Astronomy Cast Ep. 8: Meteor Showers. Yes, the Sky is Falling!

What actually causes meteor showers

0:00It's the 365 Days of Astronomy podcast, coming in 3, 2, 1.

0:30Astronomy cast episode 8 for Monday, October 30th, 2006. Meteor showers. Yes, the sky is falling. Welcome to Astronomy cast, our weekly facts-based journey through the cosmos. It's our goal to help you understand not only what we know, but how we know what we know. My name is Fraser Cain, and I'm the publisher of Universe Today, and with me is Dr. Pamela Gay, a professor at Southern Illinois University, Edwardsville. Hi, Pamela. Hey, Fraser. How are you doing? Very well. All right. I'm looking forward to this show. This is like one of my favorite topics. So before I get to that

1:04though, so you can send us any questions, comments, or feedback to info at astronomy cast, and you can visit our site at astronomycast.com. You can give us feedback on every show. There's a link to the forum on every episode. And if you'd like to suggest a show idea, that would be great. We've got a thread in the forum for that too. So last week we talked about how to get involved in amateur astronomy. You all had some homework, so I'm hoping that you've had a chance to send in some email. And if not, please do. Let us know how you're getting involved in amateur astronomy. It's been working

1:37out for you so far, what you've seen. Now, on to another favorite event in astronomy, and this is meteor showers. Now, most people, I think, totally overestimate what they're seeing when they're watching a meteor shower. I think they're kind of imagining some kind of rain of giant space rocks crashing through the atmosphere, but that's not really what's going on, is it, Pamela? No, we're actually basically getting handfuls of dirt thrown at us by comets. As comets go through the inner parts of the solar system, the sun heats them up and they melt. And as they melt, they don't

2:14go into a liquid form. They actually go straight from solid to gas. And the gas carries with it bits of dirt and dust that the comet has picked up as it's gone through the solar system. And if the Earth crosses the path of one of these comets, we intercept this dust and dirt. And when it hits our atmosphere, it lights up and burns up. And so each of those little shooting stars is just a grain of sand or a dust moat. Occasionally, we'll get a quarter-sized thing.

2:44Yeah, so just to be precise, if I go down to the beach and pick up some sand, that's the exact size I could be looking at, or smaller? A lot of times, it's much smaller than that, even. So why does something that small cause something that we can see? I mean, it must be crashing into the atmosphere, you know, hundreds of kilometers up. How come we can see it so brightly? Well, you're converting matter into energy, and any time you do that, you get a lot of light. It's possible to provide electricity for a city with a potato if you're able to convert the potato's

3:17mass into energy. Well, when we burn up that dust in the atmosphere, we're converting the mass into energy. It's heating up, it's burning away, and we're getting light as a result. And there's a lot of light trapped in a dust moat if you heat it up hot enough. So I guess, how much energy do these grains have? How are they getting, you know, so much energy in them? Well, these dust moats are, in some cases, hitting the atmosphere at 71 kilometers per second. And that speed is causing them to hit gas molecules and get them excited and that emits

3:53light, and they're burning up and they're emitting light. So it's, for a moment, we're getting as much light from a dust moat in the atmosphere as we're getting from a distant star. Right. Okay. So the comet is moving very quickly, and it's shedding off this material, and the Earth is moving at a certain speed in its orbit, and then you kind of are adding the two velocities together, like a car crash, the dust hitting our atmosphere, Earth is moving, and you get this bright flash. Exactly.

4:23So what happens if something a little larger hits? Well, a little bit larger initially just gets you a bigger flash. Occasionally, you'll see a small rock hit the atmosphere, and that small fist-sized rock looks like a small explosion in the sky. Suddenly, instead of having something as bright as a distant star, we have something as bright as airplane lights. As things get bigger and bigger, you get streaks that last longer, because it takes more time for the dust moat, or in this case, the rock, to burn up in the

4:55atmosphere. I think I've seen a couple of those. You just see like a streak that goes across the sky. It can go quite a distance, and it just kind of stays there in the sky like a line. It can last for seconds, tens of seconds, sometimes almost a minute. It's quite amazing. So what you're seeing is two different effects. You're seeing the rock basically getting destroyed as it burns up through the atmosphere, and you're seeing the heated up gas left behind from its passage. So the fact that the streak moves across the sky and appears to stay there for more than

5:32an instant, that's the hot gas taking time to cool back off. So lots of different things are going in. There's complicated physics involved in what's going on with our atmosphere to allow us to see such a fabulous fireworks show. So let's go bigger. So you get bigger than a rock. You start getting noises. You can actually hear the crackling as it goes through the atmosphere in some cases. You get bigger glows. You see them across larger parts of the sky. You start getting people reporting UFOs. Once you get to something a few meters in size,

6:09you get spectacular explosions. And once you get up to 50 meters in size, objects can actually make it all the way through the atmosphere. So they start burning up, get smaller, get smaller, get smaller, and something makes it all the way through and hits your house, hits Antarctica, hits the ocean. These things are raining down all around the world.

