Saturday, January 7, 2012

Keeping Warm When Observing in Winter

Winter skies can be some of the best of the year. But it's hard to enjoy them if you're not safe and comfortable while observing. Cold air may being doing something wonderful for the skies above, but there are lowly land-level things to take into consideration.

Losing Sky to Gain Warmth
Where you observe can have a lot of effect on the conditions. Open areas far from buildings and trees are the best for views of the sky, but they are usually the coldest as well. Ground level temperatures at night are strongly affected by radiation of heat from the ground. When the area has a clear view of the sky, it radiates its daytime heat more readily into the sky, cooling more and faster than if it has partial cover.

If it's just plain too cold to enjoy the sky from a completely open area, observing the sky from one or more sites that have some partial cover can save the evening. It can be several degrees warmer in a location that has partial tree cover. Buildings keep the areas immediately next to them warmer as well. If you are viewing in a direction away from the building, any air currents caused by heat coming off the top if the building can be avoided.

By choosing partially covered locations well, you can move from place to place and be able to observe all or most of the sky without being quite so cold.

Cover the Cold Ground
Observing atop a non-porous ground cover helps significantly as well. A tarp or sheet of painter's plastic makes a good ground cover. Something else thrown on top of the ground cover will help keep the site even warmer. An old blanket, chunk of carpet, or some other form of insulating material on top of a ground cover will help make the observing site far more comfortable.

If there is any wind, some form of wind block will obviously be helpful to staying warmer. For foliage and sizable structures, you'll usually get the best protection on the downwind side of it. For smaller or erected wind breaks, the best protection may be on the downwind side but in many cases will be on the upwind side. In these instances a dead zone forms in the upwind area, whereas the downwind side may actually be colder due to air flow caused by the low pressure area formed on the downwind side. Be prepared to try both. This can also occur with some building layouts, but is more common with small wind screens, fences, and the like.

Slippery Slopes
Sloping ground can also be colder than flat areas. Convection along the sloping surface can make for a drifting draft that chills astronomers. At my prior home we lived on a slope just beneath a ridge line. Our weather was far colder than many other places at our elevation. We would have snow at times when the properties around us were clear. Our location gave us a great view of the sky, but it was colder.

In one corner of our property there was a dell with less of a view of the sky, but warmer air tended to pool there for some reason (I'd have expected it to be colder.) But I noticed that snow appeared there later than anywhere else nearby. Once snow got in there it stayed later than anywhere around because it received little sunlight. But at night, it was one of the warmest places to be, thanks to low airflow, partial tree cover, and a thick bed of leaves on the ground.

It's also important to be in a safe place to stand and move around a bit in the dark. Our present property has a steep section above a cut. It happens to give the best views to the north and east, but most of it isn't safe to traverse at night without light and extreme care. For this reason, I avoid it. Falls and injuries are a bad way to end an observing session. And it doesn't get you any warmer.

Warm Up Shack
Having a nearby location where you can take breaks from observing and warm up is a good idea. My number one observing location is at home, but I also travel to nearby locations that give a better view than my home. At the very least, I have my car as a place to go for breaks. I keep both a wool blanket or sleeping bag and a space blanket on hand. I run the engine for the heater while inside, and put a piece of cardboard on the dash to block the lights to preserve my night vision.

I keep some high calorie snacks in there, and a thermos of something warm to drink when I've though ahead that far (boy, I regret it when I don't!)

A car isn't the best warm-up shack, and a club site or other prepared observing location can have a dark warm-up room that allows you to duck in for a while to warm up, count your appendages, and generally decide whether to continue your time under the sky in warmth and comfort without having to wait half an hour for your night vision to fully return just because you wanted to get in out of the cold for a bit.

At home, I work with my family to choose a door I can go in and out of to a darkened area. That makes it easier for me to come in every so often without having my night vision ruined every time I do. Usually I keep my log and a red LED light there, I'll update my log while I'm warming up and possibly think of some more things I can look at if I go back out.

Having something to do when I first come in makes it easier for me to wait the time it takes to get warm enough to make a reasonable decision about whether I should go back out, and to keep me from rushing back out before I'm really completely warmed up. Not being able to feel your feet isn't a good sign, but it's one I've missed at times when I didn't make sure I got warmed up properly before going back out (fortunately the warming was enough that I did get sharp pains about ten minutes after going back out, rather than just numbness. That hint I did catch!)

Prepare Yourself

In the next article I'll discuss what you can do in the way of clothing and self-preparation to make winter observing more enjoyable.

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