6 Years of Saturn (2009 September 4)

[orin stepanek]

http://apod.nasa.gov/apod/ap090904.html

Wow! Saturn's rings almost disappear when looked at edge on. Except for a line going through the equator; you wouldn't know they were there. It's really amazing how thin the rings appear to be.

Orin

[Storm_norm]

crazy question, and I am not sure just how to ask it so here goes.

is the earth ever in all three planetary ring system planes at the same time?
three meaning uranus, neptune, saturn.
in other words, is there ever a point in time where all three ring planes are level with the earth at the same time?

its such a weird question that I am unable to word it the way I am thinking it.
actually, I am assuming that the earth passes through uranus' and neptune's ring plane? if the earth doesn't then this question is definitely one for the blooper reels and I apologize ahead of time for the confusion.

[anabaptiston]

The topmost (2009) image shows a small dot to the right of Saturn, in the ring plane. The next (2008) image also shows a dot to Saturn's right, but apparently below the ring plane. Are these Saturnian moons, artifacts, or coincidental background objects? If they're moons, does anyone know which ones?

[neufer]

The topmost (2009) image shows a small dot to the right of Saturn, in the ring plane. The next (2008) image also shows a dot to Saturn's right, but apparently below the ring plane. Are these Saturnian moons, artifacts, or coincidental background objects? If they're moons, does anyone know which ones?

<<Saturn has at least 61 moons. Titan, the largest, comprises more than 90 percent of the mass in orbit around Saturn, including the rings. Saturn's second largest moon Rhea may have a tenuous ring system of its own. Many of the other moons are very small: 34 are less than 10 km in diameter, and another 14 less than 50 km.>>

[rstevenson]

... its such a weird question that I am unable to word it the way I am thinking it. ...

Perhaps three questions ...

If the ring plane of each planet is thought of as a plane extending out without limit, is there a single point in time/space where the three planes meet.
-- I suspect the answer would be yes, at many points in space/time. But I lack the math to make it definitive.

And is that meeting point in space time ever coincident with the orbit of Earth?
-- Not sure, but since all three planets are much further out than Earth, I suspect such points occur "out there" a lot more often than they do in our neighbourhood.

And is the Earth at that point in its orbit when the meeting point is coincident with the Earth's orbit?
-- No idea.

Not very helpful, am I?

Rob

[bystander]

crazy question, and I am not sure just how to ask it so here goes.

is the earth ever in all three planetary ring system planes at the same time?
three meaning uranus, neptune, saturn.
in other words, is there ever a point in time where all three ring planes are level with the earth at the same time?

its such a weird question that I am unable to word it the way I am thinking it.
actually, I am assuming that the earth passes through uranus' and neptune's ring plane? if the earth doesn't then this question is definitely one for the blooper reels and I apologize ahead of time for the confusion.

Hey, Jupiter has a ring system, too.

When (and if) all three (four with Jupiter) planets are at equinox at the same time, their respective ring planes would all intersect the Sun (and each other at the Sun). However, since since none of the planets have the same inclination with respect to the ecliptic and would not necessarily be in conjunction or opposition, they would not necessarily intersect the Earth at that time. But since the Earth's orbit is between the Sun and the orbits of the gas giants, if the ring planes all intersect Earth's orbit, I would suspect that their ring planes would all intersect at the Earth at some point in time. I would like to see that math. I think your chances of winning the lottery are better.

[Chris Peterson]

is the earth ever in all three planetary ring system planes at the same time?
three meaning uranus, neptune, saturn.
in other words, is there ever a point in time where all three ring planes are level with the earth at the same time?

Maybe you should include Jupiter, as well, since it also has a ring system.

The simple answer is no, they are never all lined up. That would violate some axioms of simultaneity. So a better question might be, just how close could they get? (After all, we're probably interested in seeing them all appear to be lined up, even if at some small level of precision they are not.) It's hard to analyze something like this, but certainly such a thing would be extremely rare- maybe the Solar System isn't old enough for it to have happened. You've got four planets with random orbital periods, inclinations, and planetary axis tilts- five, if you include the requirement for the Earth to be in the right spot as well.

