Saturnian moons mutual events

Calculus · Post #1by **Calculus** » 13.11.2002, 21:00

The saturnian mutual events (eclipses and occultations of saturn's satellites) occur every 13-16 years. Last times were in 1979/1980 and 1996/1997. Next time is in 2009.
I am pleased to say that Celestia simulates correctly these events (except for the light speed delay).
(Only Jupiter's and Pluto's mutual events are to be fixed).

Calculus · Post #2by **Calculus** » 13.11.2002, 21:05

My graphic card doesn't allow me to see the ring's shadows.
Could someone tell me if the rings shadow eclipses saturn's moons (in Celestia)?
And does saturn's moons cast a shadow on the rings (in Celestia)?

Post #3by **chris** » 13.11.2002, 21:35

Calculus wrote:My graphic card doesn't allow me to see the ring's shadows.
Could someone tell me if the rings shadow eclipses saturn's moons (in Celestia)?
And does saturn's moons cast a shadow on the rings (in Celestia)?

No shadows are cast from rings to moons or from moons to rings. This would be a good thing to fix for the future; do you links to any images of such phenomena?

--Chris

Post #4by **selden** » 13.11.2002, 22:46

It seems to me that there are two possible cases of moon shadows cast onto the rings:

a) Shadows cast across the rings by those moons which orbit in the plane of the rings. These events would only happen at the time of the Saturnian year when the rings are edge-on to the sun and thus edge-on when seen from the Earth. Such shadows would be *extremely* difficult for us to observe, since the rings are effectively invisible when edge-on. We can hope that Cassini might see some, though.

b) shadows cast up (or down) onto the rings at other times of the Saturnian year by moons which have inclined orbits, namely Iapetus and Phoebe. Those moons are tiny and way far out, so the probabllity of seeing one of these events in our lifetimes is miniscule. I haven't done the math, but I'm sure that their umbras don't reach that far, either. (i.e. you'd be watching a transit of the sun by the moon, not an eclipse).

All the more reason for Celestia to be able to show us type a !

Calculus · Post #5by **Calculus** » 14.11.2002, 00:14

There is of course no images of moons eclipsed by the rings' shadow or the ring itself.
A shadow casted by a moon on the rings is actually a very rare phenomenon to observe in good condition. There has been only one observation recorded in 1996. It was during the eclipse of Mimas by Titan. During the event the two shadows were observed to transit over the rings of Saturn. No picture, only astrometric data.
Iapetus can more easily cast a shadow on the rings but I have never heard of any observation. But you can make a simulation with celestia. Set the date to dec 22,1980 and look at Iapetus shadow crossing saturn (and the rings).

Calculus · Post #6by **Calculus** » 14.11.2002, 00:45

b) shadows cast up (or down) onto the rings at other times of the Saturnian year by moons which have inclined orbits, namely Iapetus and Phoebe. Those moons are tiny and way far out, so the probabllity of seeing one of these events in our lifetimes is miniscule. I haven't done the math, but I'm sure that their umbras don't reach that far, either.

Actually, Iapetus is big enough (radius 718km) to cast a shadow.
I've added a picture in my gallery where you can see the shadow thru the Cassini division of the rings.

Post #7by **selden** » 14.11.2002, 02:37

Calculus,

Thanks!

Now Chris is going to have sweat just a little more blood to make shadow casting even more general

Post #8by **selden** » 14.11.2002, 03:17

Paul,

Well while the shadow isn't on the rings, at least it's in the shadow of the rings

I've added my own view of it to my own gallery at http://www.lns.cornell.edu/~seb/celestia/gallery-001.html#11
(with appropriate credit)

Post #9by **selden** » 14.11.2002, 03:37

I found a picture of the F ring shadow cast on Epimephius.
See http://www.physics.usyd.edu.au/~ptitze/aa/saturn_sats.html

It really brings home just how thin the rings are. Now if only we could bring it home using Celestia

Calculus · Post #10by **Calculus** » 14.11.2002, 03:57

I wish I had the hardware to see the rings shadows (or Chris worked more on Radeon)

HankR · Post #11by **HankR** » 20.01.2003, 22:55

I found a nice transit of Iapetus' shadow on Saturn on 5 Oct 2022. Iapetus is very interesting to visit. Because of the inclination of its orbit, it has better views of Saturn's rings than can be seen from the equatorial moons. Also, its surface coloration is very unusual. Give it a look.

- Hank

Post #12by **selden** » 21.03.2003, 14:06

It seems that the orbits of Saturn's moons as calculated by Celestia have changed since we first did this.

I've been trying to reproduce the 1980 Iapetus eclipse using Celestia v1.3pre3 and have not been able to do so. The configuation of the moons at the time (1980-12-22 02:48:05) is now quite different from when I originally generated my picture of the shadow of Iapetus within the shadow of the rings.

Paul, did you determine the time of the eclipse from "first principles" or did you find it by watching Celestia?

I've found a Web page that mentions that there should be several Iapetus eclipses in 1992, but I haven't had time to track down the details.

See http://www.bdl.fr/Phemu03/ntph07.html

Post #13by **chris** » 21.03.2003, 17:03

selden wrote:It seems that the orbits of Saturn's moons as calculated by Celestia have changed since we first did this.

I did adjust the orbits to be (I thought) more accurate . . . But something still seems fishy. I need to do some more tests against Horizons data. A complication is that there are differences between the position of Saturn from Horizons and the VSOP87 series calculations. I spent quite a bit of time tracking down errors in the positions of the Uranian satellites that turned out to be almost exclusively due to error in the position of Uranus itself. The VSOP87 series give arcsecond accuracy, but an arcsec is long distance at 20 au.

--Chris

Post #14by **selden** » 21.03.2003, 17:36

I found the original predictions for the transits of Saturn by Iapetus (published in 1992 for 1993). The paper is at http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1992A%26A...265L..21S&data_type=PDF_HIGH&type=PRINTER&ext=.pdf

The transits were to take place May 1-2 and July 20-21, 1993.

Unfortunately, Celestia shows Iapetus missing Saturn.

So far I haven't found any actual records of the transits, though.

Calculus · Post #15by **Calculus** » 22.03.2003, 20:26

selden wrote:It seems that the orbits of Saturn's moons as calculated by Celestia have changed since we first did this.

I've been trying to reproduce the 1980 Iapetus eclipse using Celestia v1.3pre3 and have not been able to do so. The configuation of the moons at the time (1980-12-22 02:48:05) is now quite different from when I originally generated my picture of the shadow of Iapetus within the shadow of the rings.

Paul, did you determine the time of the eclipse from "first principles" or did you find it by watching Celestia?

I've found a Web page that mentions that there should be several Iapetus eclipses in 1992, but I haven't had time to track down the details.

See http://www.bdl.fr/Phemu03/ntph07.html

I tried to reproduce it and couldn't do it either.

If I remember well, I found the Iapetus eclipse information somewhere on the Internet. But I don't remember where (most likely from the bdl site). However, the images of Saturnian Satellites mutual events I posted, are accurate with respect to BDL information (except for the light time delay). Though they don't involve Iapetus.

The image of the 12 best Saturnian Satelittes Mutual Events as seen from earth for the period 1995-1996 is here
http://ennui.shatters.net/gallery/view_photo.php?set_albumName=Calculus&id=12_Saturnian_Mutual_Events_1995_1996_V2