Comet me bro
2016 update: funny how unpredictable comets are. Fun to look back at this and see how far off some of it was.
You are probably aware that it is the year 2013 and possibly aware that comets are a thing, but you may not know just how cometous* this year is going to be. When I was a kid, we were told that the 1986 visit from Halley’s Comet would be the one great comet we would ever get to see in our lifetimes. This was the first time in my young life I was ever given something concrete against which to measure my own mortality. I was kind of bummed about it at the time. We knew it wouldn’t return until 2061, but it freaked me out to see I date on paper I might not see in life. The good news now is that all those jerks were wrong! Well, about the comet anyway.
I suppose that this post deserves a short reminder of where comets come from first, so here we go. I’ll try to keep it simple.
There are a LOT of comets. BILLIONS of them. Probably.
Of all the things in space that have names, my favorite name of a thing is the “Termination Shock“, which represents one of the main boundaries of our sun’s influence. Beyond (and within) this boundary lies my second favoritely names space thing: The Oort Cloud. This is were the comets live and while theoretical, it’s generally accepted that it’s out there. Since comets aren’t that big (it varies, but probably not much bigger than 20 miles across at most), they’re orbiting at a great distance (WAY beyond the orbit of Pluto) and the region we’re talking about is friggin’ enormous, we can’t directly observe them. Even several billion comets forming the cloud isn’t enough to make it seem much more than very tenuously populated. Space is really a very big place, even within/around our solar system.
Every once in a while, however, one of these comets’ eccentric orbit brings it a bit closer to the sun and becomes more noticeable. If you’ve heard about comets before, you’ve probably heard the term “dirty snowball” used to describe them, which pretty much sums it up, if you make your snowballs out of dust, bit of rock, methane and ammonia. I know I do.
As the comet is warmed by the sun, some of the components of the comet start to liven up, vaporize and vent out into a cloud (coma) around the core of the comet (nucleus), which can then be blasted away by the solar wind to form a tail, which is what we typically think about when we envision a comet. Because this is how the tails form, the tail will always point away from the sun and not simply trail behind it as it moves through space, which can go against our intuition.
All of this leads to comets being discovered when they get close enough to become visible. Some (like Halley’s) do this for us regularly, as dictated by their orbits. The tricky thing is that the orbital periods of other comets are horrendously long. The smaller orbited ones we call “short period” comets and their orbits take less than 200 years. Halley’s Comet (at 75 years) is on the quick end of this scale, the furthest it gets from the sun (aphelion) being a bit past Neptune. “Long period” comets can have orbits that take thousands years, but can easily be hundreds of thousands or even millions of years. This means there are likely comets that were visible from Earth before there were any humans to see it and won’t be back until long after we’ve been eradicated or enslaved by our robot overlords.
But for now, we know of two that promise to put on a show for us this year. The first is called PanSTARRS (or C/2011 L4) and will be visible to the northern hemisphere next month. If you live in the southern hemisphere and have binoculars or a small telescope, you can see it now, but here in New England, we’re going to have to wait until the latter half of March. Currently there’s some debate about just how visible it’s going to be, but it’s probably going to be the kind of thing you’ll notice just after sunset and think is pretty neat, but nothing that is likely to create panic in the streets.
Comet ISON is likely to cause panic in the streets. It will possibly be brighter than the full moon, maybe even bright enough to read by, and it’s tail might fill a decent portion of the night sky. That’s VERY bright and this will be an unforgettable sight. It’s worth noting that this Halley-buster was only discovered last year on 9/21. There’s no way to know for sure exactly how big or bright this comet will appear for sure, but we know it’s going to be pretty damn impressive. I’d tell you to keep an eye out for it next winter, but I seriously doubt you’ll miss it.
This has the real possibility to be the brightest comet we see in our depressingly short lifetimes, but who knows, maybe it won’t be as bright as we hope or maybe something even grander will come along. Or maybe we will figure out how to transfer our consciousnesses into machine bodies that are immortal and WE can be the robot overlords.
*My first made-up word this year! It means “full of comets”.
When I was writing this post, I knew there was a third comet to mention for this year, but I couldn’t remember what it was called and there hasn’t been too much written about it, but ONE day after I published this, I found it.
Comet Lemmon (c/2012 f6) was discovered last March by the Mt. Lemmon Sky Survey in Arizona and will be visible in Northern Hemisphere skies in April, so we could have another good one this spring.