal during other parts of the year.

Last edited by wevets; 06-13-2018 at 01:19 PM. Reason: added parenthetical expression
#3
06-13-2018, 01:19 PM
 Guest Join Date: Mar 1999 Location: NC Posts: 1,740
Possibly relevant:
https://www.smithsonianmag.com/smart...cle-180969038/
#4
06-13-2018, 01:29 PM
 Guest Join Date: Feb 2007 Location: Challenger Deep Posts: 12,715
Quote:
 Originally Posted by wevets Another is that Jupiter and Earth will be aligned only during a small portion of the year, when they happen to line up on the same side (or opposite sides) of the sun, so its effects would be minimal during other parts of the year.
Not just minimal, but opposite. Jupiter's orbital period is about 12 years, so Earth completes an orbit while Jupiter hasn't moved very far; this results in a cycle of "sun is closer than average" followed by "sun is farther than average" repeating with a period of just over a year. IOW, any effect due to Jupiter jerking the sun around it is cyclic and occurs on a timescale far shorter than climate change is happening.
#5
06-13-2018, 01:35 PM
 Guest Join Date: Nov 2009 Location: Eugene, Oregon Posts: 1,350
What makes you think that Jupiter does not affect global warming?

According to this scientific paper, the effect caused by Earth's alignment with Jupiter accounts for +/- 2.5 degrees C, but that effect is swamped by the much larger effect of Earth's tilt which swings from about +20 to -10. Sometimes the two effects are in sync and add up; other times they're out of sync and partially cancel each other out. But both of them are background noise when you're trying to measure tiny increases in the global average over a span of decades.

You might as well ask the question "Why doesn't wind affect the speed of runners doing laps around a track?". The correct answer is that wind DOES affect their speed, causing them to slow down when running into a headwind and speed up running with a tail wind. But it's hardly worth paying attention to if the race involves several laps around the track and you only care about the finish time, i.e. average speed. Yeah, if you measured the split times for each 100-meter section of the race you'd see slight increases and decreases due to which way the wind is blowing, but over the whole race it averages out.

So, yes, Jupiter affects the global average temperature of Earth at any one time but the effect will average out when you're measuring across decades.

Last edited by sbunny8; 06-13-2018 at 01:36 PM. Reason: typo
#6
06-13-2018, 01:35 PM
 Guest Join Date: Mar 2000 Location: hobgoblin of geographers Posts: 4,404
Good point - if Earth, the Sun, and Jupiter are aligned in April to have the Sun closer to Earth - they will be aligned again the next May or so with an opposite effect, the Sun further away from Earth.
#7
06-13-2018, 01:48 PM
 Robot Mod in Beta Testing Moderator Join Date: Mar 2001 Location: Pennsylvania Posts: 26,265
The sun also isn't constant. It tends to cycle between what we call the solar minimum and solar maximum on roughly an 11 year cycle (it varies, sometimes as short as 8 or 9 years and sometimes as long as 14 or so, the average is 11).

This solar cycle does affect the average global temperature, and has been linked to some changes in weather patterns.

As far as global warming goes, though, while the solar cycle does affect the Earth's temperature, it's just a periodic effect. The Earth will get slightly warmer and slightly cooler based on where the sun is in its cycle, but at the end of the cycle it will be back to where it started, temperature-wise.

Any effect Jupiter might have on the Earth's temperature would be similarly cyclical, and would not contribute to global warming, which is a constant increase in global temperature that has been observed for centuries.
#8
06-13-2018, 01:50 PM
 Guest Join Date: Apr 2000 Location: Chicago, IL USA Posts: 21,325
Quote:
 Originally Posted by wevets Assume the Earth is 92 million miles from the Sun (it is on average)
That or we can note that the earth at perihelion is 91.4 million miles from the Sun and 94.5 million miles at aphelion. A difference of 3.1 million miles which is a lot more than the 500,000 miles in the OP and it happens every year.

Last edited by Whack-a-Mole; 06-13-2018 at 01:52 PM.
#9
06-13-2018, 01:59 PM
 Guest Join Date: Nov 2009 Location: Eugene, Oregon Posts: 1,350
Quote:
 Originally Posted by wevets Assume the Earth is 92 million miles from the Sun (it is on average) The Inverse Square Law governs how much radiation emitted from the sun impacts the Earth - a factor in this calculation will be 1/(distance2)... put in 92 million miles as the distance and the factor is 1.18 * 10-16 Now assume Jupiter changes that distance to the sun by 500,000 miles. Put in 92.5 million miles, and the factor is 1.17 * 10-16 The difference is very small compared to the total distance between the Earth and the Sun.
No, the inverse square law makes it worse. If the decrease were linear, you'd expect a difference of about 1%. But because the of the inverse square law, the difference is more than 2%.