Amateur tracking and meteorite recoveries

6:30Now we talked about how amateurs can get involved in astronomy last week. And one of the things is if you happen to spot a meteor, spot a large object, spot a large trail, is there anything you can do as an amateur to help out astronomers? Well, a couple different things happen. First of all, there's random meteors on any given night. And they're not all associated with comet tails. Sometimes we actually just intercept a small asteroid in space. And if it's small enough, nothing bad happens.

7:05And usually those aren't detected until they decide to come down. And there's been a few found, I think there was one recently found around the Great Lakes region, where a bunch of people observed this bright object in the sky. They calculated, scientists took all of these observations and calculated a assumed trajectory and then went in search of the meteorite. When something hits the ground, it's a meteorite. When it's in the process of going through the atmosphere, it's a meteor. And before

7:35it gets to the atmosphere, it's a meteoroid or asteroid. So we had something similar to that happened in Canada. We had, there's one up in the Yukon. It was about four years ago, I think. And the same thing that, you know, lots and lots of people saw the trail and they knew, they calculated it was big enough that it probably made it through. And it ended up hitting a lake, a frozen lake in the middle of the, of the winter. And so, um, they were able to pull the fragments out and they were, it was, they were like perfectly preserved. So it wasn't like it hadn't gotten rusted. It had

8:06nothing. So yeah. Yeah. So if you see one of these and it seems noteworthy, write down what you see before you have a chance to forget anything, write down where you're looking from, where things appeared relative to objects that, you know, their locations and they're not moving objects. And then listen to the news. A lot of times when this stuff happens, uh, the news will say, if you saw something, call up certain scientists, uh, go to a certain website. And there's also amateur, um, observing clubs that

8:38track these things. This is particularly true with meteor showers. We work to figure out the exact orbits of comets by keeping track of when we intercept the most dense region of their tails. Um, so their tails go through space, leave behind a trail of material as the earth passes through the edge of where the tail used to be. We start getting an increase in the number of meteors that we see an increase in the number of shooting stars that we see. And we get more of an increase, more of an

9:11increase, more of an increase. And the moment that we have the largest number of shooting stars per minute is when we're going through the densest region of where the tail once was. And then the numbers go down, go down, go down as we exit the place where the tail used to be. And I guess this depends on how long ago the comet came through our neighborhood, right? From year to year, we get a different number of meteors per minute. We get a different level of storm based on how recently

9:43the, the comet that caused the meteor shower passed through this part of the solar system. Over time, we pick up more and more space junk and it's not there to be picked up on the next pass through. And over time, it dissipates through space. And so the years with the most significant meteor showers are the years right after the comet has gone through the inner part of the solar system. And so what are some of the comets that are causing some of the meteor showers?

Comets behind major showers

10:11Well, what's kind of cool is the most famous comet of all, comet Halley, is actually responsible for one of the minor showers. The Eta Quarids, which are visible primarily in the southern hemisphere are caused by comet Halley. The Earth actually passed through Halley's tail in 1910 while Halley was in the inner part of the solar system. This caused widespread panic, chaos, mass buying of gas masks. People were actually afraid that as we passed through the comet's tail,

10:43there would be poisonous gas put into our atmosphere. So people in their paranoid fear went out and bought lots of gas masks. Generally, this is a pretty minor meteor shower, but when you're actively going through the tail, it's fairly significant. Komen Enki, which is another fairly well-known comet, is also responsible for a meteor shower. And at one point, it was also quite possibly responsible for a great amount of destruction. So nowadays, we get these two meteor showers,

11:17the southern and northern torrets. The comet Enki comes from the solar system every 3.3 years. This is a pretty good meteor shower. It gets replenished fairly often. Now, comet Enki is believed to have once been a much, much bigger comet. And a couple thousand years ago, it is thought to have broken up. And when it broke up, some of the chunks that used to be part of the comet landed in the Middle East,

11:48possibly in the Fertile Crescent. And when they did this, it affected our atmosphere. It affected civilizations in general. It's thought by some that the prosperity of several Bronze Age civilizations was brought to a sudden halt by the impact of these comet fragments. It's also thought that the Tungusta event in 1908 may have been another fragment of this comet that now a part of it is

