Orwell Astronomical Society (Ipswich)

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Cold-Weather Observing Wear

After a succession of cloudy, wet, days and nights, suddenly there's a break in the weather and the clouds drift away to reveal a perfect star-spangled night. You drag the telescope out of the cupboard, blow off the dust and wipe away the cobwebs. Then you step outside into that perfect night, only to be hit by a wall of ice-cold air. It's cold enough to freeze your finder off its mounting and you realise that you have only five minutes to observe before your enthusiasm expires from hypothermia! So, what do you do? You could: stick to solar observing; wait for balmy summer evenings; or get a CCD camera and rig it up so that you can work from the comfort of a fireside chair. Well, whereas solar, CCD and summer observing are enjoyable there is no reason why you should miss out on observing the best of the winter sky. By selecting the right clothing you can observe for as long as you like in comfort, even when the temperature dips far below freezing point.

When, in the late 18th Century, William1 and Caroline2 Herschel observed, they rubbed raw onion on their skins to reduce the biting cold in conditions which froze the ink in Caroline's inkwell as she wrote the observing log. Even if you can tolerate cold like such heroic observers of the past, if you dress sensibly to preserve your body heat you'll be more productive for longer and less prone to error if you are doing serious work and enjoy your observing more if you are doing it for fun.

The requirements for cold weather clothing for astronomy are usually different and generally technically easier than for many other outdoor pursuits. If you are observing from your back garden or after driving to an observing site you don't need to consider the need to wick perspiration or vary the amount of insulation as you would when hiking, for example. However, some of the clothing used for rambling, sailing, skiing, and other outdoor sports can also be used when observing. Clothing you already possess for everyday use plus one or two other items may be all that you need.

What you need to wear will depend markedly on the conditions in which you wish to observe and the local circumstances. For example, an observatory will provide protection from wind chill, though it should ideally be at the ambient temperature in order to avoid rising currents of hot air which will adversely effect seeing conditions. Your clothing requirements will also depend on your sensitivity to the cold.

Typically, almost half the body heat lost in cold conditions escapes from the head. Perhaps, for people engaged in astronomical observing, the proportion lost from the head may be even greater than average since the observer usually does not exert himself much except in thinking about the subject of observation, perhaps increasing the flow of blood in the brain! Having good insulation for the head and upper body will be all you need to keep comfortably warm in most conditions. If you keep the head and torso warm, your body will not try to conserve heat by constricting the blood flow to your extremities, and your hands and feet will not become unduly cold.

In keeping the upper body warm, lots of layers help trap air (which is the key insulating material) and are generally more effective than a smaller number of thicker items. Synthetic materials (e.g. polyester) are generally warmer than cotton. Wool also provides good insulation properties. Garments should be reasonably snug but not such an excessively tight fit that they restrict circulation or reduce the amount of trapped air. A good insulating coat, preferably with a hood, finishes off the basic equipment for the upper body. If you are in an unsheltered position, the top layer should be windproof or at the very least wind resistant.

The next most important thing is to reduce heat loss from your feet. Standing on a heat-conducting surface will accelerate heat lost in this way. A wooden floor will go a long way towards maintaining warm feet. Footwear should have soles which do not conduct heat readily but which do provide some insulation for the uppers. Of course, thick socks help too.

Under all but the coldest conditions most people will find that they can keep their hands uncovered for handling telescopes and cameras etc. if their head and body are very well insulated. However, when the air is bitingly cold, gloves will improve comfort. People who observe in extreme conditions, in the UK or abroad, might also want to consider a face mask. Even in slightly higher temperatures a scarf to wrap round your neck or face may be useful.

Recommendations for key areas of the body are as follows.

Head: A fleece, Thinsulate or woollen hat will significantly reduce heat loss and is arguably the most important single item even inside an unheated observatory. A balaclava or a hat with side flaps protects against chilly ears. An inherently windproof hat or the addition of a windproof layer is important if you aren't sheltered from the wind. I usually pull the hood of my coat over the top of a fleece hat for maximum insulation.

