Celestia Forums

Here is a nice event in the Saturnian system, predicted by Celestia for April 7, 2009

A solar eclipse for observers located on Enceladus! The body eclipsing the Sun is the moon Mimas.

Have a look:
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In the first image below, we are located in space just behind Enceladus, watching Mimas shortly before covering the Sun. You see the dark edge of Enceladus on the right of the image.



In the next image we have moved towards Mimas, which is easy to recognize...




Finally we look 180 degrees back onto the "would-be" illuminated side of Enceladus, and notice the very extended annular eclipse shadow, cast by Mimas in front of the Sun...



If someone can dig out an accurate, calculational prediction of this event from the net, it could serve as another challenging test for Celestia's accuracy...

Enjoy,
Fridger

Nice find!

Here's a list of satellite events during Saturn's 2009 equinox:

ftp://cdsarc.u-strasbg.fr/pub/cats/J/A+A/485/293/ReadMe
ftp://cdsarc.u-strasbg.fr/pub/cats/J/A+ ... tab4-7.dat

And here's the record for your eclipse:


The time is different, but I'm pretty sure that the table gives the time of the event as seen from Earth. It also uses TT instead of UTC, for an extra 66 seconds of difference. It would be interesting to compare the timings from the built-in orbits of the Saturnians with those from volcanopele's SPICE solar system add-on.

--Chris

chris wrote:Nice find!

Here's a list of satellite events during Saturn's 2009 equinox:

ftp://cdsarc.u-strasbg.fr/pub/cats/J/A+A/485/293/ReadMe
ftp://cdsarc.u-strasbg.fr/pub/cats/J/A+ ... tab4-7.dat

And here's the record for your eclipse:

Code: Select all

2009/04/07 1E2 A  6: 8:43  6: 9: 2           6: 9:47  6: 9:58           6:10:32  6:10:51  .465  .465   .679   .632  128  129 2.9 .014 .017


The time is different, but I'm pretty sure that the table gives the time of the event as seen from Earth. It also uses TT instead of UTC, for an extra 66 seconds of difference. It would be interesting to compare the timings from the built-in orbits of the Saturnians with those from volcanopele's SPICE solar system add-on.

--Chris

Oh, thanks Chris, I knew that you had those references from your earlier tests .

Now, perhaps you have forgotten how to apply my LT feature: activate it and select Earth, while being close to Enceladus and the eclipse being maximal:

This happens 4:47 local UTC time and after switching on LT, I read off 6:8:45 UTC for Earth, in amazingly good agreement with your above data!!



In detail:

Adding 66" to convert UTC to terestial time (TT) gives 6:9:51 TT for the maximum according to Celestia!! From your table, the average between the two quoted maximum predictions is 6: 9:52.5 TT ... Wow...

Fridger

t00fri wrote:Oh, thanks Chris, I knew that you had those references from your earlier tests .

Now, perhaps you have forgotten how to apply my LT feature: activate it and select Earth, while being close to Enceladus and the eclipse being maximal:

This happens 4:47 local UTC time and after switching on LT, I read off 6:8:45 UTC for Earth, in amazingly good agreement with your above data!!

In detail:

Adding 66" to convert UTC to terestial time (TT) gives 6:9:51 TT for the maximum according to Celestia!! From your table, the average between the two quoted maximum predictions is 6: 9:52.5 TT ... Wow...

Very good to see that the agreement is so close once light time and the TT-UTC difference have been accounted for. The light time feature is indeed useful in these situations. Celestia might also benefit from an option to show the time as TT (or TDB, which is very close to TT.)

One thing that I don't understand: the table lists this even as an annular eclipse, yet Mimas occludes the Sun completely. The apparent size of Mimas is almost three times that of the Sun during the event.

EDIT: Just figured this out (I think)... Annular in this context means that the shadow of Mimas doesn't completely cover Enceladus.

--Chris

chris wrote:...
One thing that I don't understand: the table lists this even as an annular eclipse, yet Mimas occludes the Sun completely. The apparent size of Mimas is almost three times that of the Sun during the event.

EDIT: Just figured this out (I think)... Annular in this context means that the shadow of Mimas doesn't completely cover Enceladus.

--Chris

Yes, Chris,

that's the understanding in the language of "mutual events" : annular refers to the "uneclipsed" fraction on the eclipsed body (r_shadow < r_body). In solar eclipses on Earth it's actually different: an annular solar eclipse means that the apparent size of the Moon is smaller than that of the Sun. Hence the Sun appears as a very bright ring, or annulus, surrounding the outline of the Moon.


(from NASA)

Fridger

Chris,

did you ever see this amazing annular solar eclipse ? (NASA STEREO-B spacecraft)

Single image from video:
------------------------------
http://upload.wikimedia.org/wikipedia/c ... -B.ogg.jpg

Great OGG Video of Moon's passage (VLC player!):
---------------------------------------------------------------------------
http://upload.wikimedia.org/wikipedia/c ... EREO-B.ogg

Fridger

...and as a by-product, this interesting constellation shortly after the Enceladus eclipse:
The observer is also located on Enceladus:



Fridger

t00fri wrote:Great OGG Video of Moon's passage (VLC player!):
---------------------------------------------------------------------------
http://upload.wikimedia.org/wikipedia/c ... EREO-B.ogg

I've seen this video before, but it's worth revisiting. Spectacular!

--Chris

On April 22, Mimas and Enceladus do it again:

Celestia URL