APOD and General Astronomy Discussion Forum
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Your understanding of the physics is correct (I'd say it a little differently, that the orbit radius is a function of orbital speed). The reason that Prometheus has a greater orbital speed than the F-ring is because it is closer to Saturn. In fact, the inner F-ring is orbiting faster than the outer F-ring.Tino wrote:Even though Prometheus is vastly larger than the particles that make up the F-ring I don't understand how it is that they orbit at different speeds. I thought that orbital speed was a function of altitude but not mass. Can somebody explain this to me? Thanks in advance.
Thanks for your answer Chris. Do you happen to know if the 15 hour period between Prometheus' forays into the edge of the F-ring are regular intersections of its elliptical orbit, or is it something else?Chris Peterson wrote: Your understanding of the physics is correct (I'd say it a little differently, that the orbit radius is a function of orbital speed). The reason that Prometheus has a greater orbital speed than the F-ring is because it is closer to Saturn. In fact, the inner F-ring is orbiting faster than the outer F-ring.
So I would assume. Prometheus has an orbital period of .613 days (14.7 hours), and an orbital eccentricity of 0.003.Tino wrote:Thanks for your answer Chris. Do you happen to know if the 15 hour period between Prometheus' forays into the edge of the F-ring are regular intersections of its elliptical orbit, or is it something else?
In this contrast stretched image, you're mainly seeing a silhouette and a shadow. The actual shape of the moon is more like a potato. It's a "moon" because it orbits Saturn, but it's far too small to settle into a spherical shape. If it were in orbit only around the Sun, we'd consider it nothing more than a medium sized asteroid.Umbobo wrote:So, am I to understand the cornflake shaped entity in the upper left of this APOD frame is indeed the moon Prometheus? Pretty bizarre shape.
Actually, I've read it's mostly ice. If so, it probably came from the outer reaches somewhere, and if it were passing through the inner system we consider it a comet. Not necessarily, though. There's a lot of overlap between what we call asteroids and what we call comets- particularly if the comets have been heated enough to lose most of their ice.Frenchy wrote:If Prometheus is an asteroid type body, does this mean that it originated from the asteroid or Kuiper belt? (I'm not sure of scale of distances of both from Saturn)
For scale, If you were traveling from the Sun outward to Pluto's mean distance,You would reach the 1/2 way point after you passed Uranus.Frenchy wrote:If Prometheus is an asteroid type body, does this mean that it originated from the asteroid or Kuiper belt? (I'm not sure of scale of distances of both from Saturn)
http://en.wikipedia.org/wiki/Prometheus' wrote:
<<Prometheus (Ancient Greek: Προμηθεύς, "forethought") was a champion of human-kind known for his wily intelligence, who stole fire from Zeus and gave it to mortals. Zeus then punished him for his crime by having him chained to a Rock(efeller Center) in the Caucasus, while a great eagle ate his liver every (15 hour) day only to have it grow back to be eaten again the next day. Years later the Greek hero Heracles (Hercules) would shoot the vulture and free Prometheus from his chains.>>
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Prometheus Orbital period: 14.71 hours
Prometheus Rotation period: synchronoushttp://apod.nasa.gov/apod/ap090427.html wrote:
Explanation: <<Prometheus orbits Saturn just inside the thin F-ring, but ventures into its inner edge about every 15 hours. Prometheus' gravity then pulls the closest ring particles toward the 100-km moon. The result is not only a stream of bright ring particles but also a dark ribbon where ring particles used to be. Since Prometheus orbits faster than the ring particles, the icy moon pulls out a new streamer every pass.>>
I'm not sure that's a good idea. It would make the bottles rather heavy and unwieldy.aristarchusinexile wrote:How do I go about getting permission to use that stuatue on the label?
Okay, how about paper mache copies? Or, talking relatively, putting it on a very BIG bottle where its weight would be small in comparison to the bottle and contents .. a bottle suited for someone trying to wade through daily life on this planet.bystander wrote:I'm not sure that's a good idea. It would make the bottles rather heavy and unwieldy.aristarchusinexile wrote:How do I go about getting permission to use that stuatue on the label?
The 5-mile-wide (8-kilometer) moon Daphnis orbits within the 26-mile-wide (42-kilometer) Keeler Gap in Saturn's outer A ring, and its gravitational pull perturbs the orbits of the particles forming the gap's edges. The eccentricity, or the elliptical deviation from a circular path, of Daphnis' orbit can bring it close to the gap edges. There, its gravity causes larger effects on ring particles than when it is farther away. Previous Cassini images have shown that as a consequence the moon's effects can be time-variable and lead to the waves caused by Daphnis to change in shape with time and with distance from the moon.
However, the new analysis also illustrates that when such a moon has an orbit inclined to the ring plane, as does Daphnis, the time-variable edge waves also have a vertical component to them. This result is backed by new images taken recently near equinox that show the shadows of the vertical waves created by Daphnis and cast onto the nearby ring match the characteristics predicted by the new research.