Comparing 1.18E-16 to 1.17E-16 isn't helpful. Let's look at it this way. At 92 million miles, Earth intercepts 174 petawatts from the sun. At 92.5 million miles, it's 172.1 petawatts. At 91.5 million miles, it's 175.9 petawatts. That's a difference of about 2.2%. Now consider the fact that Earth's average temperature is about 288 Kelvin. Increase that by 2.2% and you'd have 294.36 Kelvin, which is an increase of more than 11 degrees Fahrenheit. That's the difference between living in Pensacola Florida vs. Washington DC.
#10
06-13-2018, 02:15 PM
 Guest Join Date: Jul 2013 Posts: 11,590
Quote:
 Originally Posted by sbunny8 No, the inverse square law makes it worse. If the decrease were linear, you'd expect a difference of about 1%. But because the of the inverse square law, the difference is more than 2%. Comparing 1.18E-16 to 1.17E-16 isn't helpful. Let's look at it this way. At 92 million miles, Earth intercepts 174 petawatts from the sun. At 92.5 million miles, it's 172.1 petawatts. At 91.5 million miles, it's 175.9 petawatts. That's a difference of about 2.2%. Now consider the fact that Earth's average temperature is about 288 Kelvin. Increase that by 2.2% and you'd have 294.36 Kelvin, which is an increase of more than 11 degrees Fahrenheit. That's the difference between living in Pensacola Florida vs. Washington DC.
Increasing the rate of incoming flux to a radiating object does not increase its temperature linearly.

Last edited by k9bfriender; 06-13-2018 at 02:16 PM.
#11
06-13-2018, 02:21 PM
 Charter Member Join Date: Jul 2000 Location: America's Wing Posts: 31,004
Global warming exists already, there's no way that Jupiter can effect it.
#12
06-13-2018, 02:55 PM
 Member Join Date: Mar 2004 Location: Howdy Posts: 22,681
For the record, the heat output of the sun (solar irradiation) is tracked by NASA (and, presumably, other space agencies) and is factored in to models of the climate.

The average global temperature does rise and fall with solar irradiation to a notable extent and the fact that solar irradiance was on the rise during (if I recall correctly) the 90s made it more difficult to determine whether global warming was human caused or not. But with more data, volcanic events, a reduction is solar irradiance, etc. the exact proportions are now (I believe) fairly well locked in.
#13
06-13-2018, 03:02 PM
 Charter Member Moderator Join Date: Jan 2000 Location: The Land of Cleves Posts: 87,266
One point that hasn't been raised yet is that the Earth does not orbit around the Solar System barycenter. When Jupiter pulls the Sun around, the Earth mostly moves along with the Sun. So the distance won't vary by nearly as much as folks are saying.
#14
06-13-2018, 03:03 PM
 Guest Join Date: Dec 2009 Location: State of Jefferson Posts: 8,499
This is why we use 50 year time intervals for our climatic averages ... comparing the past 50 years with the previous 50 years will "average out" the effects of Jupiter's orbit, solar cycles, El Nino/La Nina cycles and whatever else that causes changes in only ten or twenty year cycles ...
#15
06-13-2018, 03:23 PM
 Member Join Date: Feb 2001 Location: Not the PNW :-( Posts: 21,599
Quote:
 Originally Posted by awldune Possibly relevant: https://www.smithsonianmag.com/smart...cle-180969038/
This was what I was going to point out. Part of the Milankovitch cycle is induced by Jupiter and Saturn.

But we are talking about effects over tens of thousands of years. Not anywhere close to explaining what's been going on the last 50 years.

No known astronomical effect can explain recent changes. The time scale is either too long or it's a too short term cycle. And ignoring the coincidental increase in CO2 is ridiculous.

