November 18, 2024 • 11 mins
Every fall, the Leonid meteor shower puts on an amazing display with observers counting numbers from thousands to tens of thousands of meteors per hour. Joe Pesce, an astrophysicist with the U.S. National Science Foundation, discusses meteor showers, why they occur and how to view the Leonid meteor shower.
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Episode Transcript
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(00:03):
This is the Discovery Files podcastfrom the U.S.
National Science Foundation.
Every fall,
the Leonidmeteor shower puts on an amazing display.
Observers have noted varying numbersfrom thousands
to tens of thousands of meteorsper hour in years past.
We are joined by JoePesce, astrophysicist, educator
(00:23):
and a program director in the Divisionof Astronomical Sciences at the U.S.
National Science Foundation.
Doctor Pesce, as ever,thank you very much for joining me today.
I want to start by asking youwhat is a meteor shower?
So let me let me startby describing what a meteor is.
And then we'll get into the meteor shower.
So a meteor is a small particle of debrisfrom interplanetary space,
(00:45):
a dust grainor a small sand grains sand particle.
And it impactsthe Earth's atmosphere randomly.
And when it does that, it'scoming at very high speed and it burns up.
And we see that burning
objectas it travels through the atmosphere.
And so that's a meteor.
A meteor shower is a collection of these.
(01:09):
Right.
So meteors, debris and dust are randomlyhitting Earth's atmosphere all the time.
Some tens of thousands of tons
per year of dust impactthe upper atmosphere of the Earth.
And so they're coming in randomly.
But a meteor shower is an eventthat is caused
when Earth passesthrough the orbit of an asteroid or comet.
(01:30):
And asteroids or comets are dirty things,
and they're releasing a lot of debris,this dust and sand grains.
And as the Earth's orbit passesthrough the orbit of that object,
we encounter a higher number of meteors.
And so we call that a meteor shower.
It's not just a random event,
but there's a larger number perhour of these meteors.
(01:51):
You mentioned the dustbeing what we're seeing.
Does the makeup of the object these arecoming off of affect what we see?
Yes, to some extent.
So most of the particlesthat are coming off an asteroid
or comet are very small dust like,and they literally are.
That's not an analogy.
They are like the dustthat we have around us here on Earth.
They're very, very small.
(02:12):
You might ask, why are they so brightwhen we see them right
streaking through the sky?
And it'sbecause they're moving at very high
velocities and they get heated upand they turn into a plasma and shine.
So the large fraction of materialis in this very small state.
Comets are
certainly more activethan asteroids by definition.
(02:33):
As they come near the sun,they get heated up and material is blowing
off of their surfaceand that can be water, ice crystals.
Dust, sand grains and that sort of thing.
Asteroids.
There may be water particles,ice particles, but that's mostly rocky
material.
Depending on the on the body,you might get larger particles,
(02:56):
sand to a half inch,
centimeter sized pebblesand that sort of thing.
So yeah,the composition does affect things.
And and that material coming off is,has different elemental composition.
And that might affect the colorof the meteor, but generally not so much.
It's it's more of a size issue.
And so if it's a big particlethat's going to lead to spectacular,
(03:19):
you know, meteor streams that are bright
and longer duration than a typical meteorthat lasts a couple of seconds.
What is the Leonid meteor shower?
The Leonid meteor shower is a particularmeteor shower that occurs
late in the year.
And again,it's the Earth passing through the orbit
of of an objectthat's, spewing dust and gas.
(03:41):
In this case, it's a comet.
And the shower, the the meteors
appear to come from one area on the sky.
And in the case of the Leonidmeteor shower that happens
near coincide with the constellation
Leo, hence the name Leonids.
It peaks in about the middle of November.
(04:03):
That varies a little bit from yearto year.
The meteors that come fromthis meteor stream, occur
about a month, a couple of weeks
before the middle of Novemberand a couple of weeks after.
So we're looking at an eventthat happens annually
between the beginning of Novemberand the beginning of December.
Do we know where the meteor showeroriginated?
The Leonid meteor shower is debristhat is coming off of a comet
(04:28):
that has a 33 year orbitas it orbits in our solar system,
and it passes near the Earthand around the sun.
That occurs every 33 years.
And as it's traveling through the solarsystem, its debris is coming
off of the surface, mostly small dust
particles and small sand particlesyou can imagine
(04:48):
and so as that comet passes through thethe solar system,
it leaves this trailand that trail of debris remains in orbit.
And as the Earth passesthrough that location in the solar System,
we encounter a larger number
of dust particles,creating the the meteor shower.
(05:09):
And in this case, it's knownas the Leonid meteor shower.
