Tuesday, August 14, 2012

Freshly Showered!

I've mentioned before that Tucson fully gets half of its rain in July and August, so normally those are months used to take a vacation from astronomical interests and get stoked for the clear, cool, dry observing to come later in October.  But August is also the best time for watching warm-weather meteor showers - the Perseids!  Sometimes you gotta try to get in some observing as clouds and storms allow.  Also, Melinda had never been out observing during a meteor shower, so she was looking forward to some sky-streaks!

This last Saturday, the 11th (12th, Universal Time), was predicted to be the peak of the Perseid viewing, and being that we were both sitting at home, we watched the weather carefully.  Of course, it was hot - 109F for a daytime high, and while not raining, it wasn't far away, with thick clouds hanging around.  Melinda brashly predicted it to clear by 10pm - her source - the Clear Sky Chart, a resource put out by the Canadian Meteorological Center commonly used by amateur astronomers for planning when conditions will be good for observing.  Well, it wasn't far off - we could see a few stars at that time, and by the time we hit the road about 11pm, headed for Geology Vista on the Mount Lemmon Highway, there were large patches of clear, with nearly perfect skies waiting for us at the nearly 7,000 foot elevation.  There were 3 or 4 cars already parked there, so we quietly set up a couple chairs next to the car and settled in for observing.

We didn't have long to wait!  While you should be able to see meteors anytime the apparent radiant is above the horizon, the higher in the sky it is, the more you will see.  Generally you see many more after midnight as well as the Earth's spin moves us more directly into the particle stream.  We started counting right at Midnight and they soon started popping across the sky, appearing to come from a point between Perseus and Cassiopeia very near the Double Cluster.  They were bright enough and numerous enough I set up a couple cameras to try to record some - a 14mm and a 16mm fisheye, both at F/2.8, mounted on tripods for 45 second exposures every 50 seconds.  Meteors are usually difficult to image - they always seem to appear away from where the camera is pointed!  But we seemed to be pretty lucky, catching some nearly right away, highlighted by the -5 magnitude one shown here at left about midway through our session.

Typical of many of the meteor trails we caught, the streaks start out with a greenish tint with this one undergoing three distinct brightenings as it burned up in the atmosphere.  This frame at left is the same as above, just cropped tighter to show more details of the streak and nearby galaxies identified in the annotated image above.   In the blowup, you can barely detect the trailing of the stars caused by the earth's rotation during the 45 second exposures.  I could have set up a tracking mount, but was a little more complicated than I wanted to get on this night.

The fisheye lens was set up a few yards away watching over the eastern horizon as the Pleiades and Vee-shaped Hyades star clusters rose into the sky.    In this view at left, a Perseid splits the Hyades star cluster.  Just to the left of the Hyades is the bright planet Jupiter, with the crescent moon partially obstructed by the thin clouds.  The rocks of the canyon walls are here lit up by the lights of Tucson behind and to the right of the camera.  The crop to the right shows again that the brightness varied along the trail, and it ended in a little pop as it was consumed in the atmosphere.

We ended up counting meteors for a little under 2 hours.  In that time, we counted 83 and caught 14 on the cameras during that time.  Since we were facing the same direction, we would have seen more if our views diverged, but we had a great time watching the natural fireworks!  I'm sure it won't take much arm-twisting to get Melinda to come out in mid-December for some Geminid watching...

1 comment:

David Allen Harvey said...

Great shots Dean! I really wanted to be top KP for the shower but was stuck in hospital. Sigh. Nice job!