It's like letting someone off for murder since people die naturally all the time.
#16
06-13-2018, 03:30 PM
 Member Join Date: Oct 2000 Posts: 7,263
Quote:
 Originally Posted by Chronos One point that hasn't been raised yet is that the Earth does not orbit around the Solar System barycenter. When Jupiter pulls the Sun around, the Earth mostly moves along with the Sun. So the distance won't vary by nearly as much as folks are saying.
Thank you for this - I was just about to post something similar.
#17
06-13-2018, 06:43 PM
 Member Join Date: Oct 2000 Posts: 7,263
I've had a little more time to think. 500,000 miles is the amount that the Sun is deflected by Jupiter from the Sun's ordinary path through the Galaxy (an observer on a distant star would see this deviation from the relatively straight path the Sun would normally take - if the distant star were properly oriented relative to the plane of the ecliptic) - it's easy to see why, since Jupiter is about 500 million miles from the Sun and has about 1,000th the mass of the Sun. But in the first order, the Earth is pulled the same amount by Jupiter as the Sun is, so Jupiter causes no deviation of the distance from the Earth to the Sun to that order - we have to go to higher order effects to see Jupiter's effect. I'd expect it to be a tidal effect, so I'd expect the magnitude of the effect of Jupiter on the Earth's distance to the Sun to be proportional to 1 over (5 to the 3rd power) (or 1/125), since Jupiter is on average 5 times as far from Earth as the Sun is - so we're looking at something like a 4,000 mile effect, not a 500,000 mile effect (all this is "back of the envelope" - it might be off by a factor of 3 either way).
#18
06-14-2018, 09:08 AM
 Guest Join Date: Nov 2009 Location: Eugene, Oregon Posts: 1,350
Quote:
 Originally Posted by sbunny8 According to this scientific paper, the effect caused by Earth's alignment with Jupiter accounts for +/- 2.5 degrees C, but that effect is swamped by the much larger effect of Earth's tilt which swings from about +20 to -10. Sometimes the two effects are in sync and add up; other times they're out of sync and partially cancel each other out. But both of them are background noise when you're trying to measure tiny increases in the global average over a span of decades.
I would like to retract that cite. Upon further examination, I am convinced that it's not really a scientific paper, not based on scientific research, and not peer-reviewed. It looks like pseudo-science to me. Some of what it says is probably accurate, but I no longer trust it as a source.

However, I stand by my statement that fluctuations up and down over a period of months will be washed out when looking at a long-term trend over years and decades. Strictly speaking, the position of Jupiter might affect Earth's Global Average Temperature, but Global Warming isn't just about GAT, it's about the upward trend of GAT measured on a time scale of years and decades. Imagine a business that makes more profit in the summer time and less profit in the winter time. If you are trying to determine whether the business is more profitable now that it was fifteen years ago, the summer-winter fluctuation would be irrelevant. It doesn't even matter whether you plot the yearly averages or the monthly averages, as long as your x-axis includes an equal number of summers and winters.

Quote:
 Originally Posted by Chronos One point that hasn't been raised yet is that the Earth does not orbit around the Solar System barycenter. When Jupiter pulls the Sun around, the Earth mostly moves along with the Sun. So the distance won't vary by nearly as much as folks are saying.
cite? This seems counter-intuitive to me. According to this NASA web page, all the planets (including Earth) orbit around the solar system's barycenter. Granted, this web page looks like it was written for a sixth grade text book, but I still would expect it to have accurate information.
#19
06-14-2018, 10:55 AM
 Guest Join Date: Jun 2000 Location: Dallas, TX Posts: 19,372
Another thing to consider is that the normal difference between summer and winter distances from the sun is 3 million miles - 6 times larger than anything Jupiter does.

And... the Earth is closer during winter in the northern hemisphere, and farther away during summer, but the actual angle of incidence of the sunlight far outweighs that small amount of distance, making summer hotter because the light hits more directly, despite being 3 million miles further away.
#20
06-14-2018, 11:18 AM
 Member Join Date: Oct 2000 Posts: 7,263
Quote:
 Originally Posted by sbunny8 According to this NASA web page, all the planets (including Earth) orbit around the solar system's barycenter. Granted, this web page looks like it was written for a sixth grade text book, but I still would expect it to have accurate information.
I think that that page is seriously mistaken (or at least, poorly worded enough to be seriously misleading). It's far to say that the Earth orbits the Earth-Sun barycenter - that's a convenient reference frame to use for some purposes, but to say that it orbits the Sun-Jupiter barycenter is just wrong.
#21
06-14-2018, 05:29 PM
 Guest Join Date: Nov 2009 Location: Eugene, Oregon Posts: 1,350
Quote:
 Originally Posted by Andy L I think that that page is seriously mistaken (or at least, poorly worded enough to be seriously misleading). It's far to say that the Earth orbits the Earth-Sun barycenter - that's a convenient reference frame to use for some purposes, but to say that it orbits the Sun-Jupiter barycenter is just wrong.
Actually, the web page I cited doesn't say Earth orbits the Sun-Jupiter barycenter. It says Earth orbits the solar system's barycenter (which is pretty close to the Sun-Jupiter barycenter but it's not the same thing).

