**Previous message:**Björn Gimle: "Re: Simultaneous Iridium flares"**In reply to:**Björn Gimle: "Re: Simultaneous Iridium flares"**Next in thread:**Edward S Light: "Re: Simultaneous Iridium flares"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ]

Thanks all. There is no way I can prove anyone's maths wrong - way beyond my level of expertise. I have had difficulty getting Iridflar to work - not sure whether this is my problem or the system's. Incidentally Björn you also posted helpful information to the observer of the twin flare in 1999! Robert Robert. ----- Original Message ----- From: "Björn Gimle" <b_gimle@algonet.se> To: <SeeSat-L@satobs.org> Sent: Thursday, March 27, 2003 2:59 AM Subject: Re: Simultaneous Iridium flares > > Using IridFlar and the current elset at Mike's site, I get the range > difference as 1665.6-1391.3 = 274.3 km and a flare center diff of 3.8 > seconds. > > Using SkyMap, their vertical separation was 800.0-693.3 = 106.7 km. > > There are 17 satellites marked ? (engineering "spare" orbits - I am > surprised that HA predicted one of them) in iridium.tle. Their Mean .> Motions are 14.36-14.93, vs the operational 14.34215. > This means that each one of those 17 will overtake one of the 11 in the > same plane 0.24-6.49 times per day, in total 47.6 encounters per day. > > Actually, the higher the frequency, the shorter the duration of each > encounter. > "Your" Iridium 94 ? flare ground speed differs from the Iridium 28 ground > speed by about 0.27 km/s. If the definition of "close" is +- 1 s, this is > about 15 km, or 56 seconds. > Since Iridium 94 ? passes an operational one 3.56 times per day, there is > a close pass 3.3 minutes/day somewhere on Earth. > > This duration (longer but less frequent, or in one case shorter but more > frequent) times 17 is almost one hour out of 24, or about 24000 km in > total. > > The width of a good/visible flare depends on the elevation, say 150 km at > night, 10 km in daytime. > The length of the flare track may be almost the full orbit for twilight > orbits, a half orbit for "noon orbits" at 10 km width, and perhaps 1/10 > orbit at 150 km width. At any time, there may be nearly two MMA flares > hitting the ground, on the average ?? > > Assuming an average (150,5,15 km) of 25 km, I get 600 000 square km > covered by double flares each day. The Earth is 510 000 000 km, so each > should have a one-second coincidence in three years. > > Please prove my math wrong ! > > One way is to run a large number of two-month runs with IridFlar, > covering one or more years and a number of latitudes, and let a program > count the number of coincidences (or coincidences within a minute and > divide by 60). > > > > I have not had any response to my query so far. However I have done a > web > > search and can find no mention of any flares in such close proximity > since > > 1999! There are a few reports of double flares but these have been > much > > greater than 1 second apart. > > > > I would also appreciate it if someone could calculate the separation in > km > > or miles - it seems from the respective orbits that it may have been > less > > than 100 km. I guess I should have stated my elevation in feet or > metres > ... > > > This evening 25 March at 20:15 local (UTC plus 12) I observed with > the > > naked > > > eye simultaneous Iridium flares from a location at Wellington > waterfront > > > (41.2861 S; 174.779 E at 0 degrees elevation.) > > > > > > These were from Iridium 28 1997-051-E and Iridium 94 2002-005-C > > > > ... > > > > > > I would be interested to know how rare or otherwise sightings of > > > simultaneous flares are. > > > > > ----------------------------------------------------------------- > To unsubscribe from SeeSat-L, send a message with 'unsubscribe' > in the SUBJECT to SeeSat-L-request@satobs.org > List archived at http://www.satobs.org/seesat/seesatindex.html > > ----------------------------------------------------------------- To unsubscribe from SeeSat-L, send a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@satobs.org List archived at http://www.satobs.org/seesat/seesatindex.html

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