Where will they be visible?
So theoretically,you can see the meteors anywhere
but meteor are typically relatively faint.
And so you really want to look for a darksite.
There's lots of light pollutionin the inner cities and suburban areas.
(05:31):
And so if you can avoid those areasthat are light polluted,
you know, go to a rural areanearby your house
where it's a little bit darker,and you're going to have
a higher probabilityof being able to see these objects.
Some of the meteors will be bright enough
that you could see anywhere,but most of them are relatively faint.
This year,
unfortunately,
(05:51):
we are going to have
a relatively bright moon,
and that's not
going to help the situation,but there's nothing we can do about that.
Do we need any special equipmentto see them?
No. This is the great thingabout astronomy in general.
And meteor showersand meteor showers in particular.
You just need your eyes.
And so you can typically see themwith the naked eye.
Usually they're happening randomlyon the sky and last only a few seconds.
(06:13):
And so that is the best way to see themwith the eye in a meteor shower.
You may be able to,because the large number of meteors,
you may be able to predictthat they're going to be a large number
in this particular area.
So you could use binoculars,
but the naked eye is the best instrumentand so it's accessible to everyone.
You mentioned being able to predictto some degree where they occur.
(06:36):
So how do astronomerspredict meteor showers?
If we've had a recordof a particularly high
number of meteors coming from one
particular area on the sky,and we see that over a couple of years,
we can be relatively certain that we'regoing through a a debris stream.
And so we can say, well, that happenedon, you know, the 1st of February.
And so next year it's going to be aroundthe 1st of February.
(06:58):
That can be donewhether you know the parent body or not,
that's causing the debristhat leads to the the meteors.
If instead, we truly doknow what the parent body is
and we can determine what its orbit is,
we know that that objectis in a ten year orbit.
And so it's coming around every ten years.
(07:19):
And, you know, we know whatthe orbital dynamics are because
we understand gravity in that solar systemwell enough that we can make predictions
for when that object is nearbyand feeding the debris stream,
and also when and if the Earth will passthrough that debris stream.
And so we can make those predictionsbased on a knowledge of gravity.
(07:39):
Fundamentally, do.
We have a long historical recordof meteors? Yes.
Records are spotty.
Some big meteor showers where you have
hundreds of meteors per hour or more.
You know, we can go back in the recordand find those.
And based on the time and location, we candetermine what meteor shower that is.
(08:02):
In particular, as long as the parent bodyhas been moving through the solar system
and leaving debris
in a way that the Earth encounters, thatobviously that's the important thing is
that the Earth is impacting thethe debris from from that object.
There will have been, a meteor shower.
There are always new objectsappearing, comets and asteroids.
(08:26):
And so in the future, are we going to havedifferent sorts of meteor showers?
Certainly in the past,were there different ones?
Yes, absolutely.
But these are usually long term events.
The number of meteorsthat occur in any given year
somewhat depends on the amount of materialthat's come off of the parent body,
(08:47):
and how long that parent body has beenin our location of the solar system.
So if it's a comet that travels throughthe solar system once every 1000 years,
it leaves debris as well.
But over time, that debris dissipates.
And so over time
until it shows up again, you know,and then in the next thousand years,
you're going to have fewer and fewermeteors that come from that shower.
(09:11):
But the answer is yes.
Almost certainly.
These have been long term events.
Okay. My last question for today.
Are there any surpriseswith these annual meteor showers?
There can be.
And it depends on how dirty the object is.
The body that's leaving the debris.
(09:31):
If it's a comet, how active it has beenas it's, you know, spewing material off
of the surface and how recentlyit's been in our neighborhood.
So, you know, we could have an, a comet
that is on a long period,ten, 20, 50 years.
And if we are at the end of that period,
(09:52):
the stream of debris might be lowin numbers, low density of particles.
And so, you know,when we expect a certain number, say,
ten meteors per hour, maybe
kind of towards the end of that periodwe might be getting 1 or 2.
And so that's a surprise.
If on the flip side, the parent objecthas been nearby relatively recently,
(10:13):
there may be a large number of particlesthat cause the meteors.
And so we see, a burst of activitywhen we normally expect ten per hour,
maybe there's 100 or 1000 per hour,maybe the particles are bigger
when the object has passedby relatively recently.
So we get large numbers of bright meteors.
And so this tends to happen.
(10:33):
But because the orbits for these objectsare usually long period,
the quality and the quantity of meteorsis pretty stable from year to year.
Special thanks to Joe Pesce.
For The Discovery Files, I'm Nate Pottker.
You can watch video versions
of these conversations on our YouTubechannel by searching @NSFscience.
