Tuesday, March 20, 2012

Marking the First Day of Spring!

One of the fun things to do on clear nights, even in urban areas, is to look for Iridium Flares.  Just think - spacecraft the size of a Volkswagon is angled just right to shine a shaft of sunlight down where you happen to be standing!  Because these spacecraft (an array of satellite phone transponders) maintain a known attitude as they circle the earth, it is straightforward to calculate when they reflect the sunlight.  My favorite website for this is Heavens-above - you just enter your place on the earth via Google Maps or entering the name of your town (being sure to enter your proper time zone), it will tell you when and where to look for these "flares" that last for a good part of a minute.

I happened to notice last night that one would appear tonight at about 7:30 here in Tucson, and if we moved just a couple miles to the west it would brighten from magnitude -4 (about the brightness of Venus) to -8 (about the brightness of the quarter moon)!  So we setup at Jacobs Park near Prince and Fairview to image it.  I used my camera with an 8mm fisheye to catch a wide field of the northern sky that also included a bit of twilight and Jupiter and Venus in the western sky.  With Min's camera we used the 10-22mm zoom set to 17mm to catch the flare between the Dippers.  Because we wanted to expose for the entire appearance, but didn't want to overexpose it in the still-twilight sky, we dropped the ISO to 100 and F-stop to F/5.6 for each and set the exposures to 90 seconds.  Because these flares are accurate to the second, we just opened the shutter 45 seconds before the mid-flare time (before it was visible to the eye), and hope for the best.

Unfortunately, there were a lot more lights from nearby soccer and baseball fields than I thought from my afternoon scouting trip.  We found the darkest part of the park, focused on bright planets or distant lights.  We finished setup with seconds to spare, and started the exposure at the predicted time.  Right on schedule, the satellite brightened, flared very close to the predicted -8, then faded out.  I'm sure that even with the dozens of people near us at the park, we were the only ones witness to the event.  It was still fun to watch, and witness a little of the sky on a clear night. 

Sure, it would have been more impressive from a dark sky, but it also would have been easily visible by stepping out our door and glancing up at the right moment.   And while it is merely a passing piece of hardware with a shiny mirror reflecting the sun down to your eye, we highly recommend hunting them down and checking them out.  The public at the Grand Canyon see us as mystical shamans for being able to predict these majestic lights in the sky - you may well be amazed as well!

1 comment:

David A. Harvey said...

Nice shots Dean - I saw the same flare - it was -8 mag from my side of town. Brought the whole family outside 30 seconds before the flare - told them to look to the north at about 45 degrees up and I would make a "star explode ..." such are the warped powers of a demented amateur. :-)