Date: January 6, 2011
Title: Shooting Stars Are Not Stars
Podcaster: Rob Berthiaume
Organization: York Observatory
Links: www.yorkobservatory.com
www.youdontfreezeinspace.com
Description: Seeing a ‘falling star’ or ‘shooting star’ is one of the most exciting and magical experiences we can have while out on a clear night under the stars. But these are more than just flashes of light that elicit a swarm of wishes. This podcast will go over what they are and why they’re important to astronomers.
Bio: Robert Berthiaume is working towards an MSc in atomic physics at York University in Toronto, Canada. When he can get away from building diode lasers, he rides his motorcycle when the sun is up, and shares the stars with the public at the observatory when it’s not.
Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by My Tea Shelf, an independent organic tea crafter specializing in herbal tea blends using organic herbs and real fruits. Indulge yourself with a delectable infusion. Visit myteashelf.com and get 10% off of your entire order including tea infusers and essential oils. Enter coupon code 365ASTRO.
Transcript:
Hi there. I’m Robert Berthiaume bringing you the January 6th edition of the 365 Days of Astronomy Podcast from the York University Observatory in Toronto, Canada. At some point when you have been outside after dark, looking up, you may have had the good fortune to see a bright streak of light, jetting across the sky faster than any plane or bird, only to fade and disappear again into the darkness. If you were quick enough, you may have made a wish upon this shooting star, or falling star, or maybe it was so bright and long-lived that instead of thinking about wishes, you were simply taken aback and left to gaze in wonder. In any case, immediately afterwards, you would have exclaimed “Did you see that?” to anyone else around, sharing the excitement with those who did, and leaving anyone who didn’t thouroughly disappointed.
These beautiful events happen all around the world, all the time, and given enough time looking upwards, anyone can see one. These shooting stars, however, have nothing to do with actual stars.
The points of light you see above you at night are stars, humongous balls of gas, trillions and trillions of kilometers away, glowing due to the nuclear fusion happening in their tremendously hot cores. A shooting star, on the other hand, is light coming from only a hundred kilometers up, when a small piece of dust or rock or metal falls into our own atmosphere, heating up the gases around it on entry.
Even though space is a pretty big and empty place, there is a lot of junk and debris floating around up there. As the Earth orbits the Sun, all these little pieces of stuff, called meteoroids, are orbiting the Sun as well. If a meteoroid gets close enough, Earth’s gravity will pull it towards the surface, and it falls through the atmosphere on the way down. But it does more than just fall.
Try this: put your hands together, and rub them together slowly. Now a bit faster. Now even faster. Now as fast as you can. The faster they go, the hotter they get. Your hands are probably moving a few meters per second at their fastest…Imagine they were moving tens of thousands of meters per second. Your hands would probably instantly vapourize while the rest of you , and the chair you’re sitting on, would light on fire. This is sort of what happens when with a meteor. A piece of rock or metal the size of a grain of sand, typically, falls through the upper atmosphere at tens of kilometers per second. The whole thing gets really hot and breaks into powder 70-100km up, leaving nothing to fall to the surface. While this happens, the the air around the object is pressurized so much in such a small amount of time that it heats up and glows, which is what we see as a shooting star.
After the shooting star fades, you may still see a ghostly trail greenish or bluish in colour left over, this isn’t your eyes playing tricks on you, but a trail of ionized gas, molecules with electrons knocked off while the meteoroid streaked by. These can act like giant antennaes, and if you have an FM radio tuned to a far away station, you can use it to listen for meteors even if it is cloudy and you can’t see them.
You can see 5-10 meteors from any place at any time with dark skies. These are called sporadic meteors, and they’re caused by stuff just out in space falling to Earth. But every so often, Earth’s orbit intersects the orbit of a comet. Comets spew gas and dust off their surface which then follows them in the same orbit. Think of a big ring of debris circling the Sun. Now if the Earth’s orbit happens to intersect this orbit, then every year, the same week, there are more meteors than usual. These are called meteor showers and we can see anywhere between 10 and 100 extra meteors per hour typically. Better yet, if there happens to be a big clump of really dense debris there when the Earth passes through, we can see thousands of meteors an hour during a meteor storm. These were historically scary things to see when people didn’t understand it. These days, with nothing to fear, I can’t wait for one to happen.
Most meteors are caused by objects very small in size, and they turn into dust before reaching the ground. But of course some are larger, and if they are large enough, a fragment makes it to the surface. By the time it reaches us here on the ground, the atmosphere has slowed it down to terminal velocity, so it isn’t falling any faster than a rock dropped from a skyscraper would be. All in all, though, several thousand kilograms of meteorites fall to the Earth every day. Picture a few dozen bathtubs filled with sand and rocks to get an idea of how much stuff that is.
I should probably clarify now what a meteorite is. I’ve talked about meteoroids, small things that are floating through space and entering our atmosphere. A meteor is the event you see, that streak of light. A meteorite is something that you or I can pick up off the ground, the remains of the meteoroid once it is on the surface of the Earth.
Meteorites are very important to scientists because they allow us to study material from other objects in the solar system or from the early solar system, without actually going to these other places, or even harder, back in time. Over the past 4 billion years, volcanoes and techtonic activity and wind and waves have changed the material the Earth was made of, so we don’t have a good idea of what things were like when it all started. But meteorites haven’t suffered the same effects of aging and erosion. Some meteorites were formed at the start of the solar system, and have been in space ever since, never touching or being touched by anything for 4.5 billion years. Collecting these samples shows us the building blocks out of which the Earth and other planets were made. Some of these meteorites are a result of a smashed up asteroid. When we look the chemicals in the meteorites here in a lab, they look just like the chemicals we see by doing spectroscopy, or looking at the special colours given off by asteroids in space. We can safely assume that these were all part of the same thing at one time, so it’s like having a sample of that particular asteroid. Even the Moon and Mars have provided us with meteorites, so we have samples here on Earth of the Moon and Mars without even going there.
If you’d like to hold on to your own little piece of space stuff, you can purchase samples online from various places. I would definitely avoid ebay and the like, to avoid purchasing a something for too much or purchasing something that may not even be a meteorite. But there are several reputable dealers, namely members of the meteoritical society, who are happy to help you acquire a sample or even start a collection. I actually recommend it. I have my own marble-sized ‘rock from space’ that always fascinates people and stimulates great astronomy discussion wherever I show it off.
Thanks for listening, I hope you learned something and had a little fun. Until next time, this is Robert Berthiaume wishing you all clear skies and good times.
End of podcast:
365 Days of Astronomy
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