12:18comet Enki. So comets can seriously impact civilizations. Luckily, this doesn't happen very often, but it does still happen. And it could still happen again in the future. So what are the best, you know, apart from, you know, comet Enki raining debris across the hemisphere, what are the good meteor showers and storms we can look for? Well, the storms that can be counted on the most are the Perseids, which were caused by a comet

12:51Swift Tuttle and the Geminids, which are actually caused by a dead comet. There's this object 3200 Patheon that is thought to be a now defunct and not producing a big tail former comet that has been crusted over with cosmic dust. Every year, these two storms, which occur in August and November, they come, they shower, it's consistent. It's pretty much always a good storm that you can count on for

13:22a fun time out looking at the sky. Yeah, the Perseids, my favorite, mostly, I think, because it's warm. So, you know, we can, we can lay outside and the kids don't cry too much, you know, daddy, I'm cold. And we can, and we can watch the, and watch the meteor shower and they love it. But, you know, but I think my favorite one ever was just a few years ago was the Leonids. Yes. Which was just like nothing I've ever seen. No, there, there was a really fabulous storm a few years ago because the comet that causes it had

13:56actually recently passed through this part of the solar system, Temple Tuttle's on a 33 year orbit. And back in 99, it had just finished going through the system and we got this fabulous storm related with that. Yeah, I was, I was in Vancouver at the time and I went out, I sort of went out, wasn't even sure I was, it was going to be too bright or something. I went outside, it was very cold and, but it was clear, which was great, which normally in Vancouver in the winter, you don't, you get, get that, you just get rain. Um, but it was clear and it was just, it was astonishing. It was in the middle of the city, super bright lights and it was just, you know, streak after streak

14:30after streak, you know, every couple of seconds, just zip, zip, zip in the sky. And I was out there for probably three or four hours, just couldn't believe it. Yeah. Some of these storms can get really spectacular. You can get hundreds of things per hour, sometimes thousands per hour that you can see. And it's actually even led to songs. Back in 1833, there was a lenient meteor shower that was referred to as it was basically raining meteors. And then again, in 1933, there is a fabulous storm

15:07that was particularly spectacular in Alabama that led to the writing of a jazz standard called stars fell on Alabama. So from year to year, you can get various storms and sometimes it literally looks like it's raining stars. Now I know that for many things in astronomy, it kind of depends on

Viewing geometry and location

15:27where on the earth you live. Like if you're trying to see an eclipse and you live on, you know, the part of the earth that doesn't have the shadow falling across it, you just don't get a chance to see it. So some people are like, yeah, we saw an eclipse and other people don't get to see anything. Does, does where you live on the earth matter for, for what you're going to see with a meteor shower? Yeah, unfortunately it does. In general, you can see part of the meteor shower, no matter where you are on the planet, because it takes time for the earth to pass through the debris trail. But the most concentrated part of the debris trail might be quite small and only

16:01impacting our atmosphere for an hour or two. So when we talk about meteor showers, we were naming them after the constellations that the meteors appear to radiate from. So if you go out to see the Leonids next month, they peak around November 17th. You want to look up at the constellation Leo. And what you'll see is the meteor trails all appear to streak away from the constellation Leo. Now to see the best part of the storm, you want to be on the part of the planet that has Leo

16:37straight overhead so that it's high in the sky, far away from all the sludge that's along the horizon at the moment that the earth is passing through the densest part of the debris. Now the whole planet can't have Leo straight overhead at the same time. So where you are, it has to be dark. Unfortunately, you can sometimes go through the densest part of the debris trail while it's still daylight, and you want the constellation to be high in the sky. Now, we have done lots of calculations using year

17:11after year of observations to figure out exactly where the densest parts are and where you need to be on the planet. And there's websites out there that all you have to do is Google the name of the storm you're interested in, and they'll pop up maps of, okay, at this time in this location, it'll be really cool. At this time in this location, you're in daylight and you're stuck. And the other thing you also have to keep an eye out for is where is the moon? The moon produces a lot of light. If you go out during a full moon, it actually casts giant shadows and you can read very big letters in newspaper.

