Saturday, April 5, 2014

Streaks in the Sky!

I've long advocated using Heavens-Above for tracking not only the appearances of satellites in the sky, but it is helpful for making star maps for a particular date and time, and for tracking the location of planets and comets.  This weekend I'm helping out at Kitt Peak National Observatory's intro class in astrophotography, and when I saw there were a couple satellite appearances, of course I had to try to capture them!

First up, about an hour after sunset, was an Iridium Flare - a glint of sunlight off the antenna of one of the Iridium constellation of satellite phones. Since they maintain an accurate orientation in space, Heavens-above can calculate when their flat, shiny antennae shine a shaft of sunlight across a narrow path of the earth. These glints can become quite bright and for brief periods become the 3rd brightest thing in the sky. From Kitt Peak last night, we were about 6 miles from the center line, but was still to be nearly as bright at Venus at -4 magnitude, and just above Polaris. I found a vantage point looking north that included the 4-meter telescope, the flare and the Big and Little Dipper asterisms. Right on schedule (you can set your watch by these!) it flashed the sun down on us, and fortunately, the shutter was open! I had anticipated a longer exposure to get more of the Iridium's trail, so turned down the ISO and F-stop a little and ended up only getting the flare. It was ok s the stars came through fine, as well as some of the lights along I-10 and the lights of Tucson reflected in the clouds. Besides the bare-naked image at left, an annotated one at right shows the asterisms.

After the Iridium flare, I had 20 minutes to find another vantage point for a pretty good International Space Station (ISS) pass.  ISS, the largest satellite assembly orbiting the earth, is easily seen shortly after sunset or before sunrise when it is dark at the observer's location, but the sun still illuminates it circling overhead.  I decided to hike up around the 4-meter to record it passing to the south of Kitt Peak.  Once there, I realized the moon couldn't be in the shot, so set up in the shadow of the 4-meter dome for the passing.  Again, like clockwork, ISS appeared and passed with its contingent of astronauts on board.  The clouds added an interesting element to the image, and rather than the single vertical frame, I decided to take 2 more images and combine them into a horizontal mosaic.  So this image is a combination of 3 frames with my wide-angle 10-22 zoom set to 12mm.  Assembling the 3 frames with Microsoft's ICE (Image Composite Editor), there is naturally some distortion, but shows the ISS pass below Canis Major past Jupiter over the 4-meter dome past Auriga to Perseus, as well as a few of the moonlit domes on the mountain.  I've got to admit that ICE did a great job assembling the frames - even with the 3.5 minute exposures (plus 3.5 minute in-camera darks), I don't see any errors, artifacts or gaps given the time gaps between frames...

Another classroom session tonight - I give my presentation on time-lapse imaging.  We'll see if another imaging opportunity crops up...

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