Can you point me to a web page that agrees with you that this statement "is just wrong" [your words]? Because I googled the question "Earth orbits the barycenter of what?". Naturally, there are multiple sources which completely ignore the barycenter and merely say that Earth orbits the Sun. I also found several sources which ignore the rest of the solar system and talk about the Earth-Sun barycenter. But looked at five who discussed the solar system's barycenter and all five of them said yes the Sun and Earth and all the objects in the solar system orbit the barycenter of the solar system. I can't find a single source (outside this thread) that says the solar system has a barycenter but Earth doesn't orbit it.
#22
06-14-2018, 06:03 PM
 Charter Member Moderator Join Date: Jan 2000 Location: The Land of Cleves Posts: 87,266
But you could also say that the Earth orbits the Earth-Moon barycenter. And what barycenter does the Moon orbit around?

Objects behaving like all of their mass is at the center of mass only works when the mass distributions are spherically symmetric. The Solar System isn't.
#23
06-14-2018, 06:27 PM
 Guest Join Date: Aug 2012 Location: Frogstar World B Posts: 17,169
Quote:
 Originally Posted by Grrr! So that must mean, when Jupiter is in alignment with Earth, the sun is now 500-thousand miles closer to it.
Depends on what you mean by “alignment”. The Jupiter/Sun barycenter is above the “surface” of the sun by thousands of miles. This is the point that the two orbit around. Thus, if Jupiter and Earth are in alignment (shortest distance between them), I would expect the Sun to be farther away, not closer.
#24
06-14-2018, 06:30 PM
 Guest Join Date: Aug 2012 Location: Frogstar World B Posts: 17,169
Quote:
 Originally Posted by Chronos But you could also say that the Earth orbits the Earth-Moon barycenter. And what barycenter does the Moon orbit around?
The Earth/Moon barycenter goes through the body of the Earth (about a thousand miles down from the surface closest to the moon), so one would say Earth rotates around it while the moon orbits it.
#25
06-14-2018, 06:31 PM
 Charter Member Join Date: Jan 2004 Location: Albany/Corvallis, OR Posts: 4,811
Quote:
 Originally Posted by Ludovic Global warming exists already, there's no way that Jupiter can effect it.
There's basically no thread that can't be improved by a grammar joke.
#26
06-14-2018, 06:42 PM
 Guest Join Date: Aug 2012 Location: Frogstar World B Posts: 17,169
Here is a diagram of the track of the solar system barycenter (center of mass) over the years. All the planets have an affect on its location.
#27
06-14-2018, 07:14 PM
 Guest Join Date: Nov 2009 Location: Eugene, Oregon Posts: 1,350
Quote:
 Originally Posted by Chronos But you could also say that the Earth orbits the Earth-Moon barycenter. And what barycenter does the Moon orbit around?
My answer: On a short time scale of weeks, Earth and Luna orbit the Earth-Luna barycenter. But on a longer time scale of months, both Earth and Luna are orbiting the barycenter of the solar system. Luna's orbit around the solar system is a series of a dozen or so loops whose center is the barycenter of the solar system. On an even longer time scale of MegaYears, everything in our Galaxy, including Luna, is orbiting the barycenter of the Galaxy. It just makes lots of little loops and twirls along the way.
#28
06-14-2018, 07:33 PM
 Guest Join Date: Dec 2009 Location: State of Jefferson Posts: 8,499
Quote:
 Originally Posted by Chronos But you could also say that the Earth orbits the Earth-Moon barycenter. And what barycenter does the Moon orbit around? Objects behaving like all of their mass is at the center of mass only works when the mass distributions are spherically symmetric. The Solar System isn't.
This kinda caught me off-guard as well ... my understanding is that if we treat the Earth and Moon as point-sources of force, then these two points orbit around the barycenter of this system, and it's the barycenter that orbits the Sun ... meaning the Earth wobbles a bit as it revolves around the Sun ...

Then, by extension to a 12 or 18 body system, each of these body's force vector is pointed at the combined barycenter of the whole system ... just add the forces from the Sun, Jupiter, Saturn etc etc etc (as measured from the Earth/Moon barycenter) and this should point to the solar system's barycenter, not the center of gravity of the Sun ...

