How bright would the moon be from Mars?

[kirkster501]

....or Jupiter?

Would it be a naked eye object? If you had, say a 8" reflector on Mars and pointed it at the moon, would you see surface detail?

Steve

[Steve Ward]

Just had a look on Stellarium ,

Here's a shot of Earth and Moon from Mars with SPC900NC through Mak180Pro and 2 x Barlow.

[JamesF]

Marginally less bright than Mars is from Earth, I imagine. The average albedo of Mars is around 0.15 whereas the average albedo of the Moon is about 0.12. Which surprises me. I thought the Moon would be brighter than Mars.

James

[JamesF]

Oh, and of course they're about the same size.

James

[kirkster501]

Thanks! Never knew you could do that in stellarium! Learn something all the time at SGL

[Steve Ward]

Click on the location box at the top of the left hand margin ( or F6 )

At the bottom right of the box there's a 'Planet' option , you can enter anywhere you'd like to view from ,

I've just added a list of comets to keep track of C/2011 L4 and they've all been added to the list so I had a quick Solar fly-by like you do.

You can even place yourself on Jupiter's moons and give yourself a great view of the GRS . . .

[JulianO]

This page http://en.wikipedia.org/wiki/Astronomy_on_Mars gives some good info. Specifically

An observer on Mars would be able to see the Moon orbiting around the Earth, and this would easily be visible to the naked eye. By contrast, observers on Earth cannot see any other planet's satellites with the naked eye

[acey]

The Moon seen from Mars with the naked eye would obviously be point-like, since Mars seen from Earth is point-like, and Mars is bigger than the Moon. So the Moon would look like a star, and the question is how bright this "star" would be.

Let m1 be the apparent magnitude of the Moon as seen from Earth (distance d1), and m2 be the apparent magnitude as seen from Mars (distance d2). Then

m2 = m1 + 5log(d2/d1)

Mean Earth-Moon distance d1 is approximately 3.8 x 10^5 km, and mean apparent magnitude of full Moon seen from Earth is m1 = -12.7 approximately.

Earth-Mars distance is about 5.5 x 10^6 km at closest approach. Taking this as d2, then the brightest possible Moon magnitude seen from Mars would be

m2 = -12.7 + 5log(55/3.8) = -6.9

which is brighter than the International Space Station seen from Earth (about mag -6). But that's for a fully illuminated lunar disc, whereas an observer on Mars is always going to see a crescent Moon (since a full one would be on the opposite side of the Sun), and that will be fainter.

A half Moon is about magnitude -10 from Earth, and the mean Earth-Mars distance is about 2.3 x 10^6 km. Then this gives an "average" magnitude for the Moon seen from Mars as

m2 = -10 + 5log(230/3.8) = -1.1.

which is a bit fainter than Sirius (which is about mag -1.5). So in general the Moon will be a conspicuous naked-eye object as seen from Mars.

[ronin]

Since Mars is outside the earths orbit surely mainly the dark side of the moon would be presented to a Martian observer at out closest position, or you would have to wait for Earth and Mars to be on opposite sides of the sun and then it is a huge distance and the sun would be up in the Martian sky (their daylight).

As Mars/Earth come together and pass then just cresents would be apparent.

[Tiki]

So in general the Moon will be a conspicuous naked-eye object as seen from Mars.

This seems too bright as Mars is never anything like that conspicuous from earth.

I just did a very quick calculation and got about mag 4 for a half-moon as seen from Mars.

[Steve Ward]

According to Stellarium the Moon is Mag 2.55 from Mars.

[acey]

It's all going to depend on the Moon phase as seen from Mars, and the Moon-Mars distance, both of which vary a lot. My estimate of about -1 was based on an assumption of a half-illuminated moon seen when the Moon-Mars distance is at its mean value. The actual figure at any given time could be higher or lower. Tiki, show your calculation - maybe I made a slip.

According to Wikipedia, Mars has maximum brightness -2.9 as seen from Earth, which is about 5 times brighter than my estimate of a "typical" Moon brightness seen from Mars.

Wikipedia gives minimum Mars brightness 1.84 as seen from Earth. This is about 15 times fainter than my figure for a "typical" Moon brightness, but about twice as bright as the figure that Stellarium apparently gives (though we don't know what conditions are being assumed for the Stellarium figure).

Tiki, even if the Moon were mag 4 seen from Mars, it would still be a conspicuous naked-eye object. Unless they put a lot of streetlights on Mars.

[Tiki]

I just did a very quick calculation and got about mag 4 for a half-moon as seen from Mars.

The Mars-Moon distance at Martian half-moon is approx. 275*10^6km. The half-moon at mag -10 is viewed from Earth at approx. 0.384*10^6 km. The half-moonlight on Mars is therefore about 500,000 times less intense than it is on Earth. This reduction in intensity corresponds to approx. 14 clicks on the stellar magnitude scale.

@ Acey. I think you may have an erroneous decimal point in your quoted Earth-Mars distance.

[acey]

The Mars-Moon distance at Martian half-moon is approx. 275*10^6km. The half-moon at mag -10 is viewed from Earth at approx. 0.384*10^6 km. The half-moonlight on Mars is therefore about 500,000 times less intense than it is on Earth. This reduction in intensity corresponds to approx. 14 clicks on the stellar magnitude scale.

@ Acey. I think you may have an erroneous decimal point in your quoted Earth-Mars distance.

Yes, you're right, thanks. With your figures the magnitude would be

-10 + 5log(275/0.384) = 4.3.