On average, how long is the tail of a meteorite (falling star)?
I am having trouble finding the answer to this. It seems to vary a lot, depending upon the composition of the meteor, its speed, and the angle with which it strikes the Earth's atmosphere. I am noticing a lot of webpages which indicate that (roughly) 10 to 20 miles is a reasonable length for a meteor trail, but I don't know if you need to be more precise?
The following NASA page states that meteors leave a trail stretching from 40 to 75 miles in altitude at the top, down to 30 to 60 miles in altitude down at the bottom. But, of course, that only includes the vertical vector. A meteor travelling in a more horizontal direction could have a longer trail. http://www.nasa.gov/worldbook/meteor_worldbook.html
I hope this is sufficient for your purposes. If you need a more exact answer, please get back to me and I will try again.
Keep Looking Up, --Ed