APOD: Six Moons of Saturn (2012 Apr 14)

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APOD: Six Moons of Saturn (2012 Apr 14)

Post by APOD Robot » Sat Apr 14, 2012 4:05 am

Image Six Moons of Saturn

Explanation: How many moons does Saturn have? So far 62 have been discovered, the smallest only a fraction of a kilometer across. Six of its largest satellites can be seen here, though, in a sharp Saturnian family portrait taken on March 9. Larger than Earth's Moon and even slightly larger than Mercury, Titan has a diameter of 5,150 kilometers and starts the line-up at the lower left. Continuing to the right across the frame are Mimas, Tethys, [Saturn], Enceladus, Dione, and Rhea at far right. Saturn's first known natural satellite, Titan was discovered in 1655 by Dutch astronomer Christiaan Huygens, while most recently the satellite provisionally designated S/2009 S1 was found by the Cassini Imaging Science Team in 2009. Tonight, Saturn reaches opposition in planet Earth's sky, offering the best telescopic views of the ringed planet and moons.

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Re: APOD: Six Moons of Saturn (2012 Apr 14)

Post by Beyond » Sat Apr 14, 2012 4:23 am

Man... Datsa lotta moons :!:
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Re: APOD: Six Moons of Saturn (2012 Apr 14)

Post by Ann » Sat Apr 14, 2012 5:07 am

Very nice picture! I love the fact that tiny Enceladus, which would fit across Great Britain, shows up so clearly. That's what a high surface brightness does for you! Enceladus, kinglet of albedo! :D

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Re: APOD: Six Moons of Saturn (2012 Apr 14)

Post by Flase » Sat Apr 14, 2012 7:43 am

I'd like to sit in a hotel orbiting Saturn and look at the view

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Re: APOD: Six Moons of Saturn (2012 Apr 14)

Post by orin stepanek » Sat Apr 14, 2012 1:01 pm

the smallest only a fraction of a kilometer across.
How large does a moon have to be to get counted? If you counted every rock and snow ball in Saturn's ring the number would be uncountable! :roll: I'm guessing that there are a lot of then between the size of the smallest one listed and tapering down in size to the dust that form the rings. :wink:
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Re: APOD: Six Moons of Saturn (2012 Apr 14)

Post by Moonlady » Sat Apr 14, 2012 3:07 pm

Being Moonlady makes me the expert about moons.
I am 1.50 m so every object big as me and bigger as me turning around a planet counts as a moon :lol:

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Re: APOD: Six Moons of Saturn (2012 Apr 14)

Post by Chris Peterson » Sat Apr 14, 2012 4:10 pm

orin stepanek wrote:
the smallest only a fraction of a kilometer across.
How large does a moon have to be to get counted? If you counted every rock and snow ball in Saturn's ring the number would be uncountable! :roll: I'm guessing that there are a lot of then between the size of the smallest one listed and tapering down in size to the dust that form the rings. :wink:
If it's a body in orbit around a planet, it's a moon. Material in rings is sort of an exception to that. Otherwise, it could be thousands of kilometers across or it could be dust. Keep in mind that below a certain size, objects are likely to be in fairly unstable orbits, meaning that their tenure as "moons" will be quite short (like the occasional extra moons that Earth periodically acquires).
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Post by neufer » Sat Apr 14, 2012 4:15 pm

Chris Peterson wrote:
orin stepanek wrote:
the smallest only a fraction of a kilometer across.

How large does a moon have to be to get counted? If you counted every rock and snow ball in Saturn's ring the number would be uncountable! :roll: I'm guessing that there are a lot of then between the size of the smallest one listed and tapering down in size to the dust that form the rings. :wink:
If it's a body in orbit around a planet, it's a moon. Material in rings is sort of an exception to that. Otherwise, it could be thousands of kilometers across or it could be dust. Keep in mind that below a certain size, objects are likely to be in fairly unstable orbits, meaning that their tenure as "moons" will be quite short (like the occasional extra moons that Earth periodically acquires).
http://en.wikipedia.org/wiki/Natural_satellite wrote:
<<A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. There is not an established lower limit on what is considered a moon. Every body with an identified orbit, some as small as a kilometer across, has been identified as a moon, though objects a tenth that size within Saturn's rings, which have not been directly observed, have been called moonlets. Small asteroid moons, such as Dactyl, have also been called moonlets. The upper limit is also vague. Two orbiting bodies are sometimes described as a double body rather than primary and satellite. Asteroids such as 90 Antiope are considered double asteroids, but they have not forced a clear definition of what constitutes a moon. Some authors consider the Pluto-Charon system to be a double (dwarf) planet. The most common dividing line on what is considered a moon rests upon whether the barycentre is below the surface of the larger body, though this is somewhat arbitrary, as it relies on distance as well as relative mass.