Why would all these 18 point sources of gravity have be symmetric relative to each other? ... they are symmetric within themselves but I don't see the need for them to be symmetric to each other ...

... or does this have to do with the near impossibility of solving the 18-body gravity equations? ...
#29
06-14-2018, 07:57 PM
 Charter Member Join Date: Oct 1999 Location: Sturgeon Bay, WI USA Posts: 21,770
Quote:
 Originally Posted by sbunny8 I would like to retract that cite. Upon further examination, I am convinced that it's not really a scientific paper, not based on scientific research, and not peer-reviewed. It looks like pseudo-science to me. Some of what it says is probably accurate, but I no longer trust it as a source.
I am not questioning your judgement in the slightest, but I am interested in knowing how you made your determination. Can you shed some light on this (PM me if you prefer)?
#30
06-15-2018, 05:51 AM
 Charter Member Join Date: Jan 2000 Location: My own private Nogero Posts: 7,637
Quote:
 Originally Posted by wevets Good point - if Earth, the Sun, and Jupiter are aligned in April to have the Sun closer to Earth - they will be aligned again the next May or so with an opposite effect, the Sun further away from Earth.
You have the period too long by a factor of 2. Jupiter's period is 12 years. So if its opposition (point where it's in the opposite direction from the sun) is in April, a year later when the Earth comes around to opposition again, Jupiter will have traveled 1/12th of its orbit. So Earth has to travel 1/12th of an additional orbit to catch up. That is, an extra month, so the opposition will be in May in this case. So for Jupiter, the period from one opposition to the next (the synodic period) is 13 months. The conjuction point (point where Jupiter is in the same direction as the Sun) will be half that, 6 1/2 months after opposition. In this case, that'll be in October or November.
#31
06-15-2018, 07:06 AM
 Charter Member Join Date: Apr 2004 Location: Europe Posts: 811
Quote:
 Originally Posted by Grrr! I was watching a documentary about astronomy. In it, the narrator claimed that Jupiter can make the sun shift by as much as 500-thousand miles. So that must mean, when Jupiter is in alignment with Earth, the sun is now 500-thousand miles closer to it.
Isn't this simply a complete misunderstanding?

The Earth is a small speck that orbits the sun, with distant Jupiter pulling on the whole set. So to a first approximation, Jupiter pulls BOTH Sun and Earth closer to it, with no effect on the Earth-Sun distance.

To a second approximation, there would be the tidal effects. Tidal effects always pull a body apart. So Jupiter actually pulls the Earth and Sun apart from each other periodically by a very very tiny amount, with a 6 month period.

(I think this is what Andy L is saying.)

Am I missing something?

Last edited by Frankenstein Monster; 06-15-2018 at 07:09 AM.
#32
06-15-2018, 07:26 AM
 Member Join Date: Feb 2001 Location: Not the PNW :-( Posts: 21,599
Quote:
 Originally Posted by sbunny8 My answer: On a short time scale of weeks, Earth and Luna orbit the Earth-Luna barycenter. But on a longer time scale of months, both Earth and Luna are orbiting the barycenter of the solar system. Luna's orbit around the solar system is a series of a dozen or so loops whose center is the barycenter of the solar system. ...
Note that from the point of view of the Moon's orbit around the Sun it is not a bunch of loops. If you draw the Moon's orbit around the Sun you get something fairly close to a circle (okay, an ellipse). It is everywhere concave. Not remotely loopy.
#33
06-15-2018, 08:07 AM
 Charter Member Moderator Join Date: Jan 2000 Location: The Land of Cleves Posts: 87,266
Stand on the surface of the Moon, right in the middle of the Earth-facing side. The Earth-Moon barycenter will be directly above you. The Moon will be directly below you. If you let go of something, which way does it fall, towards the barycenter or towards the Moon?

