clusters, glowing nebulae and other stargazer’s delights. It was

clusters, glowing nebulae and other stargazer’s delights. It was used as an illustration in an astronomy textbook.

This historically famous comet signaled the invasion of England by William the Conqueror when it came in 1066 and the defeat of Carthage by Rome in 241 B.C. I first read about comet Halley in grade school, and I had been waiting for its return for 50 years. It won’t be seen again until the year 2062.

But our crystal-clear skies have one disadvantage. The air is more transparent than a pane of glass, and when the wind dies away there is next to nothing between Rappahannock County and the cold depths of space. All through the night the temperature falls. Astronomers call it “Radiation Cooling.” On some cloudless, wind-free nights I have measured a temperature drop of 40 degrees.

In the summer that is welcomed, but in the winter it is not. No other place in the United States seems to match this — except perhaps Casper, Wyo.

I should have known better when I was photographing Halley’s comet. The camera felt cold through my gloves. The air was still, and I didn’t notice the white frost collecting on the stubble of the hay field. It was one of those 40-degree drops, from a warm 55 down to 15 degrees.

The next morning I woke up with mild lumbago — not a bad case, but enough of a backache to make me walk around slowly, with a noticeable limp.

A friend saw me at the Farmers’ Cooperative, and when he realized I w'asn’t bending down to pull something off the shelf, he asked me how I got that way.

Now a backache isn’t much fun, and somehow I didn’t feel like talking very much.

“Got it from Halley’s comet,” I said.

He didn’t seem to understand what I was saying.

“Radiation cooling,” I explained.

That ended the conversation.

Dr. Gerald Hawkins is an internationally-acclaimed astronomer and authcn', whose books include Stonehenge Decoded and Beyond Stonehenge.