Formally classified moons include 173 planetary satellites orbiting six of the eight planets, and seven orbiting three of the five IAU-listed dwarf planets. As of January 2012, over 200 minor planet moons have been discovered. There are 76 in the asteroid belt (5 with two satellites), 4 Jupiter trojans, 37 near-Earth objects and 9 Mars-crossers. There are also 76 known moons of trans-Neptunian objects. Some 150 additional small bodies were observed within rings of Saturn, but they were not tracked long enough to establish orbits.>>
http://en.wikipedia.org/wiki/Moons_of_Saturn#Ring_moonlets wrote: <<In 2006, four tiny moonlets were found in Cassini images of the A Ring. Before this discovery only two larger moons had been known within gaps in the A Ring: Pan and Daphnis. These are large enough to clear continuous gaps in the ring. In contrast, a moonlet is only massive enough to clear two small—about 10 km across—partial gaps in the immediate vicinity of the moonlet itself creating a structure shaped like an airplane propeller. The moonlets themselves are tiny, ranging from about 40 to 500 meters in diameter, and are too small to be seen directly. In 2007, the discovery of 150 more moonlets revealed that they (with the exception of two that have been seen outside the Encke gap) are confined to three narrow bands in the A Ring between 126,750 and 132,000 km from Saturn's center. Each band is about a thousand kilometers wide, which is less than 1% the width of Saturn's rings. This region is relatively free from the disturbances related to resonances with larger satellites, although other areas of the A Ring without disturbances are apparently free of moonlets. The moonlets were probably formed from the breakup of a larger satellite. It is estimated that the A Ring contains 7,000–8,000 propellers larger than 0.8 km in size and millions larger than 0.25 km.

During late July 2009, a moonlet was discovered in the B Ring, 480 km from the outer edge of the ring, by the shadow it cast. It is estimated to be 300 m in diameter. Unlike the A Ring moonlets, it does not induce a 'propeller' feature, probably due to the density of the B Ring.

Similar moonlets may reside in the F Ring. There, "jets" of material may be due to collisions, initiated by perturbations from the nearby small moon Prometheus, of these moonlets with the core of the F Ring. One of the largest F-Ring moonlets may be the as-yet unconfirmed object S/2004 S 6. The F Ring also contains transient "fans" which are thought to result from even smaller moonlets, about 1 km in diameter, orbiting near the F Ring core.>>
.
http://en.wikipedia.org/wiki/Aegaeon_%28moon%29 wrote: <<Aegaeon (Greek Αιγαίων), also Saturn LIII (provisional designation S/2008 S 1), is a natural satellite of Saturn. Its discovery was announced by Carolyn Porco of the Cassini Imaging Science Team on March 3, 2009, from observations taken on August 15, 2008.

Aegaeon orbits within the bright segment of Saturn's G Ring, and is probably a major source of the ring. Debris knocked off the moon forms a bright arc near the inner edge, which in turn spreads to form the rest of the ring. Aegaeon orbits in a 7:6 resonance with Mimas, which causes a ≈ 4-year oscillation of ≈ 4 km in its semi-major axis. Assuming it has the same albedo as Pallene, it is estimated to be half a kilometer in diameter. It orbits Saturn at an average distance of 167,500 km in 0.80812 days, at an inclination of 0.001° to Saturn's equator, with an eccentricity of 0.0002.

It is named after Ægæon, one of the hecatonchires. The Hecatonchires, or Hekatonkheires (Ἑκατόγχειρες) "Hundred-Handed Ones," Latinised Centimani), were figures in an archaic stage of Greek mythology, three giants of incredible strength and ferocity that surpassed that of all Titans whom they helped overthrow. Their name derives from the Greek ἑκατόν (hekaton; "hundred") and χείρ (kheir; "hand"), "each of them having a hundred hands and fifty heads." Hesiod's Theogony reports that the three Hekatonkheires became the guards of the gates of Tartarus.

According to Hesiod, the Hekatonkheires were children of Gaia (Earth) and Uranus (sky). Their names were Briareus (Βριάρεως) the Vigorous, also called Aigaion (Αἰγαίων), Latinised as Aegaeon, the "sea goat", Cottus (Κόττος) the Striker or the Furious, and Gyges (Γύγης) or Gyes (Γύης) the Big-Limbed. If some natural phenomena are symbolised by the Hekatoncheires then they may represent the gigantic forces of nature that appear in earthquakes and other convulsions or in the motion of sea waves.

