This isn't a comet.
It's a dying star. With a tail. Its name is Mira ("the wonderful") and it's a fairly typical star. Except for that tail. It will die within the next several hundred thousand years or so.
As it burns up all its hydrogen and moves on to heavier fuels, it shakes and shudders in a series of expansions and contractions, blowing off outer layers of gas with each explosion. Death spasms. And a couple things happen. One, Mira isn't round, so these explosions are asymmetrical and send it hurtling off into space, screaming along at 80 miles a second.
Two, the outer layers of the star are blown off and left behind, which is what's forming that tail. Phil Platt over at Bad Astronomy says to "imagine running down the street with a smoke bomb in your hand." It's thirteen light years long. That's pretty big. If you look closely you can see the bow shock in front of the star, where the material the star is plowing through is building up. And the bright tendrils of material coming off the tail will eventually be folded into the creation of new stars, and new worlds, so you've got the whole life forming from death yada yada yada going on.
I wrote a novel several years ago that used the life and death of stars as an ongoing metaphor, and the crux of it was that when stars die they leave these gorgeous nebulae behind, each one complex and unique, with names like the Cat's Eye, the Ghost Head, the Tarantula, the Witch's Broom. These nebulae are around for the blink of an eye in terms of stellar lifetimes, but in that fleeting moment they shine across the heavens.
I got an Excellent Blogger award this week from Jo, who writes of color theory and takes wonderful pictures and draws little faces on her husband's toenails on April Fool's Day. Check her out. And thanks, Jo! I think blogger etiquette requires that I pass awards along to others, but I'm pretty new at this whole bloggy thing, so I feel a little weird giving awards to folks who have been doing this longer and better than I. But you know who you are. So consider yourselves awarded.