Earth from Saturn - other stars? Moon? (APOD 27 Sep 2006)

Jim · Post by **Jim** » Wed Sep 27, 2006 11:31 am

Which dot is earth?

There are two in the picture ... one is faint ... both are on the left

Wadsworth · Post by **Wadsworth** » Wed Sep 27, 2006 1:02 pm

I imagine that it would be the brighter of the two dots.

1) Because it's relative brightness is comparative to that of Saturn's from an earth orbit.

2) It's location with reference to where the sun must be if Cassini is in Saturn's shadow.

3) I think the author would have noted otherwise if Earth wasn't the second brightest object in the photo.

vob · Post by **vob** » Wed Sep 27, 2006 1:48 pm

The caption says that the bulge in the inset image is Earth's moon, but are you sure? It doesn't look like much and it seems way too close. Isn't the Earth about 8,000 miles wide, and a quarter million miles from the moon? I suppose if the moon were almost directly behind (or in front of) the Earth, it would be possible. Can we find out for certain one way or another? Does the photo have a time stamp?

orin stepanek · Post by **orin stepanek** » Wed Sep 27, 2006 1:51 pm

Jim wrote:Which dot is earth?

There are two in the picture ... one is faint ... both are on the left

http://antwrp.gsfc.nasa.gov/apod/ap060927.html

I only see one on the right.

I'm glad we got all the prochlorococcus using up the CO2. 8)

Orin

BBK · Post by **BBK** » Wed Sep 27, 2006 1:53 pm

If only one blue dot is earth, what is the other one, directly left of Saturn?

BMAONE23 · Post by **BMAONE23** » Wed Sep 27, 2006 1:58 pm

That is Saturns Moon Enceladus in the rings http://www.nasa.gov/mission_pages/cassi ... 08324.html

Jim · Post by **Jim** » Wed Sep 27, 2006 2:55 pm

Thanks ...

iamlucky13 · Post by **iamlucky13** » Wed Sep 27, 2006 3:55 pm

I'm pretty sure, as you suggested, it's just nearly inline with the earth. The odds are pretty much even for the moon being in any given spot in its orbit at the time a random picture is taken.

You can confirm it, but it will take some legwork. You should be able to find a copy of the image on http://saturn.jpl.nasa.gov with a timestamp. Then if you dig around you can find a solar system map with a current display of the location of saturn, and you can find out from a variety of sources (even tide tables) where the moon was in relation to the earth and sun.

Ken Blackwell · Post by **Ken Blackwell** » Wed Sep 27, 2006 4:23 pm

How can Saturn block the sun from the earth since Saturn is behind (in relation to the sun) earth.

Martin · Post by **Martin** » Wed Sep 27, 2006 4:41 pm

OMG!!!! It is an alien mother ship blasting some more multiple ringed craters!

BMAONE23 · Post by **BMAONE23** » Wed Sep 27, 2006 4:44 pm

Saturn is actually blocking the sun from Cassini's viewpoint. Cassini is in Saturns shadow which allows it to view the Earth.

danaswart · Post by **danaswart** » Wed Sep 27, 2006 4:57 pm

How come you can only see earth? Where are the rest of the stars?

Qev · Post by **Qev** » Wed Sep 27, 2006 4:57 pm

Well, also bear in mind that at the distance of Saturn, the separation between the Earth and Moon (at its widest) is only about 1/30th the angular diameter of the full Moon on our night sky...

orin stepanek · Post by **orin stepanek** » Wed Sep 27, 2006 5:43 pm

My gosh! we have 4 separate threads on the same topic.

Orin

Wadsworth · Post by **Wadsworth** » Wed Sep 27, 2006 5:49 pm

Read this and let us know what you think.

Wadsworth · Post by **Wadsworth** » Wed Sep 27, 2006 5:54 pm

Martin wrote:OMG!!!! It is an alien mother ship blasting some more multiple ringed craters!

Not to reinforce possibly derogatory comments but.. HAHAHAHAA that made me crack up.