[emc]

This beautiful APOD makes me long for that imagined computer based 3D sharp holographic model of the universe that allows satisfactory speedy travel from one end to the other along with time dilation/compression animation of events in order to satisfy my outer space bound aesthetic and curious ambitions. Don’t want the funky fuzzy holograms I’ve seen but crisp and dense “real” looking planets, moons, stars, nebulae, etc.

Since we can’t even fly (or traverse) to our nearest stellar neighbor without dying first, perhaps someone(s) could build a simulator that allows the next best thing.

[neufer]

is the earth ever in all three planetary ring system planes at the same time?
three meaning uranus, neptune, saturn.
in other words, is there ever a point in time where all three ring planes are level with the earth at the same time?

Maybe you should include Jupiter, as well, since it also has a ring system.

The simple answer is no, they are never all lined up. That would violate some axioms of simultaneity. So a better question might be, just how close could they get? (After all, we're probably interested in seeing them all appear to be lined up, even if at some small level of precision they are not.) It's hard to analyze something like this, but certainly such a thing would be extremely rare- maybe the Solar System isn't old enough for it to have happened. You've got four planets with random orbital periods, inclinations, and planetary axis tilts- five, if you include the requirement for the Earth to be in the right spot as well.

Well, the earth passes through the ring plane of every planet at least twice for each orbit of that planet.

I estimate that about every 100 million years the earth will pass through any given three ring planes during the same earth day but that the Solar System isn't old enough for it the earth to have passed through all four ring planes on the same earth day.

[Isaiah 45:18]

A couple of observations on the images: First, the title of the page is "6 Years of Saturn" with a reference in the caption that they represent 2004-2009, from lower right to upper left. But there are seven images. If the images were taken one year apart, wouldn't the first (lower right) image be 2003? Secondly, the third image up from the right (either '05 or '06 depending on the answer to my first question) is different from the images on either side of it, as it shows no planet shadow cast across the rings behind the planet. If these are all earthbound telescopic photos, it seems the shadow should be there. If not, why not?

[bystander]

A couple of observations on the images: First, the title of the page is "6 Years of Saturn" with a reference in the caption that they represent 2004-2009, from lower right to upper left. But there are seven images. If the images were taken one year apart, wouldn't the first (lower right) image be 2003? Secondly, the third image up from the right (either '05 or '06 depending on the answer to my first question) is different from the images on either side of it, as it shows no planet shadow cast across the rings behind the planet. If these are all earthbound telescopic photos, it seems the shadow should be there. If not, why not?

Where does it say the images were taken 1 year apart? Unfortunately, the apod link from this composite of Saturn views does not provide us with actual image dates. However, this animation link on that page tells us that the upper left picture (Saturn at equinox) is a fabrication.

As for the shadows of Saturn against the rings, I can't say. Maybe they were photshopped out in that picture. The relationship of the shadows would depend on the angles between the Sun, Saturn, and the Earth. If Saturn was in opposition or cunjunction with the Earth, perhaps there wouldn't be a visble shadow (it would be behind Saturn).

Here is a similar sequence from Hubble Heritage for 1996-2000. None of those pictures show much of a shadow from Saturn.

[Storm_norm]

is the earth ever in all three planetary ring system planes at the same time?
three meaning uranus, neptune, saturn.
in other words, is there ever a point in time where all three ring planes are level with the earth at the same time?

Maybe you should include Jupiter, as well, since it also has a ring system.

The simple answer is no, they are never all lined up. That would violate some axioms of simultaneity. So a better question might be, just how close could they get? (After all, we're probably interested in seeing them all appear to be lined up, even if at some small level of precision they are not.) It's hard to analyze something like this, but certainly such a thing would be extremely rare- maybe the Solar System isn't old enough for it to have happened. You've got four planets with random orbital periods, inclinations, and planetary axis tilts- five, if you include the requirement for the Earth to be in the right spot as well.

