Saturday, August 15, 2015

Meteors and star trails

A fluorescent lichen glows on a tree trunk, late last Thursday night. It is Pyxine subcinerea, which fluoresces quite brightly under a black light, which is exactly what it's doing here. Expert lichenologist Ray Showman was holding the light so that I could make the image. In a fit of good lichen luck, its sister species, Pyxine sorediata, is just to the left (the slightly larger round lichen crust in the upper lefthand corner). It does not fluoresce. Lots of strange and interesting things are visible at night.

I was down in Vinton County, Ohio last Thursday to speak to the Four Seasons Garden Club, which Ray's wife Carol hosted at their lovely home. While that was fun, I saw an added opportunity. Thursday night's skies were to be totally clear, the moon was new, and it was the tail end of the Perseid Meteor Shower. All the conditions were prime for astrophotography. Vinton County is also one of the least populated (the least?) counties in Ohio, so ambient light pollution from towns and cities is much less than in most areas.

As Carl Sagan might have said, billions and billions of stars speckle the sky. After Ray and I spent time exploring, had an excellent dinner courtesy of Carol, then poked around a bit after nightfall, I crashed for a few hours. I was back up at 1:30 am and outside to set up the camera rig and try shooting for the stars.

The night sky at this spot was breathtaking. The Milky Way was clearly visible, its myriad stars forming a hazy smear across the night sky. Various constellations and planets popped in sharp relief, and an occasional satellite would move rapidly across the ether. In all, I was out for about 3.5 hours, watching, and making occasional shifts to the camera gear. A nearby Yellow-billed Cuckoo called often, usually delivering a soft truncated series of junglelike kowlps. I wasn't surprised to hear it - cuckoos routinely call at night. It may be that they're actively hunting, as caterpillars are a major prey source and most caterpillars are far more active at night. At one point, an Eastern Screech-Owl created a series of spooky whistles, and I heard distant Coyotes.

As always, click on the photo to enlarge

Catching meteors flaming out as they streak across the sky is largely a matter of luck. I saw dozens, but most were too far to really show up in my images. A few, however, did. Several fireballs did shoot by and were spectacular, but they weren't in my camera's field of view. I would have had a killer shot, but blew it in a total learn from your mistakes experience. After a few hours, I switched to a very fast 70-200mm f/2.8 lens, set to 70mm focal length. This greatly reduces one's chances of capturing a meteor as the field of view is much smaller than the wide-angles normally used. But if one does streak through the field of view, you'll likely have a really cool shot. And one did, and it WOULD have been an amazing image. Except, I forgot to turn off the lens's auto focus, and image stabilization when I mounted it. Not doing so means the camera hunts and pecks and everything is blurred. Including my meteor image. Duh. Well, I hope I won't be making that error again.

A composite of 152 images stitched together, which encompassed slightly over an hour of night sky, creates a swirling vortex of star trails. Polaris, the North Star, is at the center of the vortex. Because Polaris is at due north, it appears stationary in the sky, while the other stars appear to rotate around it. The dashed line running diagonally across the lower lefthand corner is a jet trail. I thought I was going to get through the entire hour-long shoot without a plane flying across, and I cursed when I saw it coming.

For these shots, I used my Canon 5D Mark III tethered to Canon's excellent 24mm f/1.4 lens. This a major go-to lens for shooting astrophotography, because the aperture opens so wide and allows lots of light to reach the camera's sensor. The 24mm focal length is fairly wide-angle and captures a nice swath of night sky.

A tripod is utterly essentially for these supremely long shoots and long exposures. As is a remote shutter release that locks in place so that the shutter keeps firing continuously until you make it stop, or the battery dies, or the memory card fills. My shutter speed was set to 25 seconds, and the aperture was set to f/1.6. The ISO was at 400. Before locking down the shutter and letting her run for an hour or so, it's essential to take a few trial single exposures and tweak the settings. Also, framing the sky is important and not that easy to do. I use an app on my iPhone that identifies the major stars and constellations. By holding its map of the night sky over my camera barrel like a gun sight, I can be sure of what I'm looking at as I frame the shot. Make sure your lens's auto focus and image stabilization is TURNED OFF. Also, I set my white balance to tungsten, as I like the slightly electric-blue cast that it gives celestial objects.

I made a short video which is a compilation of all 152 images which went to make the previous photo. For some reason, YouTube won't let me embed it right now, but you can see it RIGHT HERE. If you watch the video in full screen mode, you'll see a number of distant meteors shooting by in various directions. A real scorcher shoots right through the screen near the end.

1 comment:

Bruce Lindman said...

Edit out the jet trail from the few frames in which it appears before creating your star composite. That's what I do. Also, satellites and such.