Being an active visual observer, I spend a lot of time outside at night at the eyepiece of my telescope dealing with the weather, the moon, unwanted light sources and wildlife that happens across my path.
This week I plan to write a series of pieces about my encounters with animals in the dark while pursuing my astronomical interests. If you'd like to read them all, simply click on "Animals in the dark" under Simotopics and the whole series will come up.
This first story is from several years ago, while I was actively monitoring cataclysmic variables (CVs) for outbursts. On a typical night I would race from one field to another, checking on stars in my program and logging an observation about once a minute or so. I'd start in the west and work my way east across the sky, checking each field for a sudden brightening, or outburst, of a CV. My goal was to monitor as many fields as possible, and I'd try to do at least 100 per night. The other part of the process is, when you do not detect an outburst you need to report the faintest star you can see, to provide an 'upper limit' on the magnitude of the variable.
If the sky conditions were good, I could see as faint as magnitude 14.9 with the ten inch telescope I had at the time.
On this particular night I had been observing for about an hour and a half, when suddenly I pointed the telescope to a new field using the finder scope, looked into the eyepiece and saw nothing. No stars, just a hazy darkness. It was a perfectly clear night when I began and now I couldn't see crap!
When you observe from inside a dome you don't always notice weather or clouds approaching, and I've been surprised many times stepping out of the observatory to see that the whole sky has suddenly clouded up on me. So naturally, the first thing I did was to step outside to see if the sky conditions had suddenly deteriorated. Happily, the sky was still perfectly clear with no signs of passing clouds or approaching fronts.
Thinking that maybe I had just been getting tired and needed a break I stayed outside, breathed in the fresh air and enjoyed the view for several minutes. Once back inside the dome, I checked the finder scope to be sure I was pointing where I wanted to be pointing, and then looked into the eyepiece again. Still nothing.
I checked to be sure the eyepiece hadn't got fogged or frosted over, I tried refocusing, nothing worked! As a last resort I aimed the telescope down to where I could examine the corrector lens on the front of the scope to see if the dew heater had quit and the lens had fogged over. I couldn't believe what I saw next.
There, covering probably 80% of the lens, was the biggest gob of bird poop I had ever seen in my life, complete with the remains of some partially digested blue berries. What I can only imagine must have been some giant condor, at the precise moment I moved the dome slot and re-aimed the telescope, had silently dropped a huge splattering mess, like a smart bomb, right through the slot and delivered a bulls-eye strike to the lens of the telescope.
The problem wasn't that I couldn't see crap; it was that I couldn't see through the crap!
That was the week I learned how to clean the corrector plate of a Schmidt-Cassegrain. But that's another story for another time.