Well, the earth passes through the ring plane of every planet at least twice for each orbit of that planet.

I estimate that about every 100 million years the earth will pass through any given three ring planes during the same earth day but that the Solar System isn't old enough for it the earth to have passed through all four ring planes on the same earth day.

ok, how about a more general question instead of the specific once in a billion case...
is there a span of time, lets say within an average person's life, ballpark figure 75 years, where the earth passes through each planetary ring plane?
for example, lets say a 10 year old wanted to pick a 75 year span in our solar system's history or future to witness the earth pass through each planetary ring's plane. would such a span in earth's existence exist?

[Chris Peterson]

ok, how about a more general question instead of the specific once in a billion case...
is there a span of time, lets say within an average person's life, ballpark figure 75 years, where the earth passes through each planetary ring plane?
for example, lets say a 10 year old wanted to pick a 75 year span in our solar system's history or future to witness the earth pass through each planetary ring's plane. would such a span in earth's existence exist?

Well, if we simplify things and pretend the Earth isn't orbiting (which in this case is a fair enough approximation), each ringed planet's ring plane passes through the Earth twice on each orbit. So, that's about every 6 years for Jupiter, every 15 years for Saturn, every 42 years for Uranus, and every 82 years for Neptune.

If you imagined these planets as the hands of a clock, then it's easy enough to determine how often they'll all line up (it is a similar problem to predicting conjunctions). The fly in the ointment, however, is that over millions of years almost nothing is deterministic. The planetary inclinations change, and in a not entirely predictable way. The position of each planet's perihelion precesses. All of the planets perturb each other. Trying to figure out how this impacts the probability of an alignment (I know, that was your first question) seems very difficult.

[neufer]

It should be pointed out that Jupiter's axial tilt is a mere 3.13° so the Earth is always fairly close to Jupiter's ring plane.

And the Earth passed through Uranus ring-plane three times on May 2, 2007, Aug. 16, 2007, and Feb. 20, 2008.
Much was learned about Uranus's rings from Keck Telescope observations during this time.

Explanation: Uranus is now slowly approaching its southern autumnal equinox
- the beginning of fall in the southern hemisphere - in 2007.

[Storm_norm]

this is one of those APOD images that reemphasizes the reality of the passage of time. And at the same time demonstrates just how great a name saturn really is. in my mind, it demonstrates the continual march of time that doesn't skip a beat, that saturn is just going about its journey and will eventually tilt enough so that we can see its beauty once again. like a flower that blooms in the spring then lays dormant til the next spring.
Its either a happy moment or a sad moment for astronomers being at a point in time where we are "plane on" with the rings of saturn. The astronomers who want to see the full beauty of the rings will have to wait 7-8 years, but at the same time, the more seasoned astronomers might have been waiting for a "plane on" view since 15 years ago.
this also brings back memories of discussions from school about how often comets come around, especially the orbit of Haley's comet and how its a once in a lifetime even for most people and maybe a twice in a lifetime event for those who live long enough.

[neufer]

this is one of those APOD images that reemphasizes the reality of the passage of time. And at the same time demonstrates just how great a name saturn really is. in my mind, it demonstrates the continual march of time that doesn't skip a beat, that saturn is just going about its journey and will eventually tilt enough so that we can see its beauty once again. like a flower that blooms in the spring then lays dormant til the next spring.

• The flowers that bloom in the spring, Tra la,
  Have nothing to do with the case.
  I've got to take under my ring, Tra la,
  A most unattractive old thing, Tra la,
  With a caricature of a face,
  With a caricature of a face.

[rigelan]

This summer I saw so many things with my binoculars, Neptune, Uranus, Jupiter's Moons, Andromeda Galaxy, that I looked at Saturn for its rings. I had tried and tried and failed, No wonder they weren't visible to my binoculars. Head on! Looks like i'll have to wait a year or so for better images of the rings.

[orin stepanek]

Saturn is so peaceful to look at; yet it and it's moons are so intriguing. 8) What effect would there be to pass through through Saturn's ring planes except visual? I find Saturn very beautiful; only Earth is more so.