Please subscribe wherever you get podcastsand if you like our program,
(10:55):
share it with a friendand consider leaving a review.
Discover how the U.S.
National Science Foundationis advancing research at NSF.gov.
This is the Discovery Files podcastfrom the U.S.
National Science Foundation.
Every fall,
the Leonidmeteor shower puts on an amazing display.
Observers have noted varying numbersfrom thousands
to tens of thousands of meteorsper hour in years past.
We are joined by JoePesce, astrophysicist, educator
(00:23):
and a program director in the Divisionof Astronomical Sciences at the U.S.
National Science Foundation.
Doctor Pesce, as ever,thank you very much for joining me today.
I want to start by asking youwhat is a meteor shower?
So let me let me startby describing what a meteor is.
And then we'll get into the meteor shower.
So a meteor is a small particle of debrisfrom interplanetary space,
(00:45):
a dust grainor a small sand grains sand particle.
And it impactsthe Earth's atmosphere randomly.
And when it does that, it'scoming at very high speed and it burns up.
And we see that burning
objectas it travels through the atmosphere.
And so that's a meteor.
A meteor shower is a collection of these.
(01:09):
Right.
So meteors, debris and dust are randomlyhitting Earth's atmosphere all the time.
Some tens of thousands of tons
per year of dust impactthe upper atmosphere of the Earth.
And so they're coming in randomly.
But a meteor shower is an eventthat is caused
when Earth passesthrough the orbit of an asteroid or comet.
(01:30):
And asteroids or comets are dirty things,
and they're releasing a lot of debris,this dust and sand grains.
And as the Earth's orbit passesthrough the orbit of that object,
we encounter a higher number of meteors.
And so we call that a meteor shower.
It's not just a random event,
but there's a larger number perhour of these meteors.
(01:51):
You mentioned the dustbeing what we're seeing.
Does the makeup of the object these arecoming off of affect what we see?
Yes, to some extent.
So most of the particlesthat are coming off an asteroid
or comet are very small dust like,and they literally are.
That's not an analogy.
They are like the dustthat we have around us here on Earth.
They're very, very small.
(02:12):
You might ask, why are they so brightwhen we see them right
streaking through the sky?
And it'sbecause they're moving at very high
velocities and they get heated upand they turn into a plasma and shine.
So the large fraction of materialis in this very small state.
Comets are
certainly more activethan asteroids by definition.
(02:33):
As they come near the sun,they get heated up and material is blowing
off of their surfaceand that can be water, ice crystals.
Dust, sand grains and that sort of thing.
Asteroids.
There may be water particles,ice particles, but that's mostly rocky
material.
Depending on the on the body,you might get larger particles,
(02:56):
sand to a half inch,
centimeter sized pebblesand that sort of thing.
So yeah,the composition does affect things.
And and that material coming off is,has different elemental composition.
And that might affect the colorof the meteor, but generally not so much.
It's it's more of a size issue.
And so if it's a big particlethat's going to lead to spectacular,
(03:19):
you know, meteor streams that are bright
and longer duration than a typical meteorthat lasts a couple of seconds.
What is the Leonid meteor shower?
The Leonid meteor shower is a particularmeteor shower that occurs
late in the year.
And again,it's the Earth passing through the orbit
of of an objectthat's, spewing dust and gas.
(03:41):
In this case, it's a comet.
And the shower, the the meteors
appear to come from one area on the sky.
And in the case of the Leonidmeteor shower that happens
near coincide with the constellation
Leo, hence the name Leonids.
It peaks in about the middle of November.
(04:03):
That varies a little bit from yearto year.
The meteors that come fromthis meteor stream, occur
about a month, a couple of weeks
before the middle of Novemberand a couple of weeks after.
So we're looking at an eventthat happens annually
between the beginning of Novemberand the beginning of December.
Do we know where the meteor showeroriginated?
The Leonid meteor shower is debristhat is coming off of a comet
(04:28):
that has a 33 year orbitas it orbits in our solar system,
and it passes near the Earthand around the sun.
That occurs every 33 years.
And as it's traveling through the solarsystem, its debris is coming
off of the surface, mostly small dust
particles and small sand particlesyou can imagine
(04:48):
and so as that comet passes through thethe solar system,
it leaves this trailand that trail of debris remains in orbit.
And as the Earth passesthrough that location in the solar System,
we encounter a larger number
of dust particles,creating the the meteor shower.
(05:09):
And in this case, it's knownas the Leonid meteor shower.
Where will they be visible?
So theoretically,you can see the meteors anywhere
but meteor are typically relatively faint.
And so you really want to look for a darksite.
There's lots of light pollutionin the inner cities and suburban areas.