The net force vectors don't all point to the barycenter. I can't explain why they don't, because there's no reason why they would. Individual components of the net force point towards individual objects, and then you add up all of those components to get the net force.
#34
06-15-2018, 04:41 PM
 Member Join Date: Oct 2000 Posts: 7,263
Quote:
 Originally Posted by sbunny8 Actually, the web page I cited doesn't say Earth orbits the Sun-Jupiter barycenter. It says Earth orbits the solar system's barycenter (which is pretty close to the Sun-Jupiter barycenter but it's not the same thing). Can you point me to a web page that agrees with you that this statement "is just wrong" [your words]? Because I googled the question "Earth orbits the barycenter of what?". Naturally, there are multiple sources which completely ignore the barycenter and merely say that Earth orbits the Sun. I also found several sources which ignore the rest of the solar system and talk about the Earth-Sun barycenter. But looked at five who discussed the solar system's barycenter and all five of them said yes the Sun and Earth and all the objects in the solar system orbit the barycenter of the solar system. I can't find a single source (outside this thread) that says the solar system has a barycenter but Earth doesn't orbit it.
I've been looking for a good cite. I think Chronos and Frankenstein Monster have explained the issue well, but I haven't found an authoritative citation yet.
#35
06-15-2018, 05:02 PM
 Guest Join Date: Aug 1999 Location: Alabama Posts: 16,441
This is an N-body problem (or 3-body if you just consider Sun, Earth and Jupiter). It doesn't follow Kepler's laws. You can't reduce it into a 2-body problem by replacing 2 objects with 1 at their barycenter.

Last edited by scr4; 06-15-2018 at 05:03 PM.
#36
06-16-2018, 08:42 AM
 Guest Join Date: Nov 2009 Location: Eugene, Oregon Posts: 1,350
Let's simplify the problem and imagine just three bodies: the Sun, Earth, and Jupiter. Would it be fair to say that the Sun and Earth both orbit the Sun-Earth barycenter but Jupiter and the Sun-Earth system orbit the Sun-Earth-Jupiter barycenter? If that's the case, then it seems logical to me that Earth actually orbits the Sun-Mercury-Venus-Earth-Luna barycenter whereas Jupiter orbits the Sun-Mercury-Venus-Earth-Luna-Mars-Asteroids-Jupiter barycenter. But all the sources I've found say that Earth and Jupiter both orbit the solar system barycenter.

Can anyone find some actual emperical data on measuring the Earth-Sun distance to an accuracy level which could detect deviations away from the numbers predicted by the Earth-Sun elipse, caused by the position of Jupiter (if such deviation exists)? If the emperical data shows no deviation, that would support the claim that Jupiter doesn't affect the Earth-Sun distance.
#37
06-16-2018, 08:55 AM
 Member Join Date: Oct 2000 Posts: 7,263
Quote:
 Originally Posted by sbunny8 Let's simplify the problem and imagine just three bodies: the Sun, Earth, and Jupiter. Would it be fair to say that the Sun and Earth both orbit the Sun-Earth barycenter but Jupiter and the Sun-Earth system orbit the Sun-Earth-Jupiter barycenter? If that's the case, then it seems logical to me that Earth actually orbits the Sun-Mercury-Venus-Earth-Luna barycenter whereas Jupiter orbits the Sun-Mercury-Venus-Earth-Luna-Mars-Asteroids-Jupiter barycenter. But all the sources I've found say that Earth and Jupiter both orbit the solar system barycenter. Can anyone find some actual emperical data on measuring the Earth-Sun distance to an accuracy level which could detect deviations away from the numbers predicted by the Earth-Sun elipse, caused by the position of Jupiter (if such deviation exists)? If the emperical data shows no deviation, that would support the claim that Jupiter doesn't affect the Earth-Sun distance.
That's a great idea, and finally led me to a good citation. Here's a chart of the perihelion and aphelion dates, times and distances for a hundred year period http://www.astropixels.com/ephemeris/perap2001.html. The variability of perihelion and aphelion distances is a few thousand kilometers, not hundreds of thousands of kilometers even though sometimes perihelion occurs when Jupiter is on one side of the Sun (relative to Earth) and sometimes on the other side.

Last edited by Andy L; 06-16-2018 at 08:56 AM.
#38
06-16-2018, 10:02 AM
 Guest Join Date: Dec 2009 Location: State of Jefferson Posts: 8,499
Quote:
 Originally Posted by Chronos Stand on the surface of the Moon, right in the middle of the Earth-facing side. The Earth-Moon barycenter will be directly above you. The Moon will be directly below you. If you let go of something, which way does it fall, towards the barycenter or towards the Moon? The net force vectors don't all point to the barycenter. I can't explain why they don't, because there's no reason why they would. Individual components of the net force point towards individual objects, and then you add up all of those components to get the net force.
This pen in front of me is on the Moon's side of the Earth/Moon barycenter, I let it go it falls towards Earth because the gravity force is so much stronger ... maybe I'm thinking barycenter means something else ... because it's just a point in space, not "treating it as a point", but in fact, it is a point ... no mass, no gravity, no nothing ... there's no reason for the net force vector to point at the barycenter except that this net force vector has to point someplace, and if not the barycenter, then where? ...

