### If Jupiter was placed in Mars' orbit, how would Jupiter appear from the naked eye?

• If Jupiter were as far from us as Mars, how big would it appear in Earth's sky? Would it appear huge, or would it be as small as a star?

The rewording of this question makes it a purely hypothetical. I'm voting to close this question as off-topic because purely hypothetical questions are off topic for this stack exchange. The previous version (How big does Jupiter appear from Mars) would be acceptable.

Wow that really does change the question and answer a lot... but the same math applies, from below, just change the numbers accordingly. If you do that you'll find the size quite surprising!

• If we were to view Jupiter from Mars's orbit with the the naked eye, how big would it appear to be, as compared with its appearance from the Earth? Would Jupiter appear as big as the moon does from Earth? Would it appear to be a disk to the naked eye, or would it be star-like?

Here are some back-of-the-envelope calculations.

The maximum apparent magnitude of Jupiter is -2.94, which is observed when it's closest to Earth (4.2 AU). Mars can get as close to Jupiter as 3.68 AU. Since the flux is inversely proportional to distance squared, Jupiter will be 30% brighter on Mars than it is on Earth, giving it an apparent magnitude of -3.23. It will still be a bright star-like dot outshined by both Martian moons, Phobos and Deimos with magnitudes of -9 and -5 respectively. It will certainly not be as bright as Earth's Moon seen from Earth, which can be as bright as −12.9.

Here is a detailed article which describes how various celestial bodies look from Mars. They have a picture of Earth, Moon and Jupiter taken by Mars Orbiter Camera (MOC) in 2003, when both Earth and Jupiter were close to Mars:

To put that in perspective: Jupiter would be less bright than Venus is from Earth, and no disk would be visible: It would look like an exceptionally bright star.

The OP asks how big Jupiter "would" appear as seen from Mars. Only one sentence here addresses that.

@RobJeffries: The original question asked how Jupiter would appear from Earth if Jupiter occupied Mars's current orbit. It was (inappropriately) edited to ask instead how Jupiter appears from Mars, then edited back to more or less the original version.

My comment would apply in that case also. Only one sentence vaguely refers to the apparent size. Besides, the answer is clearly talking about how things appear from Mars, so I don't understand your comment @KeithThompson

@RobJeffries: Just summarizing the history, which isn't clear if you just read the current version of the question.

For the sake of clarity I have edited my answer to include the question I was answering. And yeah, I agree that my answer is far from perfect, I'll try to stay more focused on what the question asks next time.