If the Moon were replaced by other planets...
- Thread starter Gary7
- Start date
I was half expecting the Sun to suddenly pop up at the end and engulf everything.
At the beginning of the clip the Earth's moon is a pretty small spot. They should have left it somewhere in the frame so your eyes would have a comparative reference point.
Some of it might be down to perspective. Sometimes bodies such as the Sun and the Moon can appear larger or smaller than they actually are depedning on what else you are looking at.
Remember the Sun is something like 400x the diameter of the moon, they only look the same size because the sun is 400x further away from the Earth thn the moon.
Remember the Sun is something like 400x the diameter of the moon, they only look the same size because the sun is 400x further away from the Earth thn the moon.
1. Download Celestia, install and launch.
2. RETURN. "Moon" RETURN. G.
3. Note the distance in the info display at upper left. Now use HOME and END to set your distance at 400,000 km, roughly the apogee of the Moon from Earth. (The default FOV is noted at lower right. You can change that if you wish, but the default view will do for this exercise.)
4. Now go to Jupiter: 5. G.
5. Again, set your distance to (approximately) 400,000 km. A super of the two images looks like this:
(I have orbits turned on, which is what those lines are.)
2. RETURN. "Moon" RETURN. G.
3. Note the distance in the info display at upper left. Now use HOME and END to set your distance at 400,000 km, roughly the apogee of the Moon from Earth. (The default FOV is noted at lower right. You can change that if you wish, but the default view will do for this exercise.)
4. Now go to Jupiter: 5. G.
5. Again, set your distance to (approximately) 400,000 km. A super of the two images looks like this:
(I have orbits turned on, which is what those lines are.)
Well, yeah, but in this case the whole point is that Jupiter and Saturn are supposedly the exact same distance as the moon. According to the scale presented here, I'm way less impressed with how big those planets are.
Though part of me does wonder if the time of year and the sky might have played a role. The moon was presented as being quite tiny, yet there are definitely days throughout the year when the moon looks HUGE because of the way the light is bouncing around in the atmosphere.
Jupiter's radius Rj is about 10.9 times the Earth's radius Re, which is about 3.7 time's the Moon's radius Rm, so the angle subtended at the same distance would be about 40 times greater for Jupiter than the Moon and the solid angle (apparent area subtended) would be about 1600 times greater.
Jupiter is 88,736 miles in diameter and the moon is 2,160 miles in diameter, so the area difference is 1,688. The albedo of the moon is 0.12 and Jupiter is 0.52, so the nighttime full moon brightness would go up by 7,313. Bright moonlight is about 0.25 Lux (0.2 to 0.3), so with Jupiter we could have 1,800 Lux. Office lighting is usually 300 to 500 Lux and a TV studio is about 1,000 Lux, as is an overcast day. So it would be very bright indeed.
I'd hate to think what all that would do to our oceans. Though we'd be the moon rather than have a moon there.
I wouldn't worry too much about the oceans. The tidal effects of even a much closer moon would tear the crust apart.
At a distance of 1 AU from the Sun, agreed. At the distance of Jupiter, about 5.2 AU, the luminous flux would be about 27 times less than that -- 67 lux. Bright sunlight on Earth at 1 AU is about 120,000 lux.
Not disagreeing. I'm being didactic, possible too much so...
Admittedly it would be easier to move the Earth to Jupiter than vice versa, but if the Earth was out at Jupiter's distance it would be too cold to stand outside making videos.
However it does bring up the not unlikely possibility that in many of the solar systems where we've detected Jupiter size planets orbiting close in (because they're easy to detect), there could be Earth-size moons around the gas giants that would could be perfect for life. The people who live on them no doubt comment on what their sky would look like if they had a regular moon like normal people.
However it does bring up the not unlikely possibility that in many of the solar systems where we've detected Jupiter size planets orbiting close in (because they're easy to detect), there could be Earth-size moons around the gas giants that would could be perfect for life. The people who live on them no doubt comment on what their sky would look like if they had a regular moon like normal people.
At 384,000 km, I think the Earth would be within the orbit of Io, which interacts significantly with Jupiter's magnetosphere. It'd be outside the main radiation belts at 100,000 to 140,000 km though. Spacecraft tend to avoid going closer to Jupiter than 300,000 km.
I don't think the person who created the video tried to be accurate on planetary dimensions versus distance, but rather sought out what would look visually appealing. And it's just about proximity, of course... as anything larger than the Earth would in turn make the Earth its moon. 
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