Voit lisätä twiitteihisi sijainnin, esimerkiksi kaupungin tai tarkemman paikan, verkosta ja kolmannen osapuolen sovellusten kautta. Halutessasi voit poistaa twiittisi sijaintihistorian myöhemmin. Lue lisää
1/13
A fireball over California on 30 Jan 12:30 UT (22:30 PST) is deemed a "#spacedebris reentry" by @amsmeteors:
https://www.amsmeteors.org/2020/01/space-debris-re-entry-caught-on-allsky6-cameras/ …
I do not agree with this assesment.
A consolidated thread on why I think this likely *isn't* a reentry:
2/13 First: I acknowledge determining an origin from single video records or visual observations only can be difficult. Yet, some pertinent info can be gleaned from single video records. One of these is angular speed (you can measure this) and duration.
3/13 From video of this fireball, my immediate thought was "this looks too fast and too short duration for a reentry". It was visible for some 15-20 seconds during which it traversed a considerable part of the sky. Space debris typically takes longer and is slower than that.
4/13 Space debris reentries typically take minutes, and have low angular speeds. The 20 seconds would be very brief for a space debris reentry, and on the video it can be seen to move over a large part of the sky in mere seconds.
5/13 From a video caught by the all-sky camera of Bob Lunsford near San Diego (https://youtu.be/rF2-OD44Jp0 ) and stars visible in that video, we can determine the angular speed of the fireball in the sky: it moved about 35 degrees in 6 seconds, or 5-6 degrees per second.pic.twitter.com/OA2ectG2EA
6/13 That angular velocity is too fast by a factor of two for space debris at this elevation. Satellite orbital speed is determined by orbital altitude & leads to predictable angular speed. To show you, I constructed a 70 x 110 km reentry orbit matching the video trackpic.twitter.com/BimzuJCGeH
7/13 As can be seen (previous tweet), reentering space debris in such a trajectory should have an angular velocity of no more than 15 degrees in those 6 seconds - not 35 deg as was measured for this fireball (i.e. it should have moved about 2.5 deg/second - not 5-6 deg/second).
8/13 So this object would seem to be *too fast* by a factor of two. As reentering satellites have a typical orbital speed of 7.9 km/s, this would point to something in the 12-15 km/s class. That is the speed of an object in heliocentric orbit - a slow piece of asteroidal debris.
9/13 Looking at CSpOC satellite tracking data, there is no apparent reentry candidate for this date and time. This while a "satellite reentry" this bright should be a big object - this is not the "nuts and bolts" category. It is unlikely that CSpOC would have missed that.
10/13 Note that meteoric fireballs (small pieces of asteroid or comet entering our atmosphere) are still more common than space debris reentries. Also, slow asteroidal origin meteors can & often do fragment profusely - e.g. the Peekskill meteorite fall:https://youtu.be/4_orvF9bLZg
11/13 20 seconds duration for a slow asteroidal origin fireball is certainly not impossible - especially during a grazing entry. It however would be unusually brief for a space debris reentry, which typically takes minutes, especially when it concerns large objects.
12/13 So, in summary: 1) angular velocity appears too large; 2) duration, while long, appears too brief; 3) and there are no reentry candidates; ...making it unlikely for this to be reentering space debris
13/13 But: 1) angular velocity okay for a slow meteor; 2) duration not impossible for a meteor; 3) ubiquitous fragmentation occurs with slow asteroidal meteors as well. So in my opinion, all the evidence points to a slow, fragmenting meteoritic fireball, rather than space debris.
Twitter saattaa olla ruuhkautunut tai ongelma on muuten hetkellinen. Yritä uudelleen tai käy Twitterin tilasivulla saadaksesi lisätietoja.
