Catholic Sensibility

... is the astronomical term for one celestial body covering up another body. When I was running Cassini's Dione flyby through the solar system simulator, I noticed that the moon Rhea passed behind Dione several hours before the flyby, about 0100 Universal Time on Tuesday, in fact. NASA will get some shots of this, I thought. And they did. Check it out. These items are in the Raw Images section. The first four here were taken about 60-80 seconds apart, I'd estimate. Number five down there about four or five minutes later. If you remember vinyl records or you are a rapper, I can communicate the set up visually to you. Imagine Saturn is the metal nub around which your lp spins. The paper glued to the center of the record that tells you the song list would be the rings. Now imagine some boor at your swingin' 70's party has eaten a chocolate chip cookie while checking out your hi-fi stereo system and has left some crumbs on the vinyl. Those crumbs are Saturn's moons and if you can imagine your crummy record moving much slower than 33rpm, you'll get a feel for the occasional occultation of a moon by another. Look at your record (I hope it wasn't Pink Floyd) edge on. Every so often, that chocolate chip on track 2 will hide that cookie particle sitting on track 4 on the other side. Keep doing this for awhile, and maybe your guests will think you're dealing with some pharmaceutical you ingested. Most of Saturn's moons and all of its rings are orbiting the planet along this invisible plane. (Don't ask me about Phoebe or Hyperion right now.) From any of these "regular moons," you'd get a nice show now and then: one moon passing in front of another. Cassini scientists decided to take advantage of these occurences and get some good shots for us earthlings. This brings me to one of my beefs about set design on SF movies: when they show a nice arrangement of three or four moons in the sky of some planet. Well. Yes, it can happen. But it doesn't happen all the time. Usually, those moons would be scattered across the sky. Some of them might have set hours ago. But when they do "collide" in the sky, it's a nice sight. Two happens pretty frequently, at least from the viewpoint of Cassini. As you can see, it doesn't last for too long. I'm waiting for some confluence of three moons. If I had a day to burn, I'd run the solar system simulator and see if anything was coming up. Meanwhile, if any celestial events happen by your way today, be sure to look up.