# If Jupiter were the same distance as the Moon. **URL:** \ **Category:** Factual Questions\ **Created:** [April 9, 2013, 4:41am UTC](https://boards.straightdope.com/t/if-jupiter-were-the-same-distance-as-the-moon/655206 "2013-04-09T04:41:30Z")\ **Posts on this page:** 18\ **Page:** 2
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [April 9, 2013, 3:04pm UTC](https://boards.straightdope.com/t/if-jupiter-were-the-same-distance-as-the-moon/655206/21 "2013-04-09T15:04:28Z")
> [@lazybratsche](#): > > If the Earth was tidally locked, the solar eclipse would only occur for the side of the Earth that’s facing Jupiter. That would probably make that side substantially colder and subject to rather chaotic weather patterns. On the other hand, the Jupiter-facing side receives reflected light from Jupiter all night, and some infrared radiation all the time. I suspect this will make up for the eclipses and make that side as warm as the far side. Another thing - if you lived on the Jupiter side of the Earth, you will _never see stars_. At sunset you have a half-full Jupiter in the sky, which waxes to full (at least 1000 times brighter than the full moon) before waning to half at sunrise. At no point do you get a dark sky. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [April 9, 2013, 4:44pm UTC](https://boards.straightdope.com/t/if-jupiter-were-the-same-distance-as-the-moon/655206/22 "2013-04-09T16:44:39Z")
First off, I’m impressed that the day/night line on Jupiter and the shadows plausibly agree with each other in that picture. I might have rotated Jupiter a little bit CCW, but I can’t be sure that would be more accurate. Looks pretty close, anyway. For the effect of Jupiter on the Earth’s temperature, I did a little math. Jupiter’s radius is R = 69,911 km, and the Moon’s orbital radius is about L = 384,300 km, for a ratio of R/L = 0.182. Assuming the Earth’s orbit is in the plane of Jupiter’s orbit, the fraction of the Earth’s orbit eclipsed by Jupiter is 2_R / 2_pi\*L = 0.0579, so about 5.8 percent less solar radiation. Jupiter essentially reradiates all the energy it receives from the Sun. It’s cross-section for capturing solar energy is pi_R^2, and that will be spread over 4_pi_L^2 when the Earth receives it, so the additional energy received will be pi_R^2/(4_pi_L^2) = 0.0083 as much as is received directly from the Sun, or about 0.8 percent. The total difference in energy received by the Earth is then the difference in those numbers, or about 5 percent smaller than received now. I’ll let someone else figure out if receiving more IR and maybe optical, and less UV, makes a difference. The far side of the Earth will receive about the same amount of energy, since it’s night there during the eclipses, so that means the near side is receiving about 10 percent less energy. > [@scr4](#): > > Another thing - if you lived on the Jupiter side of the Earth, you will never see stars. At sunset you have a half-full Jupiter in the sky, which waxes to full (at least 1000 times brighter than the full moon) before waning to half at sunrise. At no point do you get a dark sky. Well, except during those eclipses. ---
**Author:** ![Earl\_Snake-Hips\_Tucker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/earl_snake-hips_tucker/32/3269_2.png) [@Earl\_Snake-Hips\_Tucker](https://boards.straightdope.com/u/Earl_Snake-Hips_Tucker)\ **Post date:** [April 9, 2013, 5:25pm UTC](https://boards.straightdope.com/t/if-jupiter-were-the-same-distance-as-the-moon/655206/23 "2013-04-09T17:25:42Z")
[QUOTE=standingwave;16176654. . .[ICRP] ([International Commission on Radiological Protection - Wikipedia](http://en.wikipedia.org/wiki/International_Commission_on_Radiological_Protection)) recommends limiting artificial irradiation of the public to an average of 100 mrem (1 mSv) of effective dose per year. Io receives about 3,600 rem (36 Sv) of radiation per day. So there’s that. [/QUOTE] Eh. . . So carry a parsol. ---