I've given too much thought to this, so please excuse my repeating what sbunny posted above ... I'm wording this a little different, but the question is the same ... we're at the Sun and we experience a gravity force vector pointed towards the Earth AND a second force vector pointed towards the Moon ... now the Sun can only have one acceleration vector, so we ADD the two gravity force vectors to get a resultant force vector and use this to calculate our acceleration vector ... this resultant vector points towards the barycenter at all times ...

You seem to be claiming that the Earth is following the ellipse and I'm claiming the Earth has 13 distinct wobbles per year in and out of this ellipse ... I haven't bothered with a citation thinking the Wikipedia article "Perturbation" is good enough for this hijack ... noting that I agree 100% none of this is relevant to the effects of Jupiter on the Earth's climate short of a billion year time interval, and even at this long period the effect may well be within instrumentation error ...

Quote:
 Originally Posted by scr4 This is an N-body problem (or 3-body if you just consider Sun, Earth and Jupiter). It doesn't follow Kepler's laws. You can't reduce it into a 2-body problem by replacing 2 objects with 1 at their barycenter.
Please note your reference here clearly states "(although in reality neither of the bodies are truly stationary, as they both orbit the center of mass of the whole system—about the barycenter)" ... this seems to support what sbunny is claiming ...

ETA: From Andy L's citation: "Due of the gravitational perturbation of the Moon (and to a much lesser extent the planets), Earth's actual distance at perihelion can vary from 0.9831914 AU (147,083,346 km) to 0.9833860 AU (147,112,452 km). This is a range of 0.0001946 AU (29,106 km), which corresponds to about 2.28 times the 12,756 km equatorial diameter of Earth."

Last edited by watchwolf49; 06-16-2018 at 10:04 AM.
#39
06-16-2018, 10:58 AM
 Guest Join Date: Sep 2001 Location: Chicago, IL Posts: 23,570
Quote:
 Originally Posted by sbunny8 Let's simplify the problem and imagine just three bodies ...
You really think a three body problem is simplifying things? Even I (admittedly more form the book of the same name than any formal education that included it) know how difficult a three body problem is.

Question from an ignorant one here: it would seem to me that the barycenter is everchanging, which is part of what makes it so complicated. Is that an incorrect understanding?
#40
06-16-2018, 11:52 AM
 Guest Join Date: Aug 1999 Location: Alabama Posts: 16,441
Quote:
 Originally Posted by watchwolf49 Please note your reference here clearly states "(although in reality neither of the bodies are truly stationary, as they both orbit the center of mass of the whole system—about the barycenter)" ... this seems to support what sbunny is claiming ...
No, this is just saying the TWO bodies orbit around each other's barycenter. Even when we approximate the 3-body problem by assuming that the 3rd body is too small to affect the other two, the third body follows a path that isn't quite circular or elliptical. If it's very close to one body, it will be very close to a circular orbit around that body. E.g. the Apollo spacecraft started out in a nearly circular orbit around the earth, and ended up in a nearly circular orbit around the Moon.

Last edited by scr4; 06-16-2018 at 11:55 AM.
#41
06-16-2018, 11:57 AM
 Guest Join Date: May 2016 Posts: 4,730
Quote:
 Originally Posted by DSeid Question from an ignorant one here: it would seem to me that the barycenter is everchanging, which is part of what makes it so complicated. Is that an incorrect understanding?
If a system of particles, like the Solar System, is acted on by an external force, then the centre of mass will move as a result of that force. If there is no external force, then the acceleration of the centre of mass will be zero.
#42
06-16-2018, 01:02 PM
 Guest Join Date: May 2016 Posts: 4,730
I wrote in the other thread that the Sun "orbits" the solar-system barycenter, but, of course, the complicated motion influenced by Jupiter, Saturn, Neptune, and the rest is hardly a Keplerian orbit, in case that was in question.
#43
06-16-2018, 03:01 PM
 Charter Member Join Date: Mar 2001 Location: San Jose Posts: 43,831
To get back to the Op. Sure Jupiter may effect the Earths temp a tiny bit.

But usually these factoids, like with sunspots, are trying to show that Human caused global warming is false.

Nothing, other than human emitted CO2, etc- can account for the rise which is mapped against human caused CO2 etc release.

