Well, there is snow on the ground and the daytime temperatures will be hovering around freezing now. Night-time temperatures will be well below freezing, so winter is here.
Here are some observing survival rules I have learned, observing from Michigan in temperatures down to –40C.
- Wear warm boots. When I meet people new to astronomy, they always want to know what the best telescope is and what accessories to buy. I always tell them, "the most important piece of equipment you will ever buy is warm boots". When it is clear, it is cold. If your feet are cold, you are miserable. If you are miserable, you are done.
- Wear a hat. Most of the heat in your body escapes through the top of your head like a chimney. Cover your head and retain body heat.
- Keep your hands warm. Mittens are better than gloves, but they are awkward to use when dealing with focuser knobs, charts, pens, pencils, etc. If you insist on wearing gloves, keep your hands in your pockets as much as you can and out of the wind. If your fingers begin to hurt from the cold, go inside or get in your car and warm them up thoroughly. Frostbite can be very painful.
- Get out of the wind. Most of the time it’s not the air temperature that gets you, it’s the wind-chill. Put a building or a hedge or an observatory between you and the wind and you will be able to endure the cold for twice as long. The added bonus of not having the telescope shake will save you time in making estimates.
- Don’t breathe on optics. Breathing on cold glass means instant frost. If you wear a scarf over your face, be sure not to let the warm air you exhale spill out over the top of the scarf and down onto the eyepiece. Set up your finder so you are not breathing on the eyepiece when looking through the finder. On very cold nights I usually have a large patch of frost to scrape off the back of the mirror cell of my SCT, caused by my breathing on the cell while looking through the finder.
- If you have dew heaters, use them right from the start of your session. They are much better at preventing frosted corrector plates, secondaries, eyepieces and finders than they are at removing frost. A heated box or holder for eyepieces can be a great benefit. If you only switch between a few, keep them in your pockets to stay warm.
- Keep your pen warm or the ink will freeze. I keep mine tucked behind my ear to keep it warm. I have one of those "astronaut pens". Even that froze at 40 below.
- Use a plastic flashlight. If you are like most of my friends who read charts and log observations by flashlight, you put the flashlight in your mouth to write. A very cold metal flashlight can be hard to remove from your lip without losing a bit of flesh. I suppose rule 8A would be, "don’t lick the telescope!"
- Take breaks every hour or half hour, depending on the weather, and go warm up. Keep an extra pair of dry socks warming on the dash of your car, or go in and throw a pair in the dryer for a few minutes. It’s amazing how a nice toasty pair of socks can change your attitude!
- Be aware of battery life in cold temperatures. The batteries in your flashlight, telescope, camera, dew heaters, etc., will perform poorly in cold temperatures. Keep warm extras handy.
- Keep your own personal battery charged. Plenty of rest, a good meal, snacks and hot coffee go a long way towards warding off the inevitable freeze. The search for a thermos that would keep coffee hot in sub-zero temperatures was my ‘Holy Grail’ for a long time. I finally found one at a camping supply store and it makes all the difference to me.
- Know your limits. You have to be realistic about how much cold, discomfort or pain you can endure in order to get those last few observations. Don’t wait until it’s too late and then decide to tear down and pack up. That’s when you will meet Mr. Frostbite.
With a little planning and common sense you can take advantage of those long, clear, cold winter nights. Orion, Gemini and Auriga are calling. Just be careful out there.