reply to post by scubagravy
You're welcome scubagravy.
I think you have indeed grasped the concept. Well done.
It's easy to forget that Earth and its atmosphere are both curved, which also plays a part in misleading the unwary. The same concept also applies to
aircraft, in that they may be flying at constant altitude, but if you observe an aircraft flying away from you on the ground, it simply gets lower and
lower in the sky, apparently.
If the sun happens to be setting, and the light illuminates the contrail under the right atmospheric conditions (making short-lived contrails), this
has
fooled allot or people in the past.
Here's another clip although not the extremely short contrail and foreshortened
due to perspective, but it's nice clear footage.
Now consider an aircraft traveling in the opposite direction to the examples above, so that it's coming towards you, instead of flying away from you.
It would appear to move up and away from the horizon, right?
What would happen if the engines then cut out at just the right time and the aircraft continued along its path without turning left or right? It could
crash into you, if the timing was right, but this is a highly exaggerated example - in real life you might be able to observe the aircraft for a good
few minutes as it approached you, and it would have to cut out much nearer to overhead than a meteor would, if it was to hit you. I think anyway. I'm
no aircraft expert, and I could be wrong about that. It would depend on the initial altitude and gliding capabilities I guess.
Once a meteoroid is decelerated enough by the atmosphere (towards the end of the luminous phase/start of the dark-flight phase), it's trajectory
would become progressively more curved (like an artillery projectile).
In extreme cases where a significant portion of the cosmic velocity (around 1km/s+) is retained all the way into the lower (thicker) atmosphere by a
very large object, the object may have ceased to be luminous (not sure where the cut-off velocity for that is, but I suspect it's around 2-3 km/s)
but could still impact the ground with enough energy to cause some localized damage.
If you were unlucky enough to observe a meteor like this before being hit, it would not appear to move much (close to being a "point-meteor", but
not quite), but just get brighter and brighter, till it faded out, and then hit you a few seconds later.
Had the angle been different, the Great Lakes daylight fireball of 1972 might have hit the ground in a manner similar to the above example, but as it
was, it just skimmed the atmosphere and went back out to space.
This is footage that most probably have not seen before. I hadn't, but came across it just now whilst looking for the well known clip (2nd clip
below).
Just for comparison, here's footage of the Peeskill Fireball, which dropped a meteorite in upstate NY, hitting a car!
The above two events are the longest events ever to be captured on camera as far as I know. I think the Peeskill fireball was observed for 60 or 70+
seconds.
Anyway, the info above should give you a better idea of how to work out which way a meteorite might fall. The most reliable way to work out a fall
site is to use photographs or video if they are available and triangulate the trajectory, but failing that it can usually be done by gathering witness
reports, although more are usually discarded than are used. The most reliable/valuable reports tend to come from amateur/professional astronomers
since they can plot the path accurately using the stars and other celestial bodies for reference.
One (more) thing to keep in mind, even with my experience, I find it hard to work out which way a meteor is traveling (away or towards me), unless it
can be identified as a member of a meteor shower. Meteors belonging to showers are generally not as bright as the types of object we have been talking
about, which might be better described as small-medium sized asteroids.
Going back to the suspected meteor in question, if it was an earth grazer that was observed, it may not even have reached 40 km altitude before
heading back out to space or "burning" itself out.
I'm not sure thinking about 40 km as a "cut off" if you are, is a good idea. It's just that in the vast majority of cases, meteors have been
slowed down to the point that they can no longer impart enough energy on the air to make it glow as the meteoroid passes through it by that
altitude.
For any given meteoroid/object, that cut-off could be at almost any altitude. There are always rare exceptions to "rules" like this, but for the
reasons I gave above, I think it's unlikely that the meteor reached 40 km altitude whilst still luminous in this case.
I'd have to check to be sure, but it's either 20km or 40km where the air becomes thick enough for a sonic boom to propagate down to the ground, so
if no booms were heard directly below the meteoroids flight path (assuming it's a populated area), that means nothing made it below that altitude,
and that's pretty much case closed for me.
Booms are usually quite a good indicator of meteorite falls. Check previous threads here on ATS, there are fairly numerous examples. Here are just a
few threads that I took part in recently (heated at times!):
UFO - meteor like object with sonic boom above Dallas and Austin Texas!
Massive object crashes over Edmonton, Canada
Loud explosions in Hampton Roads area
[edit on 21-6-2009 by C.H.U.D.]
that's *exactly* what one looks like. 
There will be more to come. 
