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Why haven’t we seen this comet before?
I’m glad you asked, because this gives us a chance to remember just how big space is. Take our sun, for example. It’s the biggest thing in the solar system by a long shot — about 1.4 million kilometers across. That’s pretty big! But wait — the Earth is 150 million kilometers away from the Sun. You could fit more than 100 more suns in that distance, and that’s just between the Earth and the Sun on a straight line. Halley’s Comet, which is the most famous comet around, is about 15 by 8 by 8 kilometers. We’re not quite sure how big C/2012 S1 is, but you can see the difficulty here — it’s not so much “needle in a haystack” as it is “moving needle in a haystack the size of China”. Shoot, it took us until the 1600s to discover Neptune, and that thing is humongous. So, if you have C/2012 S1 coming in from the Oort Cloud, and it’s never been here before, it’s no surprise that we’re just becoming aware of it.

Why does it have that unwieldy name?
Not only is there a lot of space in … space, but there’s a lot of stuff in space. We’re not interstellar yet, but there are 400 billion stars just in our galaxy alone, and our galaxy is only one of about a half a trillion. In our solar system, we’ve got planets, planetoids, moons, comets, asteroids, and one medium-sized star in the center. The important things have names, but they share designations with the unimportant things, so you can quickly communicate information about them to those who understand the system. Let’s break C/2012 S1 down:

  • C means it’s a non-periodic comet, which is a comet that does not return to the Solar System on a regular basis, if at all. Halley’s Comet is a periodic comet because it comes around every 76 years, which means it’d be designated by the letter P.
  • 2012 is the year it was discovered. Duh.
  • S is the half-month in which it was discovered. A comet discovered in the first half of January would be labeled A. The second half would be B. The first half of February would be C, and so on. This one was discovered on September 21, and since they don’t use the letter I ‘cause it’s confusing, it’s labeled S.
  • 1 means it’s the first comet discovered in the second half of September.

See? Totally simple. If it were going to hit us, we’d probably give it a different name.

Is it going to hit us?

Are you sure?
Oh, you can never be totally sure. But yes. It’s going to pass within about two million kilometers of the Sun, but the closest it’ll get to us is about 60 million kilometers. No biggie.

How much is a kilometer again?
About six-tenths of a mile. It’s really far away! Don’t worry about it. If you’re going to worry about anything, worry about stuff that actually might kill us, like gamma-ray bursts from distant stars, or relativistic kill vehicles from paranoid alien empires, or the asteroid Apophis.

All of those things sound pretty scary!
You’re right! A gamma-ray burst would blow the atmosphere off our planet like seeds off a dandelion and irradiate us pretty badly. A relativistic kill vehicle would crack the Earth open like a walnut. Apophis would probably just look like Deep Impact, so pretty bad. We can’t do anything about the first two, so don’t worry about it, and I’ll write more about Apophis some other time, but we’ve got a long time before it might (emphasis: might) hit us, and there are a bunch of fun science-y things we could do to stop it, so don’t worry about it.

I’m still pretty worried about it.
OK then, maybe this will distract you. It’s tough to predict exactly what will happen with C/2012 S1, but you’re going to be able to see it with the naked eye in 2013, from about October to January 2014. At one point — and again, this is up in the air — it might briefly outshine the full moon. We’re going to be getting a surprise stellar show for months on end next year, and I couldn’t be happier.

This is all contingent upon the world not ending on December 21, 2012, right? Because I watched this very convincing video that–
Ugh. I’ll tell you what. If the world does end in December, I’ll give you two hundred million dollars. Deal?