Wednesday, 22 March 2006

Lacrosse 4 Flare and missing Lacrosse 5

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Conditions were poor this evening: haze due to very thin high altitude clouds lowered the limiting magnitude considerably. Still, some work could be done. And I was rewarded for the effort with observing and imaging a nice short-duration magnitude 0 flare by Lacrosse 4 (2000-047A, #26473). The image above shows the flare: the start of the trail coincides within a second or so with peak brightness, and the satellite then can be seen fading rapidly. Stars visible are in Leo.

Only the bright start of the trail was measurable and hence yielded one point. It is 0.3 seconds early with regard to Mike's 9 day old elset 06072.38962997. It corresponds quite well in delta T to the series of positions on 2000-047A obtained by Scott Campbell 20 hours earlier (delta T also -0.3 sec). Both Scott and mine are however a few tenths of a second different in delta T from a position reported by Russell Eberst, while a position Lutz Schindler reported only minutes after my observation is different by as much as 2 seconds in delta T. Which shows the human factor in this work.

That became evident in another way this evening too. I tried to observe Lacrosse 5 during its 19:30 UTC pass and failed to see it. This while Philip Masding from the UK and Lutz Schindler from Germany did see it only minutes before and after my attempt! Maybe it were the observing conditions, although I really would have expected to see Lacrosse 5 at its usual brightness of mag. +2, the more since I was able to see Lacrosse 4 at a similar brightness (before it flared) 20 minutes later.

Update: Pierre Neirinck from France reports he initially couldn't see it either on that pass, eventually picking it up rather late at 19:33 UTC. So he believes Lacrosse 5 did its "disapparance trick" again between the observations of Philip and Lutz.

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