(meteorobs) Breaking News - Major TX, OK, AR, MO, KS, CO, , NE Green, Fireball Meteor ~9:21CDT 23MAR2011

[Esko Lyytinen]

Hi,

I could find seven stars in the Oklahoma city camera sum image and ( to 
some degree with the help of earlier Sentinel camera derived imaging 
geometries) could calibrate this quit well.

I give here the start and end directions for also others to use, if of 
any use.
start az=292.60 , alt=24.305
end   az=262.07, alt=30.14
(with too many decimals)
I do not even have exact coordinates of this observatory, so for example 
an error of 11 kilometers in its location causes an 0.1 degree error in 
the star-postitions. But considering the image size, the real accuracy 
may not be much affected.

With these directions I went trough the previuos calculations, now with 
even more exact calculations and with the same expected start and end 
heights and assumed deceleration, I get the entry velocity as 15.5 km/s. 
With these assumptions It comes from directions 304.7 and slope 20.0 
degrees ( reference horizon and meridian is 35.0 N, 98.0 W ).
I have from the calculating Excel sheet automatic links to (somewhat 
modified) Marco Langbroek's Excel sheet for solar system orbit and I 
give here what it gives.
The apparent radiant RA   26.3 , dec +39.3
geocentric radiant      RA 12.4 , dec +30.7 .
heliocentric orbit:
a=1.66,
e=0.478
q=0.867
peri=126.7
node=2.944
( peri+node=129.65 )
i=7.67

If the end height would be 5 kilometers higher, this would decrease the 
entry velocity by about 1 km/s and shift the radiant on the sky by about 
3.4 degrees and of course the solar system orbit would have some change.

I might be thinking of possibly measuring some individual frames, but 
this I would like to do from the original size video, that I do not have.

But just an hour ago at 18:43:04 UT we had our own quite fine fireball 
:) At first impression this looks "smaller" but might have dropped a 
small meteorite, also this ? Now the study of this gets higher priority 
here, at least for a while.
Hope, I did not make any typos, in the values.

Esko

> Date: Sat, 26 Mar 2011 10:12:21 +0000
> From: Esko Lyytinen<esko.lyytinen at jippii.fi>
> Subject: Re: (meteorobs) Breaking News - Major TX, OK, AR, MO, KS, CO,
> 	NE Green, Fireball Meteor ~9:21CDT 23MAR2011
> To: meteorobs at meteorobs.org
> Message-ID:<4D8DBC05.1010901 at jippii.fi>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
>
> Hi all,
>
> With some experience (maybe some dozens of (derived at least small
> fragment) falls, and many non-falls of course) of determining dynamic
> (with also other) masses of Finnish and some others fireballs, I was
> thinking if to try to make a more thorough analysis if this, but because
> of yet non calibrated cameras (with now even no access to star data),
> this would mean maybe a week of full time work. So I did not start this
> big work, but made some quick rough "checking".
>
> I have earlier mapped the imaging geometry of some Sentinel cameras and
> used this data (assuming enough of similarity) to get the start and end
> altitude angle, with the assumed horizon location as a reference.
> ( I could quite easily get directions for Thomas Ashcraft camera, but
> this station was very distant, and the altitude angles near horizon
> (imaging geometry derived from star data) would not be as accurate as
> hoped for, so I did not measure these. Even this would need some star (
> or city lights) checking, if the camera directions have been fixed since
> calibrated. )
>
> The next is for the Oklahoma city vdeo.
> I get the start elevation as 23 dergees and the end elevation as 32 or
> 33 degrees.
>
> In the video, the duration is 9 seconds. And the fireball is allready
> visible in the beginning and also in the end.
>
> I ASSUME the true beginning height (in this camera) as 75 kilometers,
> (hopefully) consistend about to fit the rough velocity value, later in
> this. ( With a more sensitive camera and more nearby location (of
> start)n and considering that it is allready vislble, this would be a
> somewhat more high value with other circumstances.)
> Wit this I get the ground distance as 168 km ( the true accurate is of
> course not so good).
> ( Have in the calculations none or less rounded values.)
>
> IF we ASSUME the end height as 30 km, the ground distance to this is
> about 47 km.
> The meteoroid comes allmost towards the camera. With this assumption the
> ground path would be 121 km. But taking into accout the fact that it
> came a bit aside, this would be roughly 130.
> With this the average ground velocity is 14.5 km/s. Taking into account
> the slope (around 21 degrees, in these assuumptions) the average along
> the path would be 15.5 km/s. Noticing that it had deceleration, the true
> entry velocity might be around 17 km/s. ( could get a more elaborate
> value for consistency, but considering the over-all unecrtainty, may not
> bee needed.)
> This is a good case for this kind off check because of the limited
> possible "space" of the track.
>
> In the above, the end height  assumption is of course very uncertain,
> but IF it was more hight, this would mean a more slow entry velocity
> (and the contrary if more low).
>
> I can not get a good calibrated magnitude value, but think that this is
> well brighter that Iridium -8, so maybe -10 ?
> I try to get some integreted bightness value. I approximate maybe 5
> seconds at that mag -10 might give some level of an estimation (?)
> Better calibrated values are welcome.
>
> With the entry velocity and this value a formula for mass gives the
> entry mass as about 15 kg.
> ( I have not here the exact reference of this mass-formula, but this is
> from some oldish Canadian fireball-network publication. So this may not
> the best present date data, but is also about consistenet with our own
> derived dynamic masses.)
> Assuming the ablation coefficient as 0.01 and entry velocity as 17 km/s,
> that 15 beginning.mass would give the end mass about 3.5 kg ( fragments
> combined ).
>
> I also have my own non-published statistical formula for the masses and
> end heigth and slope. Data for this model is from oldish Canadian
> fireball-network pulication (table of derived end masses). And this
> seems to be more or less consistent also with my own dynamic mass
> determinations. For the data above (especially the assumed end height)
> this would give the end mass ass 4.5 kg.
>
> I could make some iteration cahnge with the end eight to get these two
> mass-values equal. This ( to get a real fit of the values) would mean a
> slight increase of the end height. But the general uncertainties are so
> big that there is not much sense to do this. The statistical model in
> the original data set was in almost all cases good to about relative
> values of 1/3 or 3/1 and the magnitude estimation (above) of this
> firball is very poor.
>
> We do not know the matherial of this instance, but also the Canadian
> data was not selected, although very probably mostly ordinary chondrites.
>
> Do not take that above as an actual trial of exact derivation of the
> mass. The true error margins are quite big.
> Its purpose is mainly to assume if this did fell a meteorite or not.
> I myself am quite confident, but NOT very sure, that this fireball did
> fell down a meteorite of "moderate" size ( from maybe about one to
> several kg range, if ordinary chondrite ), and (some) smaller
> fragment(s). Others may disagree, this is ok, of course.
>
> BUT, a low radiant angle, of course means a long dark flight. So even
> though (hopefully) getting the entry path well determined, the landing
> site location will not be so good.
> ( For similar size meteorites, lower entry agle also means higher
> luminous flight end height, that also ( in connection to the low entry
> angle) affects to lengthen the dark flight.)
>
> Regards,
> Esko