We see the Perseid meteor shower peak every year around August 12, meaning the meteors we see are at a fixed position relative to the sun, right?
I read that the meteors are associated with the Swift-Tuttle comet, so presumably, that point is where the comet’s and the earth’s orbits coincide. But the comet is only at that location once per orbit, so do those little rocks and dust particles just hang out? Or is there a constant stream of rocks following the orbit of the comet?
Surely they must also be in orbit around the sun? They can’t just be floating there motionless in the orbital path.
They are – that’s what Fear Itself’s cite says. And that’s why the earth gets struck by meteor showers for the Perseids about the same date every year (and the Taurids, and the Orionids, etc.)
To clarify this, the particles which make up the showers are in orbit around the Sun and they roughly follow the originating comet’s orbit. Earth crosses this orbital path at approximately the same time each year; this is true regardless of the comet’s orbital period, which can be (and usually is) much longer than an Earth year.
You’re right - It does say that, although not as clearly as has now been explained.
I don’t know much about Swift-Tuttle comet, but I imagine that it has a highly elliptical orbit. Is the stream of particles pretty much evenly distributed along that orbit, or is the stream denser immediately behind where the comet has just been?
Both. Once a comet has completed lots of passes through the inner solar system, the gunk it spews out will have dispersed fairly evenly and filled up the entire cometary orbit. That’s why you can get a shower like the Perseids every year, regardless of where the comet is.
But yes, when the comet again passes through the inner solar system, the gunk gets “refreshed” and is thicker in the vicinity of the comet. That’s why some showers like the Leonids periodically turn into “storms”, when the originating comet is relatively nearby.