2012/9/14 George Herbert <george.herbert@gmail.com> > > Also , did a search of Seesat's archives (thanks George) and only 1 hit > from 53 weeks ago by > > Kevin Fetter http://www.satobs.org/seesat/Sep-2010/0198.html , > although Satflares newly > > expanded DB showed this report by Brad Young early this year also . > > http://www.satobs.org/seesat/Jan-2012/0228.html > > > > Question - does the database show it in umbra or penumbra at that point? > > The sun's not a point source, and this could be where a simplification > is getting that point wrong... > > To my knowledge, no formal reports contain info on penumbra. Many years ago I made comparisons of shadow entry/exit positions by some satellite prediction programs. There were large differences, not only caused by selecting umbra/penumbra point. Rob Matson's SkyMap was the most compatible with reality, and also shows the penumbral part in a different colour. Previously on the same thread : Flares/flashes by the Moon (and penumbra!) share the characteristics of solar flashes, since the Moon is roughly the same size. But even the full moon is about 15 magnitudes fainter than the Sun, so its flashes are at most magnitude +7 ! And at the time, the Moon was far from full. Planets is a different case - when we see a solar flash from e.g. an Iridium panel of 1.5 sq.m. at 1500 km range we see a part of the Sun. Its apparent diameter is 32', Jupiter 41" and Venus now 18". The flat apparent Sun disk at this range is 1500000m/110 diameter, about 13500 m, ie a surface of 150000 000 sq.m. This ratio (if the reflection is specular and 100% albedo) makes the flash about 20.0 magnitudes fainter than the Sun. But for Jupiter and Venus we would see a larger percentage of their disk reflected, giving a magnitude loss of about 11.7 and 10.0 magnitudes - now to +9.5 and +6.0. It might be possible to see them, but the width of the flare track, corresponding to the solar flare 13500 m at this range would correspondingly smaller, much smaller then the orientation accuracy of an Iridium, and of course completely unpredictable for debris. /Björn /Björn -- ---------------------------------------- Björn Gimle, COSPAR 5919 59.2576 N, 18.6172 E, 23 m Phone: +46 (0)8 571 43 312 Mobile: +46 (0) 704 385 486 -------------- next part -------------- An HTML attachment was scrubbed... URL: http://mailman.satobs.org/mailman/private/seesat-l/attachments/20120915/f46c83f2/attachment.html _______________________________________________ Seesat-l mailing list http://mailman.satobs.org/mailman/listinfo/seesat-l
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