Hello, Sky and Telescope December 2002 publishes, page 143, a picture by S.M. SABATINI showing an Iridium flare reflection on the River Colorado in Arizona. I send to the author my best congratulations. That is the picture I dreamed of for many years, tried again and again and never succeeded. This question had been widely discussed on this list under various subjects particularly " Iridiums Flares ground projection" ( february 98 ) and " Zigzagging flare coordinates " (may 98) and I took part of it. Rob. Matson, Bjorn Gimle and many others wrote on this subject. Here is a small extract : >RJ@RMATSC.RIEM.COM schrieb: > The width and length of a perfect Iridium flare can be calculated as > follows: > > dist = distance from the observer to the sat > alt = angle from observers horizon to the sat > 1/2 = angular diameter of the sun > > width = dist * tan(1/2) > length = width / sin(alt) > > For an Iridium whose distance is 1200 km and 30 degrees > above the horizon the flare width would be 10 km and > length 20 km. > > Real flares are far from perfect however. There is no sharp line > between light and dark and the actual flare spot would be both > larger and fuzzier. > > The velocity of the flare is much harder to calculate but it would > be of the same order as the velocity of the spacecraft. > I got the impression that almost everybody thought my aim of photographying a flare from a hill, reflecting on the sea surface close to the shore, was a mere utopia. The success of S. M. Sabatini shows at least that I was not completely wrong and that the width of the light line seems far smaller than 10 Km. Why did I not succeed ? My explanation is as follows : Because of my location I pointed my camera to the place where the projection of the flare would appear on the sea (to the North-West) while the satellite would flare in the sky from the South West. SM Sabatini has succeeded because he pointed to the satellite and to its reflection at the same time, and ACROSS THE WATER PLANE. That is my impression, but I would ask advice from the members skilled in optics and mathematics. Is the light projected by the iridium antenna really a beam ? and what is it like in 3 dimensions through the space ? Jean Monseur N 49.305 W 0.067, Alt 74 m Cliff along the English Channel Shore, France. ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www.satellite.eu.org/seesat/seesatindex.html
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