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Cold-weather observing

Use these precautions to make your winter observing safe and productive.
Low temperatures are hard on equipment, vehicles, and people. Cameras malfunction, batteries go dead, and there's a risk of hypothermia and frostbite. Still, the prospect of a clear, winter night is tough to resist. For low-temperature observing, the law is simply, "Preparation is everything."

Being prepared doesn't mean just owning the right equipment. It means having what you need at hand for that which you did not expect. So my first tip is to overpack. In the most improbable situation, having a certain item along could literally be the difference between life and death.
Cold weather wear
The problem of keeping warm, like any other physical problem, can be attacked by the scientific method. This was done by the U.S. armed forces during World War II and the Korean War. The key result of the studies was that the only effective insulator is "dead air space," tiny pockets of air held immobile by fibers of insulation. Thus, only the thickness of the insulation matters: the thicker the better.
Astronomy
The most important body parts to keep warm are the head and feet. Most heat loss during cold evenings is through the top of the head. And nothing will chill you faster than heat seeping into the ground through thin shoes. Choose headgear that consists of a pullover head-cover made of soft fleece. Over this, wear a wide-brimmed hat.

Purchase the warmest boots that allow you to drive a vehicle. I usually change into and out of my cold-weather boots at the observing site, but you never can tell what might happen. You may be required to drive to a new location without the time to change footwear. Choose boots that are comfortable, not very heavy, and have a thick, insulated lining in the sole to prevent heat transfer downward.

Bring hand warmers, and bring extras. Warmers are superb when working but notorious for not lasting the full time specified on the package. Keep active warmers in your side pockets. Slip them in and out of your gloves or mittens for a quick warm-up.

Finally, dress in layers. I generally wear fleece long underwear and thick pants. My upper body is covered with a T-shirt, a thin, long-sleeved, flannel shirt, a fleece pullover, and a down jacket. My wife, who is affected by the cold to a much greater extent than I am, wears a ski-rescue suit as her outer layer. When fully zipped with the hood up and boots and gloves in place, the wind has few places to chill her delicate frame.
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