BMAONE23 · Post by **BMAONE23** » Wed Sep 27, 2006 7:33 pm

This is a link to the Apollo moon image. The only modification that I made to the image was to enlarge it to 10 X 10. The faint grey smudges in the black field of space are stars that are still visible but bled out mostly due to the relative brightness of the moon.

http://www.imagehosting.us/index.php?ac ... nt=1636156

http://neo.jpl.nasa.gov/cgi-bin/db?name=2004+MN4 this link shows the locations of saturn and the earth relative to the sun at the time the image was taken. use the zoom out bar at the bottom to help locate saturn then change the date to sept 19. Use the right bar to rotate the image to clarify positions.

orin stepanek · Post by **orin stepanek** » Wed Sep 27, 2006 9:47 pm

BMAONE23 wrote:This is a link to the Apollo moon image. The only modification that I made to the image was to enlarge it to 10 X 10. The faint grey smudges in the black field of space are stars that are still visible but bled out mostly due to the relative brightness of the moon.

http://www.imagehosting.us/index.php?ac ... nt=1636156

http://neo.jpl.nasa.gov/cgi-bin/db?name=2004+MN4 this link shows the locations of saturn and the earth relative to the sun at the time the image was taken. use the zoom out bar at the bottom to help locate saturn then change the date to sept 19. Use the right bar to rotate the image to clarify positions.

BMAONE23; I was very impressed with this photo of the moon! I spent more time checking the moon than looking for background stars.

Orin

dpiddy · Post by **dpiddy** » Wed Sep 27, 2006 11:34 pm

Come on, peeps! You're assuming that the edge of the blurry fuzz ball is the edge of the Earth's surface, which it is not. Just like when you look at a star through a telescope, you're not seeing the surface of the star. You are seeing a bright halo of its light that extends far beyond its actual surface. If it's not the moon, what else might it be?!

dpiddy · Post by **dpiddy** » Wed Sep 27, 2006 11:36 pm

Caption clearly says: "...Cassini imaged a faint dot on the right of the above photograph..." Therefore, Earth is the dot on the right side of the image. The other dot is on the left side of the image.

dpiddy · Post by **dpiddy** » Wed Sep 27, 2006 11:56 pm

"How come you can only see earth? Where are the rest of the stars?"

A. "rest of the stars?" Earth is not a star so "where are the stars?" would be more appropriate.

B. There's at least one other point source of light in that image. Not sure what it is. Might be a moon of Saturn.

C. Stand near a bright light in the middle of the night and look up at the sky. Note how many stars you see. It won't be many. Now move away from the light so that you're in darkness for a couple minutes and look up at the sky again. You'll see many more stars. This explains the lack of stars in the Saturn/Earth image as well as the lack of stars in images from the moon. When you have a very bright object in the same field as a very dim object, your iris will shrink so the bright object doesn't temporarily blind you. This prevents you from noticing the faint object. A camera does the same thing (but with its shutter and/or f stop). Cassini could've been commanded to take a longer exposure so that stars were visible but the light from Saturn would likely overwhelm the photosensors of the camera causing either a washed-out image and/or "blooming" (white streaks caused by the camera's photosites being forced to bleed electrons into neighboring photosites).

D. Images like these are processed by humans to reach a desired effect. It's possible that stars were visible in the images but that the image was processed such that the specific objects of interest are highlighted (Saturn's rings and the dot of Earth), thereby leaving other captured objects no longer visible. But, with such a bright object nearby (Saturn, along with its main rings), the exposure was likely very short and few, if any, stars were captured in the first place.

Best.

Dr. Skeptic · Post by **Dr. Skeptic** » Thu Sep 28, 2006 12:13 am

The telescopic imagery was not designed for deep space viewing. Here's another view home from a mere fraction of the distance. (Mars)

orin stepanek · Post by **orin stepanek** » Thu Sep 28, 2006 12:47 am

Earth is but a dot in this photo. Reading the information notes that the Earth is home of over 6,000,000,000 people. here is an interesting link on the population growth of Earth.
http://www.futuresedge.org/World_Popula ... tails.html
Almost 3X as much as 66 years ago.

BMAONE23 · Post by **BMAONE23** » Thu Sep 28, 2006 4:01 am

The other point source in Saturn's moon Enceladus, or more specifically sunlight reflecting off of the southern polar geysers ejecting ice crystals into its own specific ring.

http://www.nasa.gov/mission_pages/cassi ... 08324.html

BMAONE23 · Post by **BMAONE23** » Thu Sep 28, 2006 4:15 am

This is the respective planetary orientation at the time the image was taken
|
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|...................................moon
|......................................Earth
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|.............................................SUN................................................................................................................jupiter
|........................................................mercury
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|...............................................venus
|
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|................................................................................................mars
|
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|
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|....................................Saturn
|
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|.................................cassini

http://neo.jpl.nasa.gov/cgi-bin/db?name=2004+MN4

Starship Asterisk*

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