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Size Comparism Of The Moons Of The Gas Planets, Moon Systems of the gas giants compared
RNeuhaus
post Nov 18 2005, 09:40 PM
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QUOTE (elakdawalla @ Nov 18 2005, 04:18 PM)
I think it has to do with what the constants are used for by scientists -- physical studies of the bodies, navigation, that kind of thing.  If you're interested in the force of gravity or pressure or something within or just outside a body you're interested in the radial distance from the center.  Same with navigation.  Most geophysical modeling (at least mathematical modeling) is done in polar coordinate systems, which measure spatial positions in radial distance from some center point, typically the center of gravity.  Also many of these things are triaxial ellipsoids, which are described mathematically using their semi-axes, that is, their radii.

You do have to be very careful.  My favorite single source for solar system physical data, the National Space Science Data Center, uses radii for planets/moons and diameters for asteroids -- and I have repeatedly forgotten that fact.  Oops.

--Emily
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Radius for planets and diameters for comet, asteroide or meteor sound logical to me. The smaller bodies do not have a constant radius.

Rodolfo
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jski423
post Nov 18 2005, 10:39 PM
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QUOTE (Toma B @ Nov 18 2005, 08:09 PM)
OK!! That's just great but if you don't mind ;I have one question:

-Why did you write radiuses instead of diameters ?

huh.gif  blink.gif  huh.gif  blink.gif  huh.gif

Maybe this is the "Stupid question of the day"..... unsure.gif
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No, not a stupid question. biggrin.gif I'm just used to working with radius versus diameters.

When I put this together a while ago it wasn't meant for distribution, I made it for myself and my daughter to get her interested in the Solar System. I didn't bother to update anything before posting here.

I am sure this is pretty common knowledge and I don't mean to isult anyone's inteligence but just multiply the radius by 2 to get the diameter. For smaller bodies
I have used the maximum radius and not the mean.

Like I said do what you would like with these and if diameter is what you like you are free to change it. Just do not take credit for it.
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JRehling
post Nov 19 2005, 09:52 AM
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Here is a scale diagram of the satellite orbital distances. The planets are to scale, but each satellite is only one pixel (so dust off your screen). This includes every satellite over some threshold (I forget what that was)... plus Phobos and Deimos. The real upshot here is the revelation that Iapetus is so far out! Also, it's interesting to see that the orbits of Deimos and Charon would fit inside the gas giants.

http://www.cogsci.indiana.edu/farg/rehling...moon-orbits.gif
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Bob Shaw
post Nov 19 2005, 01:13 PM
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Solor Sytsem?

Ooops!

Bob Shaw


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Remember: Time Flies like the wind - but Fruit Flies like bananas!
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David
post Nov 19 2005, 04:12 PM
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QUOTE (JRehling @ Nov 19 2005, 09:52 AM)
Here is a scale diagram of the satellite orbital distances. The planets are to scale, but each satellite is only one pixel (so dust off your screen).
http://www.cogsci.indiana.edu/farg/rehling...moon-orbits.gif
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I think that it needs a few labels! Here's what I can figure out:

MERCURY
VENUS
EARTH: The Moon
MARS: Phobos, Deimos
JUPITER: Amalthea, Io, Europa, Ganymede, Callisto
SATURN: Janus(?), Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Hyperion, and (way over on the right) Iapetus
URANUS: Miranda, Ariel, Umbriel, Titania, Oberon
NEPTUNE: Larissa(?), Proteus, Triton
PLUTO: Charon

The cutoff appears to be around 95km radius.

Now, if I may be so bold as to render the smallest grumble of disapproval about this fine diagram: I realize that it's more artistic to depict Saturn with tilted rings, but in this particular case, when you are showing the satellite systems, and considering that the rings are really part and parcel of Saturn's satellite system and not merely an adornment, it might be more appropriate to straighten them out and get the rings (and Saturn's equator) in line with the satellites' orbital disk.
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tedstryk
post Nov 29 2005, 06:44 PM
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I have been searching and haven't found much in the way of Pallas imagery. Here is an image I constructed through super-res processing of an HST sequenc. The disk is only a few pixels, so it does not show surface details (it missed the planetary camera chip, so it is imaged by the Wide Field portion of WFPC2. The only thing of sigificance is that it does seem to be a pretty round little world, which is consistent with occultation data.



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Patteroast
post Nov 29 2005, 08:17 PM
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Wow, that little orbit comparison reminded me of something I made a while ago.. even more hard to read, though. Pretty much just shows the general idea of the relative distances of the outer planets' moons. I made it some time in 2004. Take a look.

Link

I didn't embed it because it's over 10000 pixels wide. tongue.gif

If it does anything, it really drive home are incredibly far away Neptune's outermost moons are. blink.gif
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Gsnorgathon
post Nov 30 2005, 12:23 AM
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Say - not to drag things off topic here - and it's sort of a size question, in the generic (not technical) sense of magnitude - but...

Has anyone here ever seen a graphical comparison of the albedos of various solar system bodies?

One's always reading about how the Moon's albedo is really quite low, so that images of the Earth and Moon have to amp up the Moon's relative brightness so it can be seen, or about how such-and-such object (comet, asteroid, TNO) is "black as coal". But I've never seen a graphical comparison, or an attempt to relate albedos other than coal or fresh snow to ordinary objects.
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JRehling
post Nov 30 2005, 01:00 AM
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QUOTE (Gsnorgathon @ Nov 29 2005, 04:23 PM)
Say - not to drag things off topic here - and it's sort of a size question, in the generic (not technical) sense of magnitude - but...

Has anyone here ever seen a graphical comparison of the albedos of various solar system bodies?

One's always reading about how the Moon's albedo is really quite low, so that images of the Earth and Moon have to amp up the Moon's relative brightness so it can be seen, or about how such-and-such object (comet, asteroid, TNO) is "black as coal". But I've never seen a graphical comparison, or an attempt to relate albedos other than coal or fresh snow to ordinary objects.
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FWIW, the different bodies receive different levels of solar illumination, so the Moon is actually brighter per unit surface area than, say, Uranus.

One thing that makes it hard to display albedos accurately is that monitors just aren't bright enough -- not even close. A white screen in a dark room is much dimmer than coal in daylight. As it happens, Uranus is about the brightness of a monitor, but the first six planets and their moons are lit significantly more brightly. So you'd have to use bar graphs or something to represent the brightnesses.

I once observed seven planets and the Moon through my telescope on the same night, sometimes getting a peek at two planets as fast as I could point (~2 min). Of course, rare (unless the Moon is one body) conjunctions let you compare two bodies at the same time through a low magnification. You can find pictures of Moon-planet occultations and compare away...
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Gsnorgathon
post Nov 30 2005, 01:38 AM
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QUOTE (JRehling @ Nov 30 2005, 01:00 AM)
FWIW, the different bodies receive different levels of solar illumination, so the Moon is actually brighter per unit surface area than, say, Uranus.
...
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You're right - that's a whole 'nuther kettle o' fish. There's albedo, and then there's brightness.
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