What's a Meteor Shower?
The other day, Dyana copied me in on a picture post over on Google+. She requested more info about the meteor shower mentioned in it. I'm going to post the image here, but please don't automatically repost it - read what I have to say about it first!
Now, spreading the message of astronomy is something I can get on board with, but this image pops up every time there's a meteor shower approaching, and it's a bit wrong. The last time I noticed this message was just before the Perseids, which peaked around the same time as the 2012 Olympic Closing Ceremony back in August, and I'm pretty sure we'll see it again for the Leonids in November*. The image, each time, is pretty much identical down to the background image, just with the dates changed.
Ignoring the spelling and grammar issues**, here's some info about the Orionids and meteor showers in general, in the interests of polishing up the knowledge given out by such memes:
The meteor shower in question, peaking in the early morning of October 21st (for those of us in the UK), is known as the Orionids shower. Far from being "one of the rarest meteor shower[s]", the Orionids are very well known and turn up at the same time every year. This is the case with all of the most famous meteor showers, including August's Perseids, November's Leonids and December's Geminids. One of the reasons that the Orionids shower is so well known is that it's so reliable: the chances of seeing something if you look up is actually quite high, compared to non-meteor-shower nights. In fact, the wow-factor value of "about 30 meteros [sic] an hour" sounds, to me, like it has been plucked out of the air. I'd even go so far as to say that it's probably a bit low. If I was going to pluck a value out of the air*** I'd be more likely to choose about 50.
Another reason why the Orionids are pretty famous is where they come from, which is kind of the meat of this article:
The Orionids are called the Orionids because if you traced each meteor's fleeting path across the sky back the way it appears to have come, you'd find that they all seemed to come from somewhere within the constellation Orion. The Perseids, similarly, appear to originate from the constellation Perseus, the Leonids look like they come from Leo, and so on and so forth. But that's a mixture of coincidence and convenient nomenclature. Where do they actually come from?
The Orionids are bits of Halley's comet. Last seen in our region of the solar system in 1986, Halley's comet, like all comets, leaves a trail behind (and ahead) of it. Having been whirling around the solar system for possibly a couple of hundred thousand years, there's a pretty constant stream of invisible (to us on Earth) comet-debris orbiting the Sun along its path. Every year, at about the same time, Earth passes through this trail, and bits of it burn up in our atmosphere, blazing briefly across the sky as meteors.
This is where all of our annual meteor showers come from: trails of comet debris, either from active comets or the break-up of dormant comets. Some showers are heavier than others, and occasionally we get meteor storms during which we might see thousands of meteors per hour. The showers that aren't quite so regular are still predictable, but are subject to orbital changes caused by gravitational interaction with the planets of our solar system.
* There are others due before then, but they're not so well known.
** Which seem to persist with each incarnation of this meme. If you can spend the time and energy changing the date, why can't you fix 'meteros' while you're at it? Spelling and grammar are the brown M&Ms: if you can't be bothered to make sure you include an 's' when you're pluralising 'shower', then how can I possibly trust that you've done the much harder task of actually checking your facts? Please feel free to point out any grammatical or spellingular errors I've made in this post.
*** We all do it from time to time, don't we?
Ignoring the spelling and grammar issues**, here's some info about the Orionids and meteor showers in general, in the interests of polishing up the knowledge given out by such memes:
The meteor shower in question, peaking in the early morning of October 21st (for those of us in the UK), is known as the Orionids shower. Far from being "one of the rarest meteor shower[s]", the Orionids are very well known and turn up at the same time every year. This is the case with all of the most famous meteor showers, including August's Perseids, November's Leonids and December's Geminids. One of the reasons that the Orionids shower is so well known is that it's so reliable: the chances of seeing something if you look up is actually quite high, compared to non-meteor-shower nights. In fact, the wow-factor value of "about 30 meteros [sic] an hour" sounds, to me, like it has been plucked out of the air. I'd even go so far as to say that it's probably a bit low. If I was going to pluck a value out of the air*** I'd be more likely to choose about 50.
Another reason why the Orionids are pretty famous is where they come from, which is kind of the meat of this article:
The Orionids are called the Orionids because if you traced each meteor's fleeting path across the sky back the way it appears to have come, you'd find that they all seemed to come from somewhere within the constellation Orion. The Perseids, similarly, appear to originate from the constellation Perseus, the Leonids look like they come from Leo, and so on and so forth. But that's a mixture of coincidence and convenient nomenclature. Where do they actually come from?
The Orionids are bits of Halley's comet. Last seen in our region of the solar system in 1986, Halley's comet, like all comets, leaves a trail behind (and ahead) of it. Having been whirling around the solar system for possibly a couple of hundred thousand years, there's a pretty constant stream of invisible (to us on Earth) comet-debris orbiting the Sun along its path. Every year, at about the same time, Earth passes through this trail, and bits of it burn up in our atmosphere, blazing briefly across the sky as meteors.
This is where all of our annual meteor showers come from: trails of comet debris, either from active comets or the break-up of dormant comets. Some showers are heavier than others, and occasionally we get meteor storms during which we might see thousands of meteors per hour. The showers that aren't quite so regular are still predictable, but are subject to orbital changes caused by gravitational interaction with the planets of our solar system.
* There are others due before then, but they're not so well known.
** Which seem to persist with each incarnation of this meme. If you can spend the time and energy changing the date, why can't you fix 'meteros' while you're at it? Spelling and grammar are the brown M&Ms: if you can't be bothered to make sure you include an 's' when you're pluralising 'shower', then how can I possibly trust that you've done the much harder task of actually checking your facts? Please feel free to point out any grammatical or spellingular errors I've made in this post.
*** We all do it from time to time, don't we?
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