Dear Frank Reed, Wonderful article.Even a child can understand the phenomena.Just incredible. best regards, DDPurohit On Mon, Mar 2, 2015 at 1:20 AM, Frank Reed via Seesat-l <seesat-l_at_satobs.org > wrote: > You wrote: > "Does this group have any assessment about what this could have been - if > it's a reentry? > The incident occurred over central parts of Kerala (roughly, 10 degrees > North, 76.5 degrees East) at about 10 p.m. India time (4:30 p.m. UTC) on > Friday, 27th February, 2015." > > There's no evidence that I can see that this was a re-entry (of an > artificial satellite, a rocket body, or other manmade debris). I have seen > two videos that appear to be actual footage of the object in question. They > show an event of very brief duration and high speed. Reports filed at > amsmeteors.org also indicate a relatively brief event. This matches a > natural fireball. By contrast, re-entering space debris (from a satellite > or rocket) would be travelling at a lower speed (low Earth orbital speed is > more than 40% lower than the slowest possible meteor/fireball speed) and > due to a relatively shallow entry angle would be seen travelling across the > sky for a great distance. The high speed and short duration argue strongly > against the space debris possibility. > > So what was it? The event can be described as "a relatively spectacular > fireball caused by the hyper-sonic entry of a small meteoroid in the upper > atmosphere dozens of miles above ground". There are thousands of fireballs > like this globally every year. Until recently, in the past five years > especially, fireballs were not widely reported, and those that were > observed remained "local news". The object that created this fireball would > have been a natural object, probably a "stone", on the order of one to > several meters in diameter entering the atmosphere at high speed and then > disintegrating due to the high temperatures and high dynamic pressure as it > slammed into the thin air many miles above ground. A small amount of > material would have reached ground though it's usually impossible to track. > Reports of shadows cast by the fireball as well as some reports of sonic > booms (reported as "tremors") and indications that it was brighter than the > full Moon suggest a larger object. > > A fireball is not rare in the global sense, but it is quite rare for any > indIvidual to see such a spectacular fireball (since each of us spend so > little time looking at the night sky). For a comparison, if we hold a > lottery every week and sell 100,000 tickets (with only one possible > winner), then the odds that any one individual would win are very low even > if you buy a ticket every week for a year, but the odds that someone will > win are 100% every week. Seeing a fireball is like a lottery: they are up > there, and if the event occurs over a populated region, the odds that the > event will be seen by someone are high, and yet for any one person it may > be a once in a lifetime observation. > > Be forewarned that many of the photographs that have been published by > various Internet "news" sites claiming to show this fireball over Kerala > are in fact stock photos. If you go to Google Images here > https://www.google.com/imghp and search on "meteor fireball", you will > immediately find two of the images that were used in stories about the > Kerala fireball. These images have been on the Internet for many years. > They were used simply to fill space in the recent articles. There are also > a number of videos that have been posted, e.g. on youtube, that are fake or > that display old footage or intentionally display footage of unrelated > re-entry events. This is common on Internet video sites since advertising > can be attached to videos which will generate a little income for the > poster regardless of whether the video is real or not. > > Reports of a "crater" seen in some media reports are also likely spurious. > Meteors enter the upper atmosphere at hyper-sonic speeds, but the brilliant > event that we see occurs dozens of miles above ground. By the time they > appear to "burn out" the speed is greatly reduced, typically to low > supersonic speeds, and by the time any remnants reach ground level they are > travelling at air-limited, subsonic "terminal velocity", a speed which > varies based on mass and size but is typically a couple of hundred > kilometers per hour for small stony objects. At such speeds, falling rocks > do not create craters, though they can create small "pits" in soft soil. > One might find a fragment resting in a small pit or hole, but not a large > bowl-shaped impact crater. Impact craters on Earth are never found except > with cataclysmic events precisely because the atmosphere nulls out the > speed of any small objects. As a result there are no actual impact craters > on Earth smaller than about one kilometer ! > in diameter. Reports of "charring" on the ground are almost certainly > unrelated. Since meteor fragments reach the ground at relatively low speed, > they are normally cold when they hit. In fact, because they were in deep > space minutes before, and since the heating of re-entry only affects a thin > surface layer, meteorites found immediately after impact have been found to > be icy cold. > > Frank Reed > http://ReedNavigation.com/aboutfer/ > _______________________________________________ > Seesat-l mailing list > http://mailman.satobs.org/mailman/listinfo/seesat-l > -- Divyadarshan D.Purohit Gurudev Observatory, Vadodara India http://www.gurudevobservatory.co.in/ https://www.flickr.com/photos/gurudevobservatory/sets/ _______________________________________________ Seesat-l mailing list http://mailman.satobs.org/mailman/listinfo/seesat-lReceived on Thu Mar 05 2015 - 01:42:25 UTC
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