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Size of Sun as seen from Mercury
algorimancer
post Jun 20 2011, 03:02 PM
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I got to wondering about this, considered making my own graphic, then googled and came up with the following, from Burton Mackenzie's blog:

http://1.bp.blogspot.com/_tlXkPX0vMqk/SaTW...ize_diagram.png

So apparently the Sun appears about 3 times as large in Mercury's sky as it does on Earth. I was expecting something much more dramatic.
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ilbasso
post Jun 20 2011, 03:18 PM
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That is interesting indeed. It reminds us how far away even Mercury is from the Sun. So many graphics of the solar system make it look like Mercury is only a couple solar radii away!

I had a similar question a couple of months ago, wondering how far you would have to be from the Moon in order for it to appear the same size as Earth from your vantage point. It was a surprisingly small distance, only about 30,000 miles, if I remember correctly. Both bodies would be about 4 degrees across as seen in your sky.


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Decepticon
post Jun 20 2011, 09:14 PM
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I have a question thats kinda related.

How big does Jupiter look from Io's Surface?
Europa also!
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Phil Stooke
post Jun 20 2011, 09:23 PM
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It's quite simple geometry. For the same object (like the moon), double the distance = half the size, half the distance = double the size and so on, and for different objects at the same distance, twice the size = twice the apparent diameter and so on.

So... for the sun, Mercury's a third of the distance that Earth is from the sun, so three times bigger is what you'd expect.

Jupiter from Io? Jupiter is about 40 times the diameter of the Moon (very roughly) so from the Moon's distance it would look 40 times bigger than the Moon. Then multiply by the appropriate fraction for the ratio of distances - you can go from there yourself, I think.

Phil


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Gsnorgathon
post Jun 20 2011, 09:53 PM
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Bravo, Phil! That's much better than my answer - I was just going to say 2arctan(radius/distance), but your version's a lot easier to work out in one's head.

Apparent diameter in degrees (Moon from Earth = .5):
Jupiter from Io 18.6
Jupiter from Europa 11.8
Jupiter from Ganymede 7.4
Jupiter from Callisto 4.2
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Mr Valiant
post Jun 26 2011, 01:00 AM
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Hey! Jupiter is so big. 4.2 degrees from Callisto, and considering Callisto is pretty much outside
the Jupiter Van Allen belts, it may be the first place humans set foot in the Jupiter system.
Will be an awesome sight.
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Decepticon
post Jun 26 2011, 04:29 AM
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QUOTE
Jupiter from Io 18.6
Jupiter from Europa 11.8


Interesting, Most space art of Jupiter from Io or Europa look incorrect.
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Greg Hullender
post Jun 26 2011, 05:04 PM
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Well, most Earth art makes the moon way, way too big, so I'm not sure what space art is supposed to do. I do get a kick out of how when they show Saturn from any of its moons, artists frequently tilt the planet so the rings can be seen.

Another point on sizes--forgive me if this seems too obvious--but the area is propotional to the square of the diameter. So the sun is not 3x bigger at Mercury--it's 9x bigger.

--Greg
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JohnVV
post Jun 27 2011, 08:47 AM
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a quick look
from Earth
[attachment=24650:sun.earth.jpg]
from Mercury
[attachment=24649:sun.mer.jpg]
earth
[attachment=24651:earth.jpg]
Mercury
[attachment=24652:mer.jpg]
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Bjorn Jonsson
post Jun 28 2011, 09:41 AM
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QUOTE (Decepticon @ Jun 26 2011, 04:29 AM) *
Interesting, Most space art of Jupiter from Io or Europa look incorrect.

This doesn't have to be the case - the field of view varies. There is no single correct size of Jupiter as seen from the Galileans.
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djellison
post Jun 28 2011, 03:29 PM
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Quite. Neither of these views is 'incorrect'
Attached thumbnail(s)
Attached Image
 
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Phil Stooke
post Jun 28 2011, 04:45 PM
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"So the sun is not 3x bigger at Mercury--it's 9x bigger."

Let's not confuse diameter and area! Both are correct.

Phil


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ilbasso
post Jun 28 2011, 08:41 PM
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To be precise, the Sun is the same size. It just LOOKS bigger.


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Fran Ontanaya
post Jun 29 2011, 02:41 AM
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I think it would still have a smaller apparent area from Earth after compensating for the distance, due to Lorenz contraction as the Sun moves across the line of view.


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tedstryk
post Jun 29 2011, 09:58 PM
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QUOTE (ilbasso @ Jun 28 2011, 09:41 PM) *
To be precise, the Sun is the same size. It just LOOKS bigger.


Huh? So are you saying that as I move my hand away from my face my hand doesn't shrink, it just looks smaller? My whole cosmology has just been rocked!


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