That rise- which is small and slow (when measured vs human span) is surely caused by humans and is what is concerning scientists- because altho we see it as "slow" it is really fast on a geologic time scale.
#44
06-16-2018, 03:31 PM
 Member Join Date: Oct 2000 Posts: 7,263

"About the sun thus librated the other planets are revolved in elliptic orbits (p 403), and, by radii drawn to the sun, describe areas nearly proportional to the times, as is explained in Prop. LXV. If the sun was quiescent, and the other planets did not act mutually one upon another, their orbits would be elliptic, and the areas exactly proportional to the times (by Prop. XI, and Cor. 1, Prop. XIII). But the actions of the planets among themselves, compared with the actions of the sun on the planets, are of no moment, and produce no sensible errors. And those errors are less in revolutions about the sun agitated in the manner but now described than if those revolutions were made about the sun quiescent (by Prop. LXVI, and Cor. Prop. LXVIII), especially if the focus of every orbit is placed in the common centre of gravity of all the lower included planets; viz., the focus of the orbit of Mercury in the centre of the sun; the focus of the orbit of Venus in the common centre of gravity of Mercury and the sun; the focus of the orbit of the earth in the common centre of gravity of Venus, Mercury, and the sun; and so of the rest. And by this means the foci of the orbits of all the planets, except Saturn, will not be sensibly removed from the centre of the sun, nor will the focus of the orbit of Saturn recede sensibly from the common centre of gravity of Jupiter and the sun"

I summarize this as "The deviations in orbits due to the interaction between the planets (the gravity of Earth on Venus, etc.) are tiny; a bigger effect is the fact that the focus of planet A's orbit is the center of mass of Sun and all the planets inside the orbit of planet A. Since the center of mass of the Sun and all the planets inside Jupiter is essentially the center of mass of the Sun (since all the inner planets are tiny compared to the Sun), only for Saturn do we have to worry about the effect of Jupiter.
#45
06-16-2018, 03:59 PM
 Guest Join Date: Dec 2009 Location: State of Jefferson Posts: 8,499
Note that Newton passed away a little over 50 years prior to the discovery of Uranus ...

Last edited by watchwolf49; 06-16-2018 at 03:59 PM.
#46
06-16-2018, 04:34 PM
 Member Join Date: Oct 2000 Posts: 7,263
Quote:
 Originally Posted by watchwolf49 Note that Newton passed away a little over 50 years prior to the discovery of Uranus ...
I should have mentioned that, yes.
#47
03-24-2020, 02:32 PM
 Member Join Date: Oct 2000 Posts: 7,263
A paper published last year had the same misconception about Jupiter's effect on the sun - and that paper was retracted a couple of weeks ago https://www.msn.com/en-us/news/techn...al/ar-BB10OaJy
#48
03-24-2020, 02:53 PM
 Guest Join Date: Jan 2001 Posts: 27,970
Quote:
 Originally Posted by Grrr! So that must mean, when Jupiter is in alignment with Earth, the sun is now 500-thousand miles closer to it. That seems like a lot! Certainly enough to cause significant change. Am I missing something here?
It's a lot if you don't have a diameter of 860,000 miles, shining on a tiny ball 92 million miles away.
#49
03-24-2020, 06:53 PM
 Charter Member Moderator Join Date: Jan 2000 Location: The Land of Cleves Posts: 87,266
Well, Newton was prior to the known discovery of Uranus, at least. Galileo made a few observations of it, but didn't realize at the time that that's what he was observing. Under ideal conditions, it can even be seen by the naked eye.
#50
03-24-2020, 07:01 PM
 Member Join Date: Jan 2004 Posts: 13,004
I'm not an astrophysicist or a rocket surgeon, but even I can see that a paper that says the distance varies by 1.85 million miles is inconsequential to the 91 - 94 millions miles the distance usually varies.

People don't review these papers before they get published?

 Bookmarks

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is Off HTML code is Off Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Main     About This Message Board     Comments on Cecil's Columns/Staff Reports     The Quarantine Zone     General Questions     Great Debates     Politics & Elections     Cafe Society     The Game Room     Thread Games     In My Humble Opinion (IMHO)     Mundane Pointless Stuff I Must Share (MPSIMS)     Marketplace     The BBQ Pit

All times are GMT -5. The time now is 01:52 AM.

 -- Straight Dope v3.7.3 -- Sultantheme's Responsive vB3-blue Contact Us - Straight Dope Homepage - Archive - Top

Send questions for Cecil Adams to: cecil@straightdope.com