(05:31):
And so if you can avoid those areasthat are light polluted,
you know, go to a rural areanearby your house
where it's a little bit darker,and you're going to have
a higher probabilityof being able to see these objects.
Some of the meteors will be bright enough
that you could see anywhere,but most of them are relatively faint.
This year,
unfortunately,
(05:51):
we are going to have
a relatively bright moon,
and that's not
going to help the situation,but there's nothing we can do about that.
Do we need any special equipmentto see them?
No. This is the great thingabout astronomy in general.
And meteor showersand meteor showers in particular.
You just need your eyes.
And so you can typically see themwith the naked eye.
Usually they're happening randomlyon the sky and last only a few seconds.
(06:13):
And so that is the best way to see themwith the eye in a meteor shower.
You may be able to,because the large number of meteors,
you may be able to predictthat they're going to be a large number
in this particular area.
So you could use binoculars,
but the naked eye is the best instrumentand so it's accessible to everyone.
You mentioned being able to predictto some degree where they occur.
(06:36):
So how do astronomerspredict meteor showers?
If we've had a recordof a particularly high
number of meteors coming from one
particular area on the sky,and we see that over a couple of years,
we can be relatively certain that we'regoing through a a debris stream.
And so we can say, well, that happenedon, you know, the 1st of February.
And so next year it's going to be aroundthe 1st of February.
(06:58):
That can be donewhether you know the parent body or not,
that's causing the debristhat leads to the the meteors.
If instead, we truly doknow what the parent body is
and we can determine what its orbit is,
we know that that objectis in a ten year orbit.
And so it's coming around every ten years.
(07:19):
And, you know, we know whatthe orbital dynamics are because
we understand gravity in that solar systemwell enough that we can make predictions
for when that object is nearbyand feeding the debris stream,
and also when and if the Earth will passthrough that debris stream.
And so we can make those predictionsbased on a knowledge of gravity.
(07:39):
Fundamentally, do.
We have a long historical recordof meteors? Yes.
Records are spotty.
Some big meteor showers where you have
hundreds of meteors per hour or more.
You know, we can go back in the recordand find those.
And based on the time and location, we candetermine what meteor shower that is.
(08:02):
In particular, as long as the parent bodyhas been moving through the solar system
and leaving debris
in a way that the Earth encounters, thatobviously that's the important thing is
that the Earth is impacting thethe debris from from that object.
There will have been, a meteor shower.
There are always new objectsappearing, comets and asteroids.
(08:26):
And so in the future, are we going to havedifferent sorts of meteor showers?
Certainly in the past,were there different ones?
Yes, absolutely.
But these are usually long term events.
The number of meteorsthat occur in any given year
somewhat depends on the amount of materialthat's come off of the parent body,
(08:47):
and how long that parent body has beenin our location of the solar system.
So if it's a comet that travels throughthe solar system once every 1000 years,
it leaves debris as well.
But over time, that debris dissipates.
And so over time
until it shows up again, you know,and then in the next thousand years,
you're going to have fewer and fewermeteors that come from that shower.
(09:11):
But the answer is yes.
Almost certainly.
These have been long term events.
Okay. My last question for today.
Are there any surpriseswith these annual meteor showers?
There can be.
And it depends on how dirty the object is.
The body that's leaving the debris.
(09:31):
If it's a comet, how active it has beenas it's, you know, spewing material off
of the surface and how recentlyit's been in our neighborhood.
So, you know, we could have an, a comet
that is on a long period,ten, 20, 50 years.
And if we are at the end of that period,
(09:52):
the stream of debris might be lowin numbers, low density of particles.
And so, you know,when we expect a certain number, say,
ten meteors per hour, maybe
kind of towards the end of that periodwe might be getting 1 or 2.
And so that's a surprise.
If on the flip side, the parent objecthas been nearby relatively recently,
(10:13):
there may be a large number of particlesthat cause the meteors.
And so we see, a burst of activitywhen we normally expect ten per hour,
maybe there's 100 or 1000 per hour,maybe the particles are bigger
when the object has passedby relatively recently.
So we get large numbers of bright meteors.
And so this tends to happen.
(10:33):
But because the orbits for these objectsare usually long period,
the quality and the quantity of meteorsis pretty stable from year to year.
Special thanks to Joe Pesce.
For The Discovery Files, I'm Nate Pottker.
You can watch video versions
of these conversations on our YouTubechannel by searching @NSFscience.
Please subscribe wherever you get podcastsand if you like our program,
(10:55):
share it with a friendand consider leaving a review.
Discover how the U.S.
National Science Foundationis advancing research at NSF.gov.
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