# If Jupiter was the moon...

divegeester
Science 28 Jun '18 12:42
1. divegeester
the altruistic one
28 Jun '18 12:42
Other than us being is serious harms way...

Would it (pretty much) fill the sky from horizon to horizon?

I am guessing it would fill the width of a meter rule held at arms length.

Any better, more mathematical, guesses?
2. DeepThought
28 Jun '18 13:04
Originally posted by @divegeester
Other than us being is serious harms way...

Would it (pretty much) fill the sky from horizon to horizon?

I am guessing it would fill the width of a meter rule held at arms length.

Any better, more mathematical, guesses?
The earth would be the moon and jupiter the planet. How big it would be in the sky depends on the radius of the orbit. It's a fairly simple trigonometry problem.
3. sonhouse
Fast and Curious
28 Jun '18 17:32
Originally posted by @deepthought
The earth would be the moon and jupiter the planet. How big it would be in the sky depends on the radius of the orbit. It's a fairly simple trigonometry problem.
It doesn't even need trig. If it was at the distance to Luna, say 300,000 km for grins, then the orbit would be about 2 million km around and Jove is about 130,000 km wide that takes up about 1/15th of the circle represented by that orbit. It would subtend roughtly 24 degrees across the sky, about 1/8th of the sky from horizon to horizon.
4. DeepThought
28 Jun '18 19:12
Originally posted by @sonhouse
It doesn't even need trig. If it was at the distance to Luna, say 300,000 km for grins, then the orbit would be about 2 million km around and Jove is about 130,000 km wide that takes up about 1/15th of the circle represented by that orbit. It would subtend roughtly 24 degrees across the sky, about 1/8th of the sky from horizon to horizon.
That was trigonometry. I was wondering about putting bounds on it, since there'll be a closest orbit, where the Earth won't be pulled apart by tidal forces, and a furthest one, where the Earth is still bound. I suspect the distance you've used might be inside the Roche limit (if I've remembered the right term).
5. divegeester
the altruistic one
28 Jun '18 21:01
Originally posted by @sonhouse
It doesn't even need trig. If it was at the distance to Luna, say 300,000 km for grins, then the orbit would be about 2 million km around and Jove is about 130,000 km wide that takes up about 1/15th of the circle represented by that orbit. It would subtend roughtly 24 degrees across the sky, about 1/8th of the sky from horizon to horizon.
That sounds like about one metre, as per a metre rule held at arms length?
6. sonhouse
Fast and Curious
28 Jun '18 21:101 edit
Originally posted by @divegeester
That sounds like about one metre, as per a metre rule held at arms length?
I think it would be something like that, give or take.

Roche limit would make things difficult for Earth even if we were not at the limit, the amount of tides would be maybe 10 times what they are now or more.

Deep, here is a link to Roche limit formulae,

https://en.wikipedia.org/wiki/Roche_limit

My question is the units, what are they, I know they are MKS I think but I get nonsense answers when I plug in numbers.

Mass of Jove, ~1.9E27 Kg, radius ~64,000 km, density ~1.3 Gm/Cm^3 but they seem to using numbers for that 1000 X higher.

Earth/Moon distance, ~ 384,000 km, Earth mass ~ 6E24 Kg, density 5.5 gm/cm^3

https://en.wikipedia.org/wiki/Roche_limit

There is a simplified formula D=~1.26 R (DM/dm)^.3333 (cube root)

It sure would be nice to put in units for us without Phd's in physics.
7. divegeester
the altruistic one
28 Jun '18 21:141 edit
Originally posted by @sonhouse
I think it would be something like that, give or take.

Roche limit would make things difficult for Earth even if we were not at the limit, the amount of tides would be maybe 10 times what they are now.
I just did a guess based on the relative sizes of the moon and Jupiter. That would be a pretty impressive sight in the sky both by day and especially at night.
8. sonhouse
Fast and Curious
28 Jun '18 21:48
Originally posted by @divegeester
I just did a guess based on the relative sizes of the moon and Jupiter. That would be a pretty impressive sight in the sky both by day and especially at night.
Yeah but like DT said, Jupiter at Luna distance may destroy Earth where the Roche limit is where tidal forces = gravitational attraction where loose objects would float off the planet and such.

I found the formulas for that but can't figure out the units so I get nonsense numbers doing the arithmetic.
9. divegeester
the altruistic one
29 Jun '18 04:04
Originally posted by @sonhouse
Yeah but like DT said, Jupiter at Luna distance may destroy Earth where the Roche limit is where tidal forces = gravitational attraction where loose objects would float off the planet and such.

I found the formulas for that but can't figure out the units so I get nonsense numbers doing the arithmetic.
“May destroy”?? I think it would most certainly be game over on planet Earth.

But I’m just thinking about the hypothetical visual impact of something that large being that close, albeit still at 250,000 miles.
10. sonhouse
Fast and Curious
29 Jun '18 12:341 edit
Originally posted by @divegeester
“May destroy”?? I think it would most certainly be game over on planet Earth.

But I’m just thinking about the hypothetical visual impact of something that large being that close, albeit still at 250,000 miles.
Not sure about that, the moon closest to Jupiter is only 120,000 odd km away from Jove. It's about 30 km across, 80,000 miles away in stupid units and 20 miles across.
And that moon survives quite well. But of course Earth is many times larger and more massive so not totally sure.
11. Ponderable
chemist
03 Jul '18 10:351 edit
Originally posted by @divegeester
Other than us being is serious harms way...

Would it (pretty much) fill the sky from horizon to horizon?

I am guessing it would fill the width of a meter rule held at arms length.

Any better, more mathematical, guesses?
using the Intercept Theorem which is part of elementary geometry you find that a length A at a distance of B is directly proportinal to an (unknown) length C at a distance D with B/D=C/D

Since you agve us 1 m at arms length (say 0.8 m) and the Diameter of Jupiter (143.000 km). The distance would be 114 000 km, which would be much nearer than the moon is...
12. sonhouse
Fast and Curious
03 Jul '18 15:29
Originally posted by @ponderable
using the Intercept Theorem which is part of elementary geometry you find that a length A at a distance of B is directly proportinal to an (unknown) length C at a distance D with B/D=C/D

Since you agve us 1 m at arms length (say 0.8 m) and the Diameter of Jupiter (143.000 km). The distance would be 114 000 km, which would be much nearer than the moon is...
How does that relate to the Roche limit? What angle would Jove subtend at that 114K ?
13. Ponderable
chemist
04 Jul '18 11:02
Originally posted by @sonhouse
How does that relate to the Roche limit? What angle would Jove subtend at that 114K ?
If we consider the densities of Jupiter with 1,33 and the density of the earth with 5,15 we end up with R*0.8 that is Jupiter would strip the earth of all gaseous material (atmosphere and water) but the rest would be stable.

I can't say that I understood the other question...
14. Ponderable
chemist
04 Jul '18 13:37
Probably the earth would be pulled into Jupiter quite fast anyway
15. sonhouse
Fast and Curious
04 Jul '18 16:56
Originally posted by @ponderable
If we consider the densities of Jupiter with 1,33 and the density of the earth with 5,15 we end up with R*0.8 that is Jupiter would strip the earth of all gaseous material (atmosphere and water) but the rest would be stable.

I can't say that I understood the other question...
Just how big would Jupiter appear in the sky at that distance, what 110Km? I can do that one, no big deal. Well that seems to be an interesting number, Jove would be one radian wide, 57 odd degrees in Earth's sky.

If the orbital velocity was right Earth would just orbit Jove just like the ISS orbits Earth and with little in the way of atmosphere it would stay that way for a billion years.