Re: [meteorite-list] Fireball dynamics questions:

[Rob McCafferty]

Here's what I know


 
 1a. Speed of sound at sea level? 1500 meters per second?
  

no, it's 340m/s


 
 2. What is the approximate maximum distance a ground
 observer can see fireballs over the horizon as limited by
 the curvature of the earth? my memory also says 250 miles

I remember deriving an solution for how far can an arial observer see across 
the ocean from different heights equation for someone around 4 years back. 
Light travelling in straight lines and all, the same derivation would apply in 
the opposite direction, for a ground observer looking at an arial object.

My calculations suggest that an object incandescent at an altitude of 100km 
could be visible from as much as 600km away. A fireball 6 miles up could be 
seen from as much as 160km. It'd be right on the horizon though so in reality, 
probably much closer if there are any hills or buildings. If it stops glowing 
while above the horizon, it will be closer. Directly overhead being around 15km 
or so. (see below)

250 miles fits in between both of these values.

 3. What are the approximate maximum and minimum altitudes
 where a meteoroid can incandesce?  130 down to 5 miles asl?

Atmospheric drag isn't really appreciable above 100km. 
Incandescence of a actual meteorite stops at altitudes of 30km - 5km. They will 
still be travelling at some speed at this height but not fast enough to ionise 
the air around them. Friction will continue to slow the meteorite




 4.  What is free fall maximum velocity assuming 0 cosmic
 energy remaining?  120 or 400mph?

Again, depends on the mass of the final object and shape of the meteorite. 
Stoke's Law can be used if modified (air being a compressible fluid) but you'll 
need to approximate the meteorite fragemts to a sphere. Not always practical.
Terminal velocity will depend on the mass of type of meteorite as well. It's 
between 120m/s and 250m/s for a fist sized rock of stony and iron meteorites, 
respectively
It's worth pointing out that unlike ordinary falling objects that start with a 
vertical component of zero and then increase in speed, a meteorite will start 
from high speed then reduce to terminal velocity at 6 miles and actually slow 
down further as it falls into thicker air. Considering the uncertainties in the 
other factors, though, careful consideration is unlikely to improve the 
accuracy of your predictions.


Rob Mc






  
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Re: [meteorite-list] Fireball dynamics questions:

[Sterling K. Webb]

Eman (Comic Book Hero, sounds like..), and List,


Beaten to the punch, but I got numbers...


 What is the approximate maximum distance a
 ground observer can see fireballs over the horizon?

The curvature of the Earth is roughly 61cm per
kilometer of curvature. If your eyes were 183cm
high and standing on a perfectly spherical Earth,
the horizon would 3 kilometers away. Conversely,
if you can see an object three kilometers away,
it has to be at least 183cm off the ground at its
location.

If a fireball lights up at 80 km elevation, it's above
the horizon for locations up to 135 km (in ground
track) away in all directions. And of course, the
Earth isn't a perfect sphere; standing on a mountain
looking out over plains adds to your distance, and
so forth. And a faster object would light up higher
than 80 kilometers. 80 to 100 kilometers is the usual
light-up altitude.


 Speed of sound at sea level?

343 meters per second (1,125 ft/s), or 1,235 kilometers
per hour (767 mph) at GROUND LEVEL. In the Earth's
atmosphere, the most important factor affecting the speed
of sound is the temperature. Temperature and thus the
speed of sound normally decrease with increasing altitude.


 maximum altitude where the atmosphere dense enough
 to support the formation of sonic boom?

At very high speeds and altitudes the Mach cone does not
intersect the ground and so, no boom is heard. Booms are
a lower altitude phenomenon. Got no precise figures for
you, though...


Sterling K. Webb
-
- Original Message - 
From: Mr EMan mstrema...@yahoo.com
To: metlist meteorite-list@meteoritecentral.com
Sent: Thursday, February 19, 2009 5:28 PM
Subject: [meteorite-list] Fireball dynamics questions:



I am still trying to assemble a trajectory and terminus for the Kentucky 
fireball of 13 Feb.  Lots of sightings but nearly all are missing critical 
data like azimuth.. duh.  I need some facts/values and can't seem to find 
them in the archives or my notes. My memory is not specific enough to use. 
(Metric or English is fine, I can convert when I rewrite my tables)

1. What is the approximate maximum altitude where the atmosphere dense 
enough to support the formation of sonic boom?  Somewhere my mind says 
32miles.

1a. Speed of sound at sea level? 1500 meters per second?

2. What is the approximate maximum distance a ground observer can see 
fireballs over the horizon as limited by the curvature of the earth? my 
memory also says 250 miles

3. What are the approximate maximum and minimum altitudes where a meteoroid 
can incandesce?  130 down to 5 miles asl?

4.  What is free fall maximum velocity assuming 0 cosmic energy remaining? 
120 or 400mph?

5.  To plot and publish results on google maps do I need to be a paying 
member?

Bonus Points: anyone have a contact/office name in the FAA to access air 
traffic Control radar tapes for a specific time and date? Anyone know the 
name of the Canadian Academic that was getting downgraded USAF fireball 
data?

Thanks,
Elton
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