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Adventures in Forensic Astronomy

Annular-Total Eclipse, 30 May 1984

In November 2004, while ruthlessly purging videotapes from my shrouded past, I came across this VHS tape of a solar eclipse from twenty years before. As I recall, the images were jittery as the equipment stability factor was a bit low. But the overall experience was fantastic.

Fast-Forward into the Past

On May 30, 1984 some friends and I made our way to the Lake Hill Restaurant in Alexander City, Alabama. Our goal was to record an exciting solar eclipse. Dozens of observers from all over the world converged on this spot and others along the path. The fact that the Sun would be over 99.7% covered made this a rare annular-total eclipse. While not as spectacular as a full-blown total eclipse, this one was filled with opportunities to closely watch slivers of sunlight move in and out of the mountains and valleys of the Moon.

eclipse_prep00 (19K)

We used two sets of gear to record the event. One featured a tripod-mounted video camera staring down an ordinary refracting telescope with projection screen. Both had to be guided by hand, vewwy, vewwy carefuwlly. By me. Uh-oh is right.

And yet it seemed like child's play compared to handling the other Contraption, which consisted of a giant wooden L bracket on a tripod, supporting a pair of binoculars, a flat mirror, a video camera, and a projection screen. The whole thing was wrapped in black cloth to subdue reflections and increase contrast. It looked less like a solar 'scope and more like a Middle-Ages catapult. If The Demons needed to be chased away from devouring Our Sun, we were ready.

Naturally, just before eclipse maximum, the refractor's worm gear guiding mechanism reached the end of the track and I had to try to nudge it along by hand and keep the image somewhere close to the screen. Some frames made it, some didn't. But we captured a few frames that were usable, and had precise WWV time code on the audio track. My friend Chris Carey and I forwarded the tapes to the Naval Observatory anyway in hopes they could make use of them for precision measurements of the Moon and Sun.

The Contraption's images were not very useful. Oh, well. At least we had the most INTIMIDATING scope on site.

Can this video be saved?

Now, back to modern times. Just for grins, I dumped a few frames of the video into the PC and tried a little casual image processing. Choosing eight frames, I hand-aligned them, stretched the histogram and stacked them in an effort to reduce the noise. The results were surprising.

refractor_frame_403 (29K)

The left hand image is noisy, and cleaning it up would be a real chore at the time the tape was made. The image on the right is better than we had hoped for. The procedure, using PaintShop Pro or your favorite image editor:

  1. Choose an even number of consecutive frames. I chose eight, and with a 30fps video it's the rough equivalent of a 1/3 second exposure.
  2. Adjust the histogram for each frame to get the maximum contrast available.
  3. Stack and align the frames, giving equal opacity to each.
  4. Flatten the image.
  5. Use unsharp masking until the sharpening process introduces artifacts, then back off a bit.

The amount of noise reduction and the increase in detail is very pleasing to me, especially since I just did it by hand without the aid of software such as Stacker.

contraption_frame_474 (28K)

Even the murky raw images from the Contraption were improved. The procedure was the same as before.

refractor_frame_470_stacked (29K)

Yeah! Now this is what the Naval Observatory researchers wanted to see! Precise timing and location, coupled with detailed flashes of light dancing all around the ring. The main phase of this eclipse lasted only 13 seconds, but the sparkling lights known as Baily's Beads were visible for several minutes before and after.

The Mystery Tape

refractor_eleventwentyeight (23K) ch13_elevenfiftyfour (19K)

I also found one mystery tape in the pile of cassettes. Actually, it was just poorly labelled. I had only a foggy recollection that it was a duplicate of a tape given to me by a Birmingham TV cameraperson to forward to the USNO with our recordings. I'm sure at one time we knew their observing location. But it was a good quality, if slightly smaller, image, and it was well timed with a WWV soundtrack. A little reverse logic might pin down the location.

(Detailed map goes here. If you can read this I haven't gotten around to sticking it in the page. Until there is one pretend there's a map with the location of the TV truck discussed above.)

On the mystery tape eclipse maximum is about 25 seconds behind that at the main location in Alex City. The TV truck likely stopped somewhere off US431 and set up their gear. Not so hard to reconstruct, no?

The main path moved over many populated areas in the Eastern USA, and there are plenty of other web pages devoted to some spectacular photography of this eclipse. Several observers recorded prominences and a few even claimed to glimpse the corona, something very unexpected during a non-total eclipse. I'll throw some links up on this page as time permits. I just wanted to get my little handiwork out on the web.

And now back to the task at hand: archiving old brittle VHS tapes and tossing the goofy things. Bah!

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