**Author:** ![Jman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jman/32/4416_2.png) [@Jman](https://boards.straightdope.com/u/Jman)\ **Post date:** [April 9, 2013, 5:34pm UTC](https://boards.straightdope.com/t/if-jupiter-were-the-same-distance-as-the-moon/655206/24 "2013-04-09T17:34:00Z")
And again, IF there are eclipses, which is not guaranteed, depending on the angle of inclination of the orbit of earth around Jupiter. From a quick CAD experiment, it looks like an orbit inclination of about 11.5 degrees would make eclipses a much rarer event. Below that, and eclipses would happen ‘daily’ (which in this case would be each orbit of Earth around Jupiter). When eclipses WOULD happen, they would only last for about 6% of the ‘day’, assuming the Earth is in alignment such that the eclipse occurs across the entire diameter of Jupiter, rather than a more oblique part (depending on orbit inclination). Someone may have to correct me, but I believe I did the calculation right for the orbital period of earth at that distance to Jupiter, and it’s fast - about 37 hours, so even an eclipse with the earth exactly in the plane of Jupiter’s orbit would only last about 2.2 hours per day. The heat loss is shown above by ZenBeam. ---
**Author:** ![Czarcasm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/czarcasm/32/4050_2.png) [@Czarcasm](https://boards.straightdope.com/u/Czarcasm)\ **Post date:** [April 9, 2013, 5:40pm UTC](https://boards.straightdope.com/t/if-jupiter-were-the-same-distance-as-the-moon/655206/25 "2013-04-09T17:40:46Z")
Throwing tides back into the equation, what(if any) would be the difference in tidal action on Earth between us orbiting Jupiter and Jupiter orbiting us? ---
**Author:** ![Elendil\_s\_Heir](https://avatars.discourse-cdn.com/v4/letter/e/7cd45c/32.png) [@Elendil\_s\_Heir](https://boards.straightdope.com/u/Elendil_s_Heir)\ **Post date:** [April 9, 2013, 5:44pm UTC](https://boards.straightdope.com/t/if-jupiter-were-the-same-distance-as-the-moon/655206/26 "2013-04-09T17:44:47Z")
Cool discussion. These might also be of interest: > **[Real science Q? about an Arthur C. Clarke plot point](https://boards.straightdope.com/sdmb/showthread.php?t=160176)** > > In 2010 The Odyssey Two, the monoliths turn Jupiter into another star. How? I assume the monoliths had to change the mass of Jupiter, because it wouldn’t be able to sustain fusion at it’s current mass. Is this a valid assumption? How much mass would... [http://www.physics.uci.edu/~observat/Physical\_Scales.html](http://www.physics.uci.edu/~observat/Physical_Scales.html) (keep scrolling down for the supergiant stars) ---
**Author:** ![AndrewL](https://avatars.discourse-cdn.com/v4/letter/a/3d9bf3/32.png) [@AndrewL](https://boards.straightdope.com/u/AndrewL)\ **Post date:** [April 9, 2013, 6:55pm UTC](https://boards.straightdope.com/t/if-jupiter-were-the-same-distance-as-the-moon/655206/27 "2013-04-09T18:55:20Z")
> [@UDS](#): > > However if, instead of moving the Earth to Jupiter’s current location, we move Jupiter to the Earth’s, presumably Jupiter’s orbital period in that location would be much smaller than Earth’s, given its much greater mass. Actually, no. The mass of a planet has little to no effect on the time it takes to orbit. If you moved Jupiter into Earth’s orbit, Jupiter would take 1 year to orbit the sun. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [April 9, 2013, 7:11pm UTC](https://boards.straightdope.com/t/if-jupiter-were-the-same-distance-as-the-moon/655206/28 "2013-04-09T19:11:56Z")
Is this with Jupiter’s centre at the same distance as the Moon’s centre, or the minimum surface to surface distance being the same? (because with something as big as Jupiter, it makes a lot of difference) ---
