by neufer » Wed Sep 22, 2021 9:26 pm
MarkBour wrote: ↑Tue Sep 21, 2021 8:10 pm
- Does this show the greatest angle at which we ever see the rings (from Earth)? I've never seen them tilted further than the end images shown, but I've not been observing Saturn for very long.
- It looks like the images toward the middle sometimes show a noticeable black edge to the rings as they cross the planet's disk. I'm guessing this is not really the rings themselves, but their shadow on the cloud tops of Saturn, making what looks like a black stroke there. Is that right?
- If Saturn were to turn so that the rings were completely sideways (so that Saturn's equatorial plane was perpendicular to our line of sight) would they perhaps appear fainter, rather than as bright and glorious as in these images? I'm thinking that they are so thin that they might have more transparency and not reflect as much light per pixel as they do when seen at an angle. They would still certainly reflect at least as much light in total, but it would be spread over a larger area, so it seems they could actually dim somewhat. (I assume analysis of some Cassini images could answer this question, but I'm just asking it, I'm too lazy to go work on that ...)
From Earth the (penumbra) ring shadow is
always thicker than the (brighter) rings:
https://apod.nasa.gov/apod/ap110308.html wrote:
Explanation: How thin are the rings of Saturn? Brightness measurements from different angles have shown Saturn's rings to be about one kilometer thick, making them many times thinner, in relative proportion, than a razor blade. This thinness sometimes appears in dramatic fashion during an image taken
in infrared light.
Note, however, that the ring can be
quite dark from the side in violet-light images:
- This probably implies that the "one kilometer thick" ice ring
is shrouded in in a much thicker (100 km?) dust ring:
https://apod.nasa.gov/apod/ap040712.html wrote:
Explanation: What are Saturn's rings made of? This and other images show that inner rings have more dirt than outer rings. Specifically, as shown above, the thin rings in the Cassini Division on the left have relatively high dirt content compared to the outer parts of Saturn's A ring.
The "outer parts of Saturn's A ring" is, indeed,
quite bright beyond the Keeler Gap:
Perhaps, thanks to Daphnis and its waves,:
- "some of Saturn's ring particles temporarily collide, effectively
recycling ring particles by bringing fresh bright ices to the surface":
https://apod.nasa.gov/apod/ap120916.html wrote:
Explanation:
Some of Saturn's ring particles temporarily bunch and collide, effectively recycling ring particles by bringing fresh bright ices to the surface. Seen here, Saturn's rings were imaged in their true colors by the robotic Cassini in late October.
https://en.wikipedia.org/wiki/Rings_of_Saturn#Keeler_Gap wrote:
Near Saturn's equinox, Daphnis and its waves cast shadows on the A Ring.
<<The Keeler Gap is a 42-km-wide gap in the A ring, approximately 250 km from the ring's outer edge. The small moon Daphnis, discovered 1 May 2005, orbits within it, keeping it clear. The moon's passage induces waves in the edges of the gap (this is also influenced by its slight orbital eccentricity). Because the orbit of Daphnis is slightly inclined to the ring plane, the waves have a component that is perpendicular to the ring plane, reaching a distance of 1500 m "above" the plane.>>
[quote=MarkBour post_id=316883 time=1632255006 user_id=141361]
[list=1]
[*]Does this show the greatest angle at which we ever see the rings (from Earth)? I've never seen them tilted further than the end images shown, but I've not been observing Saturn for very long.
[*] It looks like the images toward the middle sometimes show a noticeable black edge to the rings as they cross the planet's disk. I'm guessing this is not really the rings themselves, but their shadow on the cloud tops of Saturn, making what looks like a black stroke there. Is that right?
[*] If Saturn were to turn so that the rings were completely sideways (so that Saturn's equatorial plane was perpendicular to our line of sight) would they perhaps appear fainter, rather than as bright and glorious as in these images? I'm thinking that they are so thin that they might have more transparency and not reflect as much light per pixel as they do when seen at an angle. They would still certainly reflect at least as much light in total, but it would be spread over a larger area, so it seems they [i]could[/i] actually dim somewhat. (I assume analysis of some Cassini images could answer this question, but I'm just asking it, I'm too lazy to go work on that ...)[/list][/quote]
From Earth the (penumbra) ring shadow is [u]always[/u] thicker than the (brighter) rings:
[quote=https://apod.nasa.gov/apod/ap110308.html]
Explanation: How thin are the rings of Saturn? Brightness measurements from different angles have shown Saturn's rings to be about one kilometer thick, making them many times thinner, in relative proportion, than a razor blade. This thinness sometimes appears in dramatic fashion during an image taken [b][u][color=#FF0000]in infrared light[/color][/u][/b].[/quote]
Note, however, that the ring can be [b][u]quite dark from the side [color=#FF00FF]in violet-light images[/color][/u]:[/b]
[quote=https://apod.nasa.gov/apod/ap180402.html]
Explanation: [b][u][color=#FF00FF]The violet-light image[/color][/u][/b].[/quote]
[list]This [color=#0000FF]probably[/color] implies that the "[b][i][color=#0000FF]one kilometer thick[/color][/i][/b]" ice ring
is shrouded in [b][u]in a much thicker (100 km?) [color=#FF0000]dust ring[/color][/u][/b]:[/list]
[quote=https://apod.nasa.gov/apod/ap040712.html]
Explanation: What are Saturn's rings made of? This and other images show that inner rings have more dirt than outer rings. Specifically, as shown above, the thin rings in the Cassini Division on the left have relatively high dirt content compared to the outer parts of Saturn's A ring.[/quote]
The "outer parts of Saturn's A ring" is, indeed, [u]quite bright beyond the Keeler Gap[/u]:
[list]https://apod.nasa.gov/apod/ap111012.html[/list]
[quote=https://apod.nasa.gov/apod/ap200527.html]
Explanation: The featured image is Saturn's A ring, with the broad Encke Gap on the far right and the narrower Keeler Gap toward the center.
https://apod.nasa.gov/apod/ap191012.html
https://apod.nasa.gov/apod/ap151203.html[/quote]
[b]Perhaps, [url=https://apod.nasa.gov/apod/ap191103.html]thanks to Daphnis and its waves[/url],:
[list]"[i][color=#0000FF]some of Saturn's ring particles temporarily collide, effectively
recycling ring particles by bringing fresh bright ices to the surface[/color][/i]":[/b][/list]
[quote=https://apod.nasa.gov/apod/ap120916.html]
Explanation: [b][color=#0000FF]Some of Saturn's ring particles temporarily bunch and collide, effectively recycling ring particles by bringing fresh bright ices to the surface.[/color] Seen here, Saturn's rings were imaged in their true colors by the robotic Cassini in late October.[/b][/quote]
[quote=https://en.wikipedia.org/wiki/Rings_of_Saturn#Keeler_Gap]
[float=left][img3=""]https://upload.wikimedia.org/wikipedia/commons/7/7f/Daphnis_edge_wave_shadows.jpg[/img3][/float]
:arrow: Near Saturn's equinox, Daphnis and its waves cast shadows on the A Ring.
<<The Keeler Gap is a 42-km-wide gap in the A ring, approximately 250 km from the ring's outer edge. The small moon Daphnis, discovered 1 May 2005, orbits within it, keeping it clear. The moon's passage induces waves in the edges of the gap (this is also influenced by its slight orbital eccentricity). Because the orbit of Daphnis is slightly inclined to the ring plane, the waves have a component that is perpendicular to the ring plane, reaching a distance of 1500 m "above" the plane.>>[/quote]