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MeteorObs - an Internet forum for meteor observers of all levels
DID I ACTUALLY SEE A FIREBALL LAND NEAR ME?
People frequently report that they have not only seen a
bright meteor (a "fireball") in the sky, but that they've
actually seen it LAND near them on the ground! But however
convincing such a sight may seem to be, it is actually
vanishingly unlikely! To understand why, we will
have to talk right up front about what we know to be true
regarding meteors and meteorites...
For example, we know that the shooting stars we normally see
are actually VERY high up in our atmosphere - they generally
become visible at altitudes of 80 kilometers or more. And of
course, if you aren't DIRECTLY under the meteor, you will
see it at an angle, from much further off along our globe...
Second, we know that even bright meteors are usually from
very small particles: one the size of a house might light up
the sky like a second sun! And because of the tremendous
energy that a desk- or basketball-sized meteoroid generates
when it "belly-flops" into our atmosphere at over 30,000
mph, we know meteors almost NEVER survive atmospheric entry!
We also know that these small particles - especially the
ones which come from the meteor showers - are usually NOT
very dense. Instead of thinking of them as little rocks or
sand grains, the best analogy for them seems to be "Cosmic
Dustbunnies", or even "Celestial Cotton Candy". :)
Because of the the small size and low density of meteor-
shower meteors - even the very brightest ones - it's no
small wonder that a meteorite has NEVER been definitely
associated with a meteor shower! Instead, the kind of large,
hard, dense matter that could survive earth's atmosphere is
generally theorized to come from some where else - most
likely, the rocky "asteroids" between the planets. And these
objects are no more common during meteor showers than they
would be at any other time of year.
--
Finally, re: seeing a fireball apparently land nearby, there
are a few tricky things to keep in mind. These "tricks" trip
up essentially every non-meteor observer who is lucky enough
to see one of these bright meteors: folks like mathematicians,
engineers, and even professional (non-meteor) astronomers!
First, it is basically impossible for someone to "see" how
far away an object is based only on perspective, UNLESS they
also know the TRUE SIZE of that object! The reason we're so
used to believing we can judge distances is that everything
we see on the ground has a known size. But objects in the
sky, and especially unfamiliar ones, can play real tricks on
us here! (For example, basically all of us "see" the moon
and sun as being larger when near the horizon than when
they're high in the sky. But in fact, they're not at all!)
Second and even more importantly, meteorites do not "burn"
all the way down to the ground! Instead, they "flame out" at
a high altitude - usually at least 30km - and then go into
what's called dark flight. Essentially, after falling below
30km, they become mere "falling rocks"! By the time they
finally reach the ground at "normal" falling velocities,
several minutes after "flaming out" and becoming invisible,
they're generally not even very warm!
NOTE: The purpose of this page is not to discourage
you from reporting what you believe you saw! But it is
important when you see an amazing event like a bright
meteor, to have some context for understanding it. And
again, if you're confused, you aren't alone! Practically
every fireball report sent in by non-meteor-watchers - no
matter their background - describes the object witnessed as
having landed "a few yards away", "in the next field", "next
town over", maybe "a county or two over", etc. This is true
even when the same object has been witnessed by many other
people hundreds of miles further downflight!
Last of all, let me say that meteor science is NOT
completely known... It is just possible that you may have
seen something unique in our understanding (so far) of
meteors - a flaming meteoritic particle, which actually
remained "on fire" somehow all the way down to the ground!
No one can say this is "impossible", but do keep in mind
that the realistic chances of there actually being anything
there on the ground are vanishingly small...
Anyway, for those privileged to see a truly bright meteor,
it's to be hoped that the above information, coupled with
the thrill of the actual event, is enough to pique your
interest in learning more about meteors. If so, this site
and many others on the Web are a great starting point!
Clear skies!
Lew Gramer
<dedalus@alum.mit.edu>
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