Celestia Forums

Hi all,

again Celestia is good for a stunning precision test:

Cassini's Private Eclipse:

http://saturn.jpl.nasa.gov/multimedia/images/image-details.cfm?imageID=1411

Here is some parts of the caption:

NASA wrote:For this movie, Cassini pointed its cameras toward Saturn's moon Dione to witness its distant sibling moon Rhea briefly pass behind in a series of 32 individual frames taken over 17 minutes. Four individual frames from the eclipse are shown at bottom.

Rhea (1,528 kilometers, or 949 miles across) is larger than Dione (1,118 kilometers, or 695 miles across), but also is farther away as seen here, which explains why the two moons appear to be roughly the same angular size.

I checked "Cassini's Private Eclipse" of Feb 20 2005 with Celestia and compared the result with the respective photo from the above site: amazing...



Enjoy,

Bye Fridger

I'm not sure why I can't recreate the same scene, Fridger. Looking from Cassini, I get Dione as a ball, Rhea as a bright spot to the right and Enceladus as a bright spot to the left.

Sky Pilot,

1) set UTC date to Feb 20, 12:31:00
2) type cassini, G (goto)
3) type dione, SHIFT c
4) with CTRL mouse 1 make cassini /very small/
5) with SHIFT mouse 1 zoom back in

6) look at the configuration...

There are other methods, of course.

Bye Fridger

OK, it works!! But why?

"I saw the play, but I haven't any idea how they did that." (some famous sports quote, I think)

I think I'm not understanding the dynamics of the CTRL - mouse movements. Clearly, I saw what they did, but what exactly did they do that my earlier attempt didn't do?

Also, is there a reason why Cassini's high-gain antenna isn't pointed toward Earth in Celestia?

Sky Pilot,

There currently is no functionality in Celestia which will cause an object that's following an arbitrary xyz trajectory (as Cassini does) to point toward another object at all times. My understanding is that Chris hopes to be able to add orientation coordinates to some future variation of xyz trajectories. I suspect it won't happen soon, though.

Sky Pilot wrote:OK, it works!! But why?

"I saw the play, but I haven't any idea how they did that." (some famous sports quote, I think)

I think I'm not understanding the dynamics of the CTRL - mouse movements. Clearly, I saw what they did, but what exactly did they do that my earlier attempt didn't do?

Sky Pilot,

CTRL mouse 1 changes the /real/ distance of the observer from the selected object. SHIFT mouse 1 leaves the physical distance identical, but changes the /field of view/ exactly like a telescope does. It's like magnification. This operation affects /all/ objects within the view, unlike CTRL mouse1 which only acts on the selected one! It should be easy to figure out with these specifications what's going on...

Another instructive way of getting to our configuration is as follows:

1) set the UTC date to Feb 20, 9:00, say (i.e. 30 mins earlier !)
2) type cassini, G (goto)
3) type dione, SHIFT c
4) with CTRL mouse 1 make cassini very small
5) with SHIFT mouse 1 zoom cassini and Dione to convenient sizes
......new.....
6) type ':' (lock cassini and dione!)
5) L (L) (watch the time approaching 12:31)
6) see Rhea passing and being eclipsed by Dione!

Bye Fridger

Neat! Using your < and > than can give you some really neat effects, same as with the zoom on the Cassini spacecraft.

dallas wrote:Neat! Using your < and > than can give you some really neat effects, same as with the zoom on the Cassini spacecraft.

Very cool! I didn't know it would zoom that way.

Very nice comparison Fridger - I was wondering how this might look in Celestia. I might want to try this with the latest Dione & Rhea texture that I've been working on.