I know I haven't been posting much astronomy the past few days -- Comic Con, w00tstock, and "Bad Universe" have kept me hopping -- so to make up for it a little bit, here's a lovely image sent back a billion kilometers from Cassini:
This is Tethys, an ice moon of Saturn. The angle of Cassini, Tethys, and the Sun light the moon as a crescent. The most obvious feature is Ithaca Chasma, a (more than) thousand-kilometer-long gash in the side of the object. Note that Tethys is only about 1000 km in diameter, so the chasm runs along a third of the moon's surface (circumference = diameter x π, remember). How big is that? Stand up and take a long stride. That's about one meter. Now do it 999,999 more times. That's a megameter: a million meters, or 1000 kilometers. Better pack a lunch. The chasm is billions of ...
