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 years old, and may have formed when water inside the moon froze, expanded, and cracked the surface open. It's a hundred kilometers across and 3-5 km deep, too. It's far larger than the Grand Canyon, the largest canyon on Earth.
Space is big, and weird, where even small objects have huge features. It's surprising, but surprising things are the best things to know.
Tip o' the dew shield to Carolyn Porco.