**Author:** ![MonkeyMensch](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@MonkeyMensch](https://boards.straightdope.com/u/MonkeyMensch)\ **Post date:** [April 9, 2013, 8:28pm UTC](https://boards.straightdope.com/t/if-jupiter-were-the-same-distance-as-the-moon/655206/29 "2013-04-09T20:28:12Z")
> [@Mangetout](#): > > Is this with Jupiter’s centre at the same distance as the Moon’s centre, or the minimum surface to surface distance being the same? (because with something as big as Jupiter, it makes a lot of difference) Well, it would make a 17% difference. Does that qualify as a \*\*lot \*\*of difference? The rest of this post assumes a co-planar orbital alignment. There are a couple of other points only obliquely referred to, so far: [ul] [li]Those observers on the Jovian facing hemisphere would see The Big Fat One change phases at the rate of about 10 degrees per hour. It wouldn’t quite noticeable when gazing at it, but certainly twenty or thirty minutes difference in viewing times would see a noticeable difference. All in all, it would be pretty impressive.[/li][/ul] [ul] [li] Just as the “daily” solar eclipse would last about two hours, so would the Earth’s shadow track across the face of The Big Fat One in around the same time. And no puny dot of shadow would that be! I figure the Earth’s shadow might be about 6,000 miles across at that distance. To get a feel for its appearance that’s around 70% of the North-South dimension of the Great Red Spot.[/li][/ul] You have to believe that astronomy would advance more quickly with such nearby examples of revolution. Or maybe not, what with those religious nuts on either side of the Earth. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [April 9, 2013, 8:42pm UTC](https://boards.straightdope.com/t/if-jupiter-were-the-same-distance-as-the-moon/655206/30 "2013-04-09T20:42:31Z")
> [@MonkeyMensch](#): > > Well, it would make a 17% difference. Does that qualify as a \*\*lot \*\*of difference? 17% of Jupiter is a lot, so… yes, I think. ---
**Author:** ![standingwave](https://avatars.discourse-cdn.com/v4/letter/s/9de0a6/32.png) [@standingwave](https://boards.straightdope.com/u/standingwave)\ **Post date:** [April 9, 2013, 8:47pm UTC](https://boards.straightdope.com/t/if-jupiter-were-the-same-distance-as-the-moon/655206/31 "2013-04-09T20:47:13Z")
[quote=“MonkeyMensch, post:29, topic:655206”] [ul] [li] Just as the “daily” solar eclipse would last about two hours, so would the Earth’s shadow track across the face of The Big Fat One in around the same time. And no puny dot of shadow would that be! I figure the Earth’s shadow might be about 6,000 miles across at that distance. To get a feel for its appearance that’s around 70% of the North-South dimension of the Great Red Spot.[/li][/quote] [/ul] [This image](http://www.mreclipse.com/LEphoto/TLE2000Jan/image/TLE2000umbra2w.JPG) gives an idea of the size of the Earth’s shadow (umbra) at that distance. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [April 9, 2013, 9:27pm UTC](https://boards.straightdope.com/t/if-jupiter-were-the-same-distance-as-the-moon/655206/32 "2013-04-09T21:27:16Z")
> [@Czarcasm](#): > > Throwing tides back into the equation, what(if any) would be the difference in tidal action on Earth between us orbiting Jupiter and Jupiter orbiting us? I’m not sure how to approach this. For Jupiter to be orbiting Earth, Jupiter would have to be significantly less massive than Earth. So either Earth isn’t really Earth any more, or Jupiter isn’t really Jupiter any more. ---
**Author:** ![Ludovic](https://avatars.discourse-cdn.com/v4/letter/l/7ab992/32.png) [@Ludovic](https://boards.straightdope.com/u/Ludovic)\ **Post date:** [April 9, 2013, 9:29pm UTC](https://boards.straightdope.com/t/if-jupiter-were-the-same-distance-as-the-moon/655206/33 "2013-04-09T21:29:19Z")
Even if we were tidally locked, we’d still have tides from the Sun. ---
