We’re running a membership drive this month – our goal is 150 new members, which maybe is ambitious but we are adding a few new people every day, thanks! – and as a part of it we’re including this blatant clickbait series… Besides, it’s a chance to tell some of the funny stories that come up during cloudy nights at the VATT!
The old astronomer tells the tale… There were several groups at different telescopes on different peaks in the area, all looking to record the occultation of a star by Neptune. The goal was to see how Neptune’s atmosphere made the star dim as its light passed through first the upper, then the lower atmosphere.
Everything was working well. We’d had a guest with us earlier in the evening, but they couldn’t stand the early hours and had gone back to the dorm to get some sleep. They took the white flashlight with them, but that was OK; we normally use a red flashlight to keep our eyes dark adapted. Our job was to guide the telescope on the star, even as Neptune went in and out of the field of view. Just for good measure, we started things running well before the event, to get a good baseline for the star’s normal brightness.
Occultations are still the best way to measure the size of small objects like asteroids. This figure comes from the web site of the International Occultation Timing Association, IOTA, which tells you how to do it!Then came the phone call! Two of the astronomers “down the road” at another telescope had seen something unusual, a dip in the star’s brightness before it reached Neptune! Was it a real observation or just a glitch in their instrument? Well, that’s why we had more than one telescope looking.
Those were the days of chart recorders… which meant that rather than having to download a series of computer files you could just take a look at the strip of paper to see if there was anything to be seen. One of us ran over with her flashlight to take a look at the strip chart recorder. Unfortunately…
“Bad news,” she reported. “It looks like the strip chart recorder isn’t recording anything. I can’t see any line at all. Maybe something is malfunctioning? Maybe the pen ran out of ink?”
With the impending fear of a wasted evening, we hurried to see if we could fix the recorder before we missed the event. Turning on the white dome lights, a look at the strip chart told the tale… a tale of a perfectly recorded dip in the light exactly at the same time as the other telescope down the road!
The strip chart recorder used red ink. When it was illuminated by our red flashlight, the ink was impossible to see, because in that light everything is red…
(It was later determined… we had discovered a moon of Neptune.)
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