Soon after they were born their father Uranus threw them into the depths of Tartarus because he saw them as hideous monsters. In some versions Uranus saw how ugly the Hekatonkheires were at their birth and pushed them back into Gaia's womb, upsetting Gaia greatly, causing her great pain and setting into motion the overthrow of Uranus by Cronus (a.k.a, Saturn), who later imprisoned them in Tartarus. The Hekatonkheires remained there, guarded by the dragon Campe, until Zeus rescued them, advised by Gaia that they would serve as good allies against Cronus and the Titans. During the War of the Titans the Hekatonkheires threw rocks as big as mountains, one hundred at a time, at the Titans, overwhelming them.

Other accounts make Briareus or Aegaeon one of the assailants of Olympus, who, after his defeat, was buried under Mount Aetna. Briareus is mentioned in the Divine Comedy poem Inferno as one of the Giants in the Ninth Circle of Hell (Inferno XXXI.99). The giant is also mentioned in Cervantes' Don Quixote, in the famous episode of the windmills.>>
Art Neuendorffer

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Re: APOD: Six Moons of Saturn (2012 Apr 14)

Post by marsmallow » Sat Apr 14, 2012 6:49 pm

If I go to photografer Rafels website he also have Jupiter picture with 3 versions of the planet taken the same night. One of tem seems to be upside down though, the first one. Should I belive this Saturn photo when he mix things upside down to make pictures look interesting?

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Re: APOD: Six Moons of Saturn (2012 Apr 14)

Post by bystander » Sat Apr 14, 2012 8:44 pm

marsmallow wrote:If I go to photografer Rafels website he also have Jupiter picture with 3 versions of the planet taken the same night. One of tem seems to be upside down though, the first one. Should I belive this Saturn photo when he mix things upside down to make pictures look interesting?
I'm not sure what it is you are asking. The image of Jupiter that is "upside down", as you say, is the way Jupiter would appear through most telescopes. The other two images have been rotated so that Jupiter's North Pole is up.
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Re: APOD: Six Moons of Saturn (2012 Apr 14)

Post by Marsmallow » Sat Apr 14, 2012 8:52 pm

bystander wrote:
marsmallow wrote:If I go to photografer Rafels website he also have Jupiter picture with 3 versions of the planet taken the same night. One of tem seems to be upside down though, the first one. Should I belive this Saturn photo when he mix things upside down to make pictures look interesting?
I'm not sure what it is you are asking. The image of Jupiter that is "upside down", as you say, is the way Jupiter would appear through most telescopes. The other two images have been rotated so that Jupiter's North Pole is up.
Most scopes makes the pic receverse left-right, not upside down.

It looks like a gimic to make the combined photos more interesting, giving it a more lively look. But not correct. Jupiter does not spin upside downthe same night.

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Re: APOD: Six Moons of Saturn (2012 Apr 14)

Post by bystander » Sat Apr 14, 2012 8:58 pm

This is what Jupiter normally looks like from ground based telescopes before corrections.
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Re: APOD: Six Moons of Saturn (2012 Apr 14)

Post by Chris Peterson » Sat Apr 14, 2012 9:36 pm

Marsmallow wrote:Most scopes makes the pic receverse left-right, not upside down.

It looks like a gimic to make the combined photos more interesting, giving it a more lively look. But not correct. Jupiter does not spin upside downthe same night.
A telescope may mirror an object with respect to how it appears to the eye. However, the orientation in a telescope is arbitrary, and depends on both where you are on the Earth and what time it is.

I'm not sure how Jupiter got into the discussion.
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Re: APOD: Six Moons of Saturn (2012 Apr 14)

Post by luigi » Sat Apr 14, 2012 9:48 pm

Maybe he is on the South Hemisphere. (He has a photo of the Large Magellan Cloud).
Everything is upside-down here in wonderland :-)

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Re: APOD: Six Moons of Saturn (2012 Apr 14)

Post by alfas » Sat Apr 14, 2012 9:53 pm

Hi friends, my name is Rafael and I am the author of this astronomy picture of the day of six moons of Saturn.

Regarding the picture of Jupiter, and not only Jupiter but all other objetcs in the sky: I live in the Brazil, located in the Shouthern Hemisphere. For us, the entire sky "look" upsidedown compared to the northern sky. Once I posted one image of Orion constallation at the "correct orientation" as viewed here and I read a lot of comments like "wow, orion is upside-down!!" "orion's sword is going to fall"... and others like this. So, sometimes I rotate some images to match north orientation, sometimes not.

Furthermore, putting the telescope in an equatorial mount or altazimuth mount already changes orientation. Just the fact to rotate the camera in the eyepiece holder already changes orientation of anything you are looking at.

Concerning the rotation in the same night, any object in the sky DOES rotate that much if you track it all night with an altazimuth mount just because the entire sky rotates (including any planet one it, thankfully). But it does not rotate if you track this object with an equatorial one. Anyway, that's not what I meant to show in this image. Depending the position you are located on Earth and depending how high Jupiter is at the sky, it will have a different orientarion.

