Why Annual Meteor Showers Happen Every Year

Space is big, really really big. And there's a lot of stuff in it. "Never" is a big word, but it's going to take a very long time to clear out that region with our tiny little ball of dust.

I mean it will eventually. But the comet that the meteors break off from is big and it only passes around the sun every 133 years. So it'll take a lot of generations of humans before the sun consumes it.

Fun fact: a Finnish astronomer has predicted the perseids peak in 2028 (the night of August 12) could potentially be a "meteor storm". Meaning there could be over 1000 meteors per hour. Last year's peak was only about 100 per hour.

The Perseid debris field is about 65-100 million kilometers wide; the earth is 12,742 km wide

shouldn't the Earth clear out any lingering meteors after a few revolutions?

This question grossly underestimates the size of Earth's orbit. It's not like a table with some crumbs you can brush off with your arm, it's like a gymnasium that you're sweeping with a toothpick.

Meteor showers are usually formed from dust kicked off by comets. The dust spreads out following the orbit of the comet like this:

Every year as the Earth goes around the Sun, there's a few days where it passes near the orbit of the comet and its dust, and so every year on those days the dust hits us to form a meteor shower.

(And in case you're worried, the comet itself won't hit us: its orbit doesn't quite line up with the Earth.)

A few things. First, most orbits aren't completely planar. Just look at our moon in that we sometimes get an eclipse during a new/full moon and sometimes we don't. Second, the particles ejected from the comet aren't statically floating there. Many have some momentum from when they were ejected but not enough to escape the sun's orbit. As a result, by the time Earth revolves around the sun, it's going through a slightly different area of the debris field and a lot of the debris that wasn't originally in the path of Earth has moved into it.

Give it enough time, the debris will eventually be cleared out. But time on an astronomical scale is a long, long time for humans.

I understand that meteor showers are due to the Earth passing through the debris left by a comet, but shouldn't the Earth clear out any lingering meteors after a few revolutions?

There are streams of meteroids that intersect the Earth's orbit. Each time the Earth passes through the stream, a bunch of the meteroids in the stream hit the Earth's atmosphere and turn into meteors. These streams are made up of the debris left behind by disintegrating comets.

There's a nice figure here if that helps visualise things.

Most "meteor showers" are occasions where Earth's orbit intersects the orbit of a comet. when comets are in the outer solar system, they are mostly stable, but when they are close to the sun, they lose a lot of mass due to solar radiation. Those are the tails of the comet that we often see. That dust doesn't just go away though. When the Earth passes through the orbit of the comet, it'll run through the area where that dust is, and it burns up in our atmosphere as meteors.

The particles that form the meteor shower are not just sitting there in space. Rather, they follow approximately the same orbit as the comet they came from, albeit with a spread of some millions of miles. Earth, by comparison, is tiny and only sweeps out a tiny portion of this cloud of meteoroids.

I stumbled upon a recent meteor shower and it got me wondering how we could know when something like that is going to happen in advanced? I was also wondering if we know the average size of the meteors that we're seeing is?

How are they exactly in sync with the earth's year instead of appearing every 17.3 months or something arbitrary?

The Perseids come from a stream of stuff that contains hundreds of millions of tons of mass. (We don't know exactly how much.) Each time we pass through, we hit about 100-200 kg worth of them. So you'd think we'd thin them out over millions of years. But, every 133 years or so, the comet called Comet 109P/Swift-Tuttle goes by and drags a bunch more stuff into the cloud.

On planetary time scales, it will eventually thin out, but on human time scales, it's probably going to remain pretty much the same as it is now.

They alaways seem to peak at 12-4am or so as opposed to 9-midnight. Im on the east coast of the US.

edit: thanks for the explanations. Makes total sense now, I wish I had asked earlier!

Meteor showers occur as the Earth moves through the path of debris in space. Wherever your location on Earth is, after your local noon, you are "behind" the direction of Earth's travel until midnight. After midnight, you are now on the "front" side of Earth's travel. So, after midnight, you're facing toward rather than away from the debris in space. The shower picks up after midnight and lasts until morning approaches and the sun's light drowns out the meteors just as it does the stars.

The Geminids meteor shower happening this week got me wondering. This question may have a very obvious answer but I just doesn't seem very simple to me.

This is a consequence of orbital dynamics.

Let's say there's a spacecraft in an orbit and it fires its thrusters in some direction, to put itself in a slightly different orbit. If it only changes the orbit a little bit in one direction, how much can it change its orbit? As it turns out, with only a small amount of motion it can't really move out of its orbital track much. But it can drift a little one way or the other. And by changing its orbital period a little it can, over time, end up at a very different position along the orbital track than it would have been at originally.

A comet going around the Sun will shed a bunch of tiny pieces of itself as it disintegrates while its ices heat up and vaporize as it gets closer to the Sun. Dust grains, pebbles, even some chunks of rock. Those little pieces will end up in slightly different orbits around the Sun compared to the original comet, but they'll all stay in roughly the same orbital track. If the comet's orbital track intersects the Earth's orbit then Earth will plow through that orbital track and also the cloud of debris at the same time every year.

Pretty self explanatory, but if the earth is just “floating” in space with no ups or downs why would meteors hit some places of the atmosphere with a higher rate than other places? Or is it that in some places it’s harder to see?

I hope to be asking in the right subreddit.

there you see them falling stars some call it they appear out no where then disappear to somewhere . you dont hear them no boom no vibration silent . you know what they say it is you seeing but it dont add up to what you seeing. and how they they know the exact time going be and tell you so you wont miss it. that dont sound random to me out there so call endless space at lease that what we see and they tell us its way more out there and how thing operate like they been there. but you know they havnt they tell you they been to havard and use lots of science talk to quite you. you hypnotise and let them win. but you know what you see and all that 30 mins of so call explanation they give you dont explain again how they know when meteors showers come. is it really showers. what are we seeing here. in the universe.