# Thread: Appearance of sun on Mars as compared to its appearance on Earth.

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## Appearance of sun on Mars as compared to its appearance on Earth.

Hello,
I'm new to this forum, just joined, but old to this world.
On Mars, how would the sun appear, in size, as compared to its size appearance on Earth?

Thank you,
Patrick

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Hey, Patrick!

Mars is about 1.5 times as far from the Sun as Earth is,
so the Sun's angular diameter on Mars is 1/1.5, or 2/3
what it is on Earth. 2/3rds the angular diameter means
4/9ths (a bit less than half) the angular area, so the Sun
is 4/9ths as bright on Mars as it is on Earth.

Next question.

-- Jeff, in Minneapolis

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Originally Posted by Jeff Root
Hey, Patrick!

Mars is about 1.5 times as far from the Sun as Earth is,
so the Sun's angular diameter on Mars is 1/1.5, or 2/3
what it is on Earth. 2/3rds the angular diameter means
4/9ths (a bit less than half) the angular area, so the Sun
is 4/9ths as bright on Mars as it is on Earth.

Next question.

-- Jeff, in Minneapolis
Thank you. Isn't 2/3 equal to 4/6 ?

4. Originally Posted by potoole
Thank you. Isn't 2/3 equal to 4/6 ?
Yes, but 2/3 squared is 4/9.

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There is a photo on wikipedia on a sunset on Mars:

http://en.wikipedia.org/wiki/File:MarsSunset.jpg

Unfortunately the scale is very hard to determine, but at least it gives you an idea of the colors that would be expected.

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## A note of thanks.

Thank you for the information.

Patrick

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The area of a figure is proportional to the square of its
linear dimensions. In this case the angular diameter of
the Sun as seen from Mars is 2/3 of what is seen from
Earth, and 2/3 squared = 2 squared / 3 squared = 4/9.

The diameter is 2/3, the area is less than 1/2.

-- Jeff, in Minneapolis

8. Bearing in mind that the Sun covers only 4/9ths as much of Mars' sky as it does on Earth, it is only a little bit bigger than Phobos in the sky - as could be seen when Phobos transits in front of the Sun's disk.

See this interesting page showing transits of both Phobos and Deimos.
http://astrobob.areavoices.com/2011/...-dime-a-dozen/

9. Originally Posted by eburacum45
Bearing in mind that the Sun covers only 4/9ths as much of Mars' sky as it does on Earth, it is only a little bit bigger than Phobos in the sky - as could be seen when Phobos transits in front of the Sun's disk.

See this interesting page showing transits of both Phobos and Deimos.
http://astrobob.areavoices.com/2011/...-dime-a-dozen/
Nice!

But looking at those photos, and using those figures, I'd say that Phobos appears less than half the angular area of the sun, from the surface of Mars. The picture looks even smaller.

10. One oddity is very noticeable in the image of the links above: a blue halo around the Sun. This is quite different than what we see here in our atmosphere. The rest of the Martian sky is not blue but a brownish color, contrary to what was originally expexcted.

The reason for this somewhat odd color reversal seems to be found in the particle sizes in the atmosphere of Mars. There seems to be enough particles of a size that allows for red light to scatter away, and sized too large to cause blue light to scatter -- blue scattering (Rayleigh) is what takes place in our atmosphere. This kind of scattering is called selective scattering, though it may have a fancier name.

Another quirk is that the surface brightness -- this is the amount of brightness per unit area -- of the Sun as seen from Mars is a little brighter than what we Earthlings see, oddly enough. Overall brightness is about half as much as Earth's view, but the apparent size is also about half, so the unit area brightness is still horribly bright. Also, there is much less atmosphere on Mars so sunlight is not diminished quite as much, though the difference between horribly bright and severely bright don't matter much, I suppose.

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I'm wondering, since Mars is smaller than Earth, its horizon, to an Earthling, would appear to be closer than Earth's horizon. Due to the smaller appearance of the sun on Mars, would that (the closer appearance of the Mars Horison) add to the 'illusion' of the sun being even smaller looking on Mars? Or, would it be the other way around?

12. Originally Posted by potoole
I'm wondering, since Mars is smaller than Earth, its horizon, to an Earthling, would appear to be closer than Earth's horizon. Due to the smaller appearance of the sun on Mars, would that (the closer appearance of the Mars Horison) add to the 'illusion' of the sun being even smaller looking on Mars? Or, would it be the other way around?
I would not expect any significant visual difference. True, there is somewhat more horizon dip and departure from a great circle, but it still is very slight from eye level above the ground. I don't think it would be noticed if one was not looking for it. In my case, my glasses have so much pincushion distortion that all bets are off concerning the appearance of the horizon.

13. Illusions of that sort, which are not caused by physical processes like reflection or refraction, are sometimes specific to the individual.

14. Would shadows look a bit different due to the smaller apparent size of the sun? I think that shadows on Mars might appear to spread out a bit more than on earth.

15. Originally Posted by Clive Tester
Would shadows look a bit different due to the smaller apparent size of the sun? I think that shadows on Mars might appear to spread out a bit more than on earth.
I would expect just the opposite - sharper edges.

16. Originally Posted by Hornblower
I would expect just the opposite - sharper edges.
That would be aesthetically very different from a desert of earth. I guess a thinner atmosphere would mean less scattered light from the sky. Thus sharper(from a smaller sun) and deeper shadows (from less back lighting): it might look like the stark and eerie lunar shadows.

17. Originally Posted by Clive Tester
That would be aesthetically very different from a desert of earth. I guess a thinner atmosphere would mean less scattered light from the sky. Thus sharper(from a smaller sun) and deeper shadows (from less back lighting): it might look like the stark and eerie lunar shadows.
That thin atmosphere is very dusty and appears to make about as bright a sky as we have on the ground here, at least in the lander images I have seen. My guess is something similar to what I saw on a sunny day in Los Angeles 50 years ago, when the smog was really heavy.

18. Thanks for clearing-up the....fog (in my mind). I can't say how many times I've watched visitors look surprised when they see that the Alamo is not out in the cactus countryside, but in downtown San Antonio. Movies do make lasting impressions.

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