Orin

[neufer]

What effect would there be to pass through through Saturn's ring planes except visual?

It's recommended that you aim for one of the gaps (...the bigger the better).
http://cassini-huygens.jpl.nasa.gov/ope ... rrival.cfm

[neufer]

Happy Saturn ring plane crossing day! By Emily Lakdawalla | Sep. 4, 2009

<<During the Saturn ring plane crossing of 1995, astronomers discovered that Prometheus, one of the two tiny moons that shepherd Saturn's F ring, was a full thirty minutes behind where it was predicted to be, twenty degrees off from its expected orbital position. That's the sort of puzzling observation that really gets astronomers thinking. Eventually they figured out that Prometheus is in a chaotic dance with Pandora, the other shepherd of the F ring; the two moons perturb each other's orbits, slowing each other down and speeding each other up.

Ring plane crossings are also excellent times for Earth-based astronomers to study Saturn's fainter rings. In fact, it was during the crossing of 1966 that astronomers discovered the E ring. The E ring has very little in common with the dazzlingly bright A and B rings that are visible in your backyard telescope. The E ring is incredibly faint, but it's also vertically thick, extending thousands of kilometers above and below the ring plane. And it stretches from the edge of the rest of the ring system for hundreds of thousands of kilometers, including the orbits of the moons Mimas, Enceladus, Tethys, Dione, and Rhea. Astronomers found that the E ring was brightest at the orbital position of Enceladus, giving the first clue that tiny Enceladus might be geologically active. We now know that Enceladus has geysers that spew tiny ice crystals into Saturn orbit, and is responsible for creating the vast E ring.

Astronomers have used ring plane crossings to try to determine just how thick the rings are. But it was surprisingly difficult to settle on that number for Saturn. Most estimates came in at about a kilometer thick. Recently, the Cassini orbiter has measured the thickness of Saturn's main A and B rings and found they are much thinner than that, only a few tens of meters thick. Why don't Earth-based astronomers get the same answer? The problem is the F ring, the thin, braided structure that orbits just outside the main A and B rings. It's ordinarily faint and difficult to spot from Earth. But near an equinox, when the Sun strikes the rings from the side, the sparse, dusty particles within the F ring scatter light in all directions, with a goodly fraction of that light bouncing back to observers on Earth. When astronomers tried to measure the thickness of Saturn's rings, they were really measuring the thickness of the F ring.

Some ring plane crossing events are better than others. Sometimes, Earth crosses the ring plane just once, but sometimes there are actually three ring plane crossings in a row, spaced about three months apart. When Earth crosses the ring plane only once, Saturn is usually on the opposite side of the Sun from us and very difficult to observe. But triple crossings happen near opposition, when Saturn is very high in our sky and easy to see.

Ring plane crossings give us a chance to see something that's almost never visible from Earth: the dark side of the rings. Earth is usually on the sunlit side of the rings, since Earth is always within 6 degrees of the Sun as seen from Saturn. This year, when the equinox happened on August eleven, the Sun went to the other side of the rings, so from Earth we were looking upon their unlit face. Today, we pass to the sunlit side again, where we'll be for the next sixteen years. But we can't really enjoy the view very much because this year is one of the duds, a single crossing where Saturn is lost in the Sun's glare.

1995 was a different story. Earth crossed the ring plane in May and spent the next three months on the shadowed side of Saturn's rings. The dense A and B rings were particularly dark, making it much easier to study the smaller moons and the faint C, D, E, and F rings. In August Earth passed back through the plane to the sunlit side. But then Saturn's equinox happened in November, bringing darkness to the rings again for another three months, until Earth passed through the ring plane for the third and final time.

Ring plane crossing events are rare because they depend upon the stately pace of the giant planets' orbits around the Sun, and happen only twice each orbit.

Jupiter's are the most frequent because it has the shortest year, only twelve Earth years long;
the most recent [Jupiter] ring plane crossing was just two months ago.

Saturn ring plane crossings happen every fourteen to seventeen Earth years, but the next good triple crossing isn't until 2038.