17:48Yeah, that's what we had with the Perseid meteor shower this year was the moon just totally washed it out. It was, you know, we saw some, but it wasn't anywhere near as good as the year before when there was no moon. Yeah, it was almost full. But this year's Leonids, it's around new moon. So the moon isn't going to impact our ability to see the Leonids. Unfortunately, for those of the United States, we're just in the wrong part of the planet. To really see the Leonids, well, you need to be in Europe. But we'll still see some shooting stars over here. So as with eclipses, sometimes it's your

18:21year for the, to see the meteor shower, and sometimes it just isn't. It's just where you live on the planet. Exactly. And sometimes the oceans are the only ones in luck, and then you need to get on a boat. So what can you do then to sort of improve your chances and sort of improve your meteor shower? Well, the first thing you want to do is go somewhere with dark skies, and you want to do this strategically. So say that from where you are, Leo is a constellation that you have to go north

18:53to see. So if you live on the south side of a big city, you may think, well, let's just drive south. The nearest dark skies are south of me. Well, then you're looking north over the big city to see Leo. So your most light pollution is going to be on the same horizon that's closest to the constellation you're interested in. So that's bad strategy. You want to figure out what direction is the constellation in and drive in that direction and find dark skies. So go somewhere dark where the

19:26horizon nearest the constellation is also dark. That'll really help. Most of all, you want to lie down and look up. The entire sky will get meteors. They'll all appear to be radiating from roughly the same point, but they may get a different distance away from the constellation Leo before they start to light up. So lie down, look up, unfocus your eyes, and just wait to catch motion, and then focus your eyes where you see the motion. Use wide angle cameras to try and catch them on film. And something

19:59else you can do is you can actually try and record where you see them coming from and make your own diagram to prove that they're all radiating away from Leo or whatever constellation is associated with the meteor shower that you're able to go out and see. So won't you see some right like just as the sun's going down? Yeah. So there's all sorts of neat geometry things going on. If say the Perseids are going to be straight overhead at midnight, well, that means that right about sunset, you have the

20:30Perseids occurring low on your horizon. And sometimes the dust particles, the grains of sand that are impacting the atmosphere actually skip across the atmosphere like skipping stones on a pond. And we can end up getting earth grazing meteors when we're at a right angle to where the actual storm is taking place. And these are pretty slow and bright. Yeah. They're slow, they're bright, they're really cool, a little bit explosive sometimes. So there's all sorts of different

21:04combinations. And on any given night, different parts of our atmosphere are hitting rocks, hitting dust, hitting sand. Very, very rarely does anything make it to the surface of the earth. But we're fairly constantly hitting small things that you can see at any time of any day of the year.

Calendar of annual meteor showers

21:22So let's talk about the big showers and storms of the year so people can kind of mark their calendars. So they're going on on a regular basis. The next big one we have coming up is the Leonids, which is November 17th. But even if, but hold on, even if, even though we're having this conversation in 2006, they happen every November 17th ish. They happen every mid November. Exactly which day they happen varies year to year because comets orbits are constantly getting slightly tweaked by

21:54Jupiter. So days may vary, but right around November 17th. But even if this is 2007 and you're in early November, the Leonids are coming. Yes. Then there's my personal favorite, the Geminids, because I was born during the Geminids. It occurs around December 12th to 14th every year. In January, we have the not quite so bright, I'm going to mispronounce this and I'm sorry. It's the Quadrantids. And that's early January to bring in the new year. Then in late April, around April 22nd or so, we have the Lyrids.

22:29In May, we have the Eta Aquarids, which are the ones that are caused by Halley's Comet. And then, as we were talking about, we have the Perseids in August and then the not quite so well known Ariads in late October. So around October 21st, we have those. So right now, plan a trip in the winter if you can handle the cold, or I guess if you're in the Southern Hemisphere, it's nice and warm. But also, plan a vacation for the time of the Perseid

23:01meter shower. Organize to get a bunch of your friends and family to get outside and watch them. And the moon is being good. Both the Leonids and the Geminids shouldn't be too affected by the moon this year. That's perfect. All right. Anything else? We covered all the meteor shower madness we can imagine? I think the coolest thing to do is just go out, look up, and take some friends and take something hot to drink. Be patient. Talk all night. Yeah. And use it as an excuse to get to know

23:32the sky. Challenge yourself to identify constellations while you're waiting for the next meteor to shoot across the field of you that you're looking at. And just have fun. Yeah. If you're the knowledgeable one, use it as an opportunity to point out the constellations to your friends. And take us along and feel free to play us so that you can annoy all of your friends with our voices while we talk to you and to them about what's going on in the skies above. And once again, I think you can have some homework for this episode as well, because with the Leonids coming up, let us know how it went for you. Did you get a chance

24:07to go out? Did you see them? How were they this year for you? We'd love to hear what you said. So our email address is info at astronomycast.com. All right, Pamela. Well, thanks again. That was great. And we'll see you next week. Sounds good. Thanks a lot, Fraser. This has been Astronomy Cast, a weekly fact-space journey through the cosmos. Music provided by Travis Serrell. Thanks for listening.

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