Expert: Tom Whiting - 9/29/2008

Question
QUESTION: Hello. I was in my backyard, looking at the night sky as i always do, and i saw what looked like a shooting star, but it was traveling upward at about a 45 degree angle. then after the streak of light came a very noticable flash of white light. Which i thought was very strange. And it wasnt a fireball like when a meteor penetrates the atmosphere.  Would you happen to know what it was that i saw?

ANSWER: Hi Daniel,
Well, I wasn't there, but my best guess is what you guessed, a meteor
with a terminal burst. A terminal burst is not unusual for a meteor.
After a very bright terminal burst, you want to listen for an explosive sound about 1-2 minutes later if you're in a quiet country-side setting. (If it's say 20 miles high, the sound will arrive in 100 seconds). Sometimes it sounds like very distant thunder, or a very distant dynamite explosion....for a few seconds.
Higher than 20 miles, then you usually can't hear it. (Not enough
air above 105,000 feet.)

The direction (up or down) is meaningless because there is no up or down in space; all that's telling us is that the meteor was heading toward your zenith, but we know by definition that this was an incoming particle or body).
Or if it's really bright and very slow, it could be a satellite orbit
decaying and re-entering our atmosphere...there's over 10,000 pieces
of 'stuff' in orbit now counting everything...spent rockets,
third stages, defunct old satellites, etc.

They (meteors) come in all sizes and all speeds and all brightnesses,
and all directions from horizon grazers to zenith passes, and even
point (head-on) meteors....a bright spot in the sky that flares up
with no apparent movement, then just disappears. It's coming right
at you.  I've seen them break apart in flight into 4 or 5 separate pieces, disappear for a moment, then reappear. End in a super-bright terminal burst that lights up the landscape like a flashbulb going
off for an instant....meteors that last for only a tenth of a second
to some that streak across the entire sky for 20 seconds, looking
like a jet fighter on fire all the way.

So that's my best guess, a meteor ending with a terminal burst.
Not unusual at all, but relatively scarce as most don't do that.
And if the terminal burst is extremely bright, then we call it
a bolide.
Clear Skies,
Tom Whiting
Erie, PA

PS..Oh, we try to avoid the terms 'shooting or falling stars' in
astronomy, as these objects have nothing to do with stars. The preferred terms are meteors, fireballs, or bolides, depending on the brightness and type. A bolide ends with a bright terminal flash,
and a fireball is a meteor that's brighter than Venus, and/or remarkable enough to make the newspaper and news the next day.

---------- FOLLOW-UP ----------

QUESTION: Thanks Tom. I searched the web for months for an answer. Very cool.
Q: I have been lucky enough to witness 2 fireballs in my young life. One of them was amazingly brilliant and looked like the size of a car flying less than a mile overhead. Is there a way/formula to determine an area to look for it?

Answer
Hi again Daniel,
While the fireball in question may have looked very close and bright,
most of those meteors are burning up from 100 to 60 miles high.
Rare indeed is the meteor that makes it down to even the 20 mile
high point. So the odds are quite good that it completely disintegrated way before ground impact, or it just simply went 'over
your horizon' no matter how big and bright it looked to you.

Realize the typical meteor is a grain of sand size, or even cigarette
ash size and consistancy.  A pea-sized object is a very bright meteor, and a walnut-size makes for a very bright fireball or bolide. (Probably the ones you witnessed). None of these make it to the ground.  Almost all the light you see isn't mass, it's velocity, like 10 to 100 miles per second.
Recall the kinetic energy formula; energy equals 1/2 mass times velocity squared, so what you are really seeing is conversion of velocity squared... to energy, and not the mass component, which is nearly negligible.  (You'd completely burn up and explode too, if you hit the atmosphere at say, 20 miles per second!)

For meteors that become meteorites and actually impact the ground,
one has to mathematically triangulate to find a ground position,
so one has to have at least 3 accurate sightings widely separated
and go from there.  Just one sighting will only give you a single
"line of position" like in navigation, so one has to have 3
accurate sightings to find where 3 lines of position cross, to
accurately locate any impacting body.
So that's the method they use, triangulation for the position.
Clear Skies,
Tom Whiting
Erie, PA