Uranus ring plane crossings happen only every forty-two years; the last one was two years ago, when Hubble observations showed that the ring system looked radically different from its appearance to Voyager 2 back in 1986.

Finally, there's distant Neptune, which takes a 165 Earth years to travel around the Sun. The last time we had a chance to observe a Neptune ring plane crossing from Earth, it was 1964, and the charged-coupled device that forms the basis of most modern digital cameras hadn't yet been invented. Our next chance is still another forty years away.>>

[alanfgag]

A couple of observations on the images: First, the title of the page is "6 Years of Saturn" with a reference in the caption that they represent 2004-2009, from lower right to upper left. But there are seven images. If the images were taken one year apart, wouldn't the first (lower right) image be 2003? Secondly, the third image up from the right (either '05 or '06 depending on the answer to my first question) is different from the images on either side of it, as it shows no planet shadow cast across the rings behind the planet. If these are all earthbound telescopic photos, it seems the shadow should be there. If not, why not?

Where does it say the images were taken 1 year apart? Unfortunately, the apod link from this composite of Saturn views does not provide us with actual image dates. However, this animation link on that page tells us that the upper left picture (Saturn at equinox) is a fabrication.

As for the shadows of Saturn against the rings, I can't say. Maybe they were photshopped out in that picture. The relationship of the shadows would depend on the angles between the Sun, Saturn, and the Earth. If Saturn was in opposition or cunjunction with the Earth, perhaps there wouldn't be a visble shadow (it would be behind Saturn).

Here is a similar sequence from Hubble Heritage for 1996-2000. None of those pictures show much of a shadow from Saturn.

The Hubble montage is created from images captured at opposition, when the shadows are minimized and the rings brightened by the Seeliger Effect. One of my images, the third from the bottom, is recorded at opposition also and shows these same phenomena - the others are recorded at different times in each apparition from 2004 - 2009. The exception is the upper left image which is constructed from earlier 2009 pictures and then adapted in Photoshop to give an impression of how saturn might look today if photographed at the same resolution of the other images. Titan was added also (this moon did have a very fine transit along with its shadow late on Sept. 3rd). Unfortunately it is not possible to take good images from earth or from HST today due to the closeness of the sun to saturn.

You might enjoy this animation http://www.avertedimagination.com/img_p ... _2006.html recorded from several shots during a single apparition of saturn. It shows the subtle changes in the shadows and ring tilt over the course of several months of observation.

Thanks very much for the comments on my APOD!

clear skies and best wishes,
Alan Friedman

[anabaptiston]

Thanks, neufer, for the wikipedia entry, but it's irrelevant. I asked if the dots were moons, and if so, could they be identified. I didn't ask how many moons Saturn had, or whether Rhea might have rings of its own. So the question still stands. (To sort of answer my own question, presumably the dots would have to be Titan or maybe Rhea is they're actually moons.)

[neufer]

Thanks, neufer, for the wikipedia entry, but it's irrelevant. I asked if the dots were moons, and if so, could they be identified. I didn't ask how many moons Saturn had, or whether Rhea might have rings of its own. So the question still stands. (To sort of answer my own question, presumably the dots would have to be Titan or maybe Rhea is they're actually moons.)

That would be my guess. The wikipedia entry is relevant; it's just not definitive.

[DavidLeodis]

I was curious how the top image showed no rings but thankfully the explanation had a link to an animation in the information to which it stated "The final frame has been assembled from earlier 2009 observations to display how the planet will appear on September 4th, 2009 when the rings will appear edge on". It would otherwise have been a very speedily produced APOD to have shown the September 4th view.

[DavidLeodis]

I was curious how the top image showed no rings but thankfully the explanation had a link to an animation in the information to which it stated "The final frame has been assembled from earlier 2009 observations to display how the planet will appear on September 4th, 2009 when the rings will appear edge on". It would otherwise have been a very speedily produced APOD to have shown the September 4th view.

Ooops I've just noticed that bystander has already mentioned about the top image.