Hola,
After I posted that devastating portrayal of the state of the ‘average person’s’ knowledge of our cosmos last week. I figured I’d write a post or two regarding just what lurks out and about in our stellar neighborhood and what it actually is. That way, should you ever get stopped by Jay Leno on the street and asked what a comet is, you won’t be forced to tell him that it’s ‘A star that, due to physics, has had its barometric pressure rise and causes it to spin’.*
So, I’ve been excited for the possibility that Comet Ison will be viewable this fall, now, I don’t want to get too excited, because folks in the know aren’t sure what to expect. But the most optimistic predictions say it will be as bright as the full moon and easily viewable even in the middle of the day. It would be, without a doubt, the brightest comet as viewed from earth in over a century.
Think of it, almost no one alive would have ever had the opportunity to see a comparable celestial event.
Oh, the number of people that think that the comet will get that bright are getting smaller daily. The latest observations make folks think that if it doesn’t get so close to the sun that it breaks up, then it still won’t get as bright as those early reports indicated. Which would suck. Hard. Regardless, I’m following the story as close as I can, and the comet should still be viewable to the naked eye in December or so even if it is a bit of a dud (assuming it survives its close encounter with the sun). Its problem is that it’s too damn small.
Okay, you know how in space no one can hear you scream? That’s because there is no atmosphere to propagate the variations in air pressure that an ear drum can detect and interpret as a sound – let alone a scream. It’s called a vacuum. Another intrinsic property of a vacuum is that liquid water can’t exist in a vacuum (no one call me on that, it CAN, just not for long enough for it to be meaningful**). So way out in space, if you find water, it will be in the form of ice.
Comets tend to live waaaay out on the outskirts of the solar system. Where temperatures are close enough to absolute 0 (which is minus 459-ish Fahrenheit) that a few degrees here are there are meaningless… comets start out near the orbit of Pluto in the Kuiper Belt, where things like Halley’s comet live, and go all the way out into something called the Oort Cloud, which extends out a light-year or so from the sun.
And it’s from the Oort cloud, Comet Ison comes, it’s either a long period comet (something that has an orbital period that could be many thousands of years, where most of its time is spent on the outer reaches of the solar system), or something deep in the darkness between the stars gave it a nudge in our general direction.
And it is barreling towards the sun.*** At this point, I would point out here a couple of things, one, comets are not asteroids. Comets are made of different stuff, they’re, for all practical purposes, giant iceballs (with other stuff in them). Asteroids are rocks (which are subcategorized further, but that’s another discussion for another day). Of course, as you move out into the colder portions of the solar system, the transition from asteroids to comets is a slow one, and there are some that are rocks with Ice, and others that are Ice with rocks mixed in (called Centaurs, of course)… so, in the middle it can get fuzzy trying to categorize them, but like most things, the extremes tend to be easy to tell apart.
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You really need to click and look at this pic. NASA put together this image.
It shows all the asteroids they've been tracking that have orbits intersecting earth's.
ZERO comets are pictured here. ZERO! |
My second point, which relates to what I mentioned earlier about liquid water not being able to exist in space, is that once a comet gets close enough to the sun for the ice to melt, it goes straight from ice to gas. The process is called sublimation. And when a comet comes barreling towards the sun, all that ice begins to get turned straight into vapor – it forms a gassy atmosphere (called a coma) and then solar radiation starts blowing it away.
And then we get that tail of the comet that we all love to see (Actually, it’s not technically a ‘comet’ unless it has that tail, but, whatever – categorizing celestial bodies in astronomy is a very contentious thing, I’m just trying to keep it simple). Those tails can stretch out for millions of miles and become quite bright.****
Comet Ison is going to get very close to the sun. This is probably its first trip here (based on some other evidence that I won’t get into) and it may fizzle in an epic destruction that we won’t be able to see (because it would require staring at the sun… not easy to do). So I’ve been keeping my fingers crossed that it’s going to be epic AND viewable. Keep your eyes peeled.
Oh, and if you’re ever stopped by Jay Leno and he asks about comets… give him hell.
Okay, one more thing, as a final note here to the main post (not a footnote, which there are several)… like most things, I don’t actually look things up for the purposes of a post, research wise. So, there is a small chance that I’ve made some ‘technical’ errors above. So don’t cite me as a source if you’re trying to settle a bet or something. I’m just shooting from the hip here. Also, don’t give me grief because I didn’t explain this one thing you think I should have, there is a LOT of stuff I could have put in, but didn’t in an effort to make this post less than a book length.
*That’s so wrong that just calling it wrong, feels, well, wrong. It starts wrong from the first time that man said a noun, then got increasingly wronger from there. If you didn’t see the video, it was in my post from last week. Seriously, wow.
** There was an incident at a NASA training facility and an astronaut had a suit malfunction when being put in a vacuum chamber… before he passed out he recalled that the moisture in his mouth began boiling away. Seriously, no liquid water in a vacuum.
*** Comets tend to travel much faster that asteroids btw, so the kinetic energy of one hitting the earth is much greater considering its mass. So the distinction is important to make if you hear someone say that it’s a comet heading our way, we’re probably going to be screwed. We wouldn’t have that much notice anyway (Remember? Asteroids tend to be much closer to the sun than comets are, and orbit the sun in a way we can track them much better). So any comet on a collision course with earth would be traveling 100,000 mph or so… considering how big those things can be… we’d all be dead.
****I don’t know how to make those awesome cross looking things for my footnotes, but I sure wish I could. Anyway, comet tails always, ALWAYS point away from the sun, no matter which direction it is moving, so once a comet makes its closest pass of the sun and begins moving back out to the deep parts of the solar system, that tail will still be pointing away from the sun, it can make you think it’s moving backwards.