The truth is that there's no such a thing like up or down at the space. Jupiter does not have a correct orientation as it appears in real life for the earth residents as it changes every second. It has, although, a north and a south pole designed by us. That does not mean that the north pole will be oriented towards the upper part of the field of view.

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Re: APOD: Six Moons of Saturn (2012 Apr 14)

Post by Marsmallow » Sat Apr 14, 2012 9:56 pm

bystander wrote:This is what Jupiter normally looks like from ground based telescopes before corrections.
Please try looking trough a Star diagonal, that is most frequent on telescopes for astronomy, or Google star diagonal.

That's a mirror with 45 degere angle, prefered over a prism diagonal with correct image, as the prism does reduce both sharpness and contrast. For daytime and terrestial use a prism is more common though. But when hunting the rare photons in the night sky the star diagonal is preferred. Upside-down is correct but righ left is reversed.

The view on planets might shift if you cross equator line. I live in the north hemisphere. But a star diagonal still gives a left-right switch independent of what part of the globe you use it.

But if you use a telescope of very old style, like Gallelio, the result would actally be upside down like you said when looking into the diagonal and correct with out it! But most modena scopes produces a picure that is upside down and revese left right without a diagonal, and only one is fixed by the single mirror.

-But this is a side track on technical stuff, my first point was that if things appear to be mixed and placed differently in the combined picture on Jupiter on purpose or not, can I then trust this picture of Saturn and the moons? (ie. I do not see the photographer jumping from south to north in the same night to have both views.)

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Re: APOD: Six Moons of Saturn (2012 Apr 14)

Post by bystander » Sat Apr 14, 2012 10:07 pm

<sarcasm>No, obviously, this photographer is trying to mislead the public.</sarcasm>
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Re: APOD: Six Moons of Saturn (2012 Apr 14)

Post by alfas » Sat Apr 14, 2012 10:18 pm

Marsmallow wrote:-But this is a side track on technical stuff, my first point was that if things appear to be mixed and placed differently in the combined picture on Jupiter on purpose or not, can I then trust this picture of Saturn and the moons? (ie. I do not see the photographer jumping from south to north in the same night to have both views.)
Use Stellarium or any other software that simulates the entire sky stuff at the time and date that the picture was taken and you will have your answer.

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Re: APOD: Six Moons of Saturn (2012 Apr 14)

Post by Anthony Barreiro » Mon Apr 16, 2012 7:25 pm

This is a lovely picture of Saturn and his moons. Saturday night I was able to observe Saturn with an eight-inch schmidt cassegrain telescope. There was slight haze and the seeing was below average. But the rings were very bright, banding was apparent on the planet's surface, and Titan, Rhea, and Iapetus were visible. It was a good night.
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Re: APOD: Six Moons of Saturn (2012 Apr 14)

Post by Anthony Barreiro » Mon Apr 16, 2012 7:30 pm

By the way, in this picture Saturn's north pole is toward the bottom / right of the picture. You can tell by the orientation of the rings against the planet and the remnant of the recent northern storm on the surface of the planet.
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Re: APOD: Six Moons of Saturn (2012 Apr 14)

Post by orin stepanek » Mon Apr 16, 2012 9:18 pm

Chris and Art! Thanks for the info on moon sizes! 8-) :D :wink:
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Re: APOD: Six Moons of Saturn (2012 Apr 14)

Post by Marshmallow » Tue Apr 17, 2012 4:37 pm

alfas wrote:
Marsmallow wrote:-But this is a side track on technical stuff, my first point was that if things appear to be mixed and placed differently in the combined picture on Jupiter on purpose or not, can I then trust this picture of Saturn and the moons? (ie. I do not see the photographer jumping from south to north in the same night to have both views.)
Use Stellarium or any other software that simulates the entire sky stuff at the time and date that the picture was taken and you will have your answer.
I'm sorry if I mix things, I was commenting on a Jupiter photo on his home page, wich could be found by clicking the photographers name. The pictures contains 3 different images of Jupiter, taken the very same night. What I did not understand that north/south was reversed on one of them, but not on the other two.

This could maybe happen when a german equatorial mount switches side when passing the north-south line on earth, and hence the telescope is rotaded 180 degrees. If this is not corrected/compensated for when making the beatiful 3 planet picture the result would be that north/south on Jupiter is switched depending on if the pic is taken after/before the rotation. You can see the red spot position is changed for one in the picture.

(Regarding the direction of the Saturnus rings they look this way if you are on the south side of the earth, it is easy to check with Sky safari or Stellarium, by setting the right coordinates for his home town. From north side of earth the are reversed.)

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Re: APOD: Six Moons of Saturn (2012 Apr 14)

Post by alfas » Thu May 31, 2012 1:30 am

No need to sorry, I'm glad it's clear now. =)

Regards

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