**Author:** ![standingwave](https://avatars.discourse-cdn.com/v4/letter/s/9de0a6/32.png) [@standingwave](https://boards.straightdope.com/u/standingwave)\ **Post date:** [April 9, 2013, 10:07pm UTC](https://boards.straightdope.com/t/if-jupiter-were-the-same-distance-as-the-moon/655206/34 "2013-04-09T22:07:16Z")
> [@ZenBeam](#): > > I’m not sure how to approach this. For Jupiter to be orbiting Earth, Jupiter would have to be significantly less massive than Earth. So either Earth isn’t really Earth any more, or Jupiter isn’t really Jupiter any more. Yeah. Technically, no body truly orbits another. Even in a simple two body system, the bodies orbit around a common center of gravity. In this example, the barycenter would be within Jupiter itself, but not at its center. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [April 9, 2013, 10:44pm UTC](https://boards.straightdope.com/t/if-jupiter-were-the-same-distance-as-the-moon/655206/35 "2013-04-09T22:44:29Z")
How about this: We keep the semi-major axis of the Earth’s orbit the same as the Moon, but we put it into a [spin-orbit resonance](http://en.wikipedia.org/wiki/Mercury_(planet)#Spin.E2.80.93orbit_resonance) like Mercury. Then the day will be close to a current Earth day, everyone gets to see Jupiter, everyone gets to see stars, everyone gets to see eclipses, and there isn’t one side that’s colder than the other. Any downsides? Too much seismic heating? ---
**Author:** ![Recusant](https://avatars.discourse-cdn.com/v4/letter/r/838e76/32.png) [@Recusant](https://boards.straightdope.com/u/Recusant)\ **Post date:** [April 9, 2013, 10:57pm UTC](https://boards.straightdope.com/t/if-jupiter-were-the-same-distance-as-the-moon/655206/36 "2013-04-09T22:57:25Z")
Not quite what you’re asking (I don’t have nearly the knowledge of astrophysics for that), but if the topic interests you, you might want to check out two books by Neil F. Comins entitled “What if the Moon didn’t exist?” and “What if the Earth had two moons?”. Both interesting reads. ---
**Author:** ![chorpler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chorpler/32/2888_2.png) [@chorpler](https://boards.straightdope.com/u/chorpler)\ **Post date:** [April 10, 2013, 12:02am UTC](https://boards.straightdope.com/t/if-jupiter-were-the-same-distance-as-the-moon/655206/37 "2013-04-10T00:02:12Z")
Speaking of the religious aspect of this kind of thing … Robert J. Sawyer’s _Quintaglio Ascension_ trilogy starts out with the book **Far-Seer** , where the protagonist, a member of an intelligent race of dwarf tyrannosaurs who live on the innermost moon of a gas giant, deals with this – the whole plot involves the protagonist’s pilgrimage to see the recently-discovered “Face of God” (which is of course the gas giant they orbit) by sailing around to the other side of the world from their single continent. I enjoyed it… ---
**Author:** ![John\_DiFool](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_difool/32/19543_2.png) [@John\_DiFool](https://boards.straightdope.com/u/John_DiFool)\ **Post date:** [April 10, 2013, 1:05am UTC](https://boards.straightdope.com/t/if-jupiter-were-the-same-distance-as-the-moon/655206/38 "2013-04-10T01:05:05Z")
More mythology musings…I’d imagine their initial cosmology would be Jupitercentric. How long before people would properly identify that black spot on Jupiter as the shadow of their own world (the far siders in that case). Which side would develop more quickly, culturally & scientifically? I’d guess the far siders (checking out said trilogy). [Previous page](https://boards.straightdope.com/t/if-jupiter-were-the-same-distance-as-the-moon/655206.md?page=1)