Monday, May 10, 2010

-5 KeyHole flare! (May 9th observations, Part I)

Yesterday evening (9 May) I observed the most spectacular Keyhole flare I have ever seen. KH-12 USA 186 (05-042A) flared brilliantly to at least mag. -5 in a blue twilight sky, while crossing from Cvn into Uma. It yielded this Iridium-like picture:

click image to enlarge

I cannot provide a brightness profile: for the simple reason that the trail is saturated over the full length. Peak time was about 20:34:29.4 UTC (9 May 2010).

I also observed on the 5th and 6th of May, capturing a.o. USA 186 again, as well as the IGS 5 r/b and the Molniya object USA 198.

USA 198 (07-060A) showed a clear, slow brightness variation over the 1m20s image series of 5 images, taken on May 5th, growing slowly fainter over the series:

click images to enlarge

The data during the first 12 seconds of the diagram above, are close to saturation. Hence, the brightness variation in reality is probably more expontential than the diagram suggests.
The background readings have been taken just to the right of the trails, and are plotted to show that the change in brightness of USA 198 is not due to lens vignetting, but real.

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