Body: For cold conditions start with a long sleeved thermal top. I prefer not to have wool in the base layer as I find even soft wool slightly irritating; polyester is more comfortable. The middle layers could include one or two items such as thick shirts or sweatshirts. Sweatshirts and thick shirts are often 100% cotton but it is possible to find examples which are 100% synthetic or have a high proportion of synthetic material. A chunky wool jumper makes an efficient next layer though you may have to look around in outdoor and camping shops or yacht chandlers to find a good one. The next layer should be a warm well-insulated coat which is wind resistant (a wind resistant layer can reduce heat loss in calm conditions and windy conditions). In moderately cold conditions I find the fleece jacket and waterproof shell that I use for hill walking provide sufficient insulation, but in colder conditions the addition of a quilted body warmer or a switch to a more insulating coat is necessary. (A fleece could even be next-to-last-layer with a coat on top). A lined parka or quilted walking coat or ski jacket are all possibilities for the outer layer. I have seen a range of coats used by observers work well, ranging from an army surplus thermal lined parka costing £15 to a down-filled mountaineer's jacket costing around £2503.

Legs: A pair of long trousers is generally a good idea in cold weather! A pair of full-length thermals, just like the thermal top, under ordinary trousers is often all that you need. Jeans are not efficient at retaining heat and are not windproof, so go for ordinary trousers or specially designed thermal trousers instead. In outdoor pursuits shops you can find trousers designed for hiking which are made from a thick insulating material and others which have a thermal lining. Optionally, a pair of long-john style salopettes (padded trousers) on top of the other two layers can provide effective protection against very cold conditions.

Hands: You could use woollen or padded (e.g. Thinsulate) gloves which can be easily removed when adjusting the telescope. Alternatively, thin liner gloves will provide some protection whilst allowing you to operate fiddly equipment without removing them. They are designed to be worn under thicker gloves for conditions of extreme cold when mountaineering but, for cold-weather observing in Southern England, they are usually sufficient on their own. Fingerless gloves are an alternative and may be better if your optical equipment is particularly fiddly. For very cold conditions you could try liner gloves with fingerless gloves on top. I like to use a pair of thin liner gloves and also have a pair of Thinsulate padded gloves just in case. Often I find that even in quite cold conditions the gloves are not critical if the rest of ones clothing is effective at retaining heat.

Feet: Ordinary shoes often conduct too much heat away from the feet when standing on cold ground. Trainers usually have insufficient insulation in their uppers and are not generally recommended, but I should mention that one member of OASI finds his trainers (with standard department store thermal socks) the ideal footwear for observing because the insulating properties of the soles keep his feet warm even when standing on a cold surface. Ordinary shoes, particularly those with leather soles, are not very effective at keeping feet warm. Walking boots, ski boots or a pair of insulated moon boots will certainly help4. Sometimes standard ankle length thermal socks are all you need but in colder conditions or if you are prone to cold feet, then long warm socks - woollen walking socks or skiing socks - on top of either ordinary socks or thin thermal liner socks are needed. My preference for very cold conditions is a pair of thin thermal liner socks with knee-length mountaineering socks (designed to prevent frostbite when trekking across the poles and on mountain tops) worn with a pair of walking boots.


To keep warm under adverse conditions, concentrate on the head, torso and feet. Use multiple layers of clothing made from synthetic materials and wool. Cotton is not good for insulation. Clothes should be snug (but not too tight) in order to trap lots of air which is the key to keeping warm. Avoid jeans and use standard trousers made from synthetic or wool material. A pair of thermals underneath trousers or salopettes on top are good ways to improve your insulation. Gloves can add to your comfort.



William Herschel is famous for the discovery, from his back garden in Bath, in 1781, of Uranus, the first planet to be discovered beyond those known since ancient times. He also mapped the distribution of the stars in three dimensions to produce the first model of what we now know as the galaxy, and discovered infra-red light.


Caroline Hershel holds, to this day, holds the record for the largest number of comet discoveries by direct observation by a UK observer.


A duvet jacket is generally unnecessary for observing since you can use bulkier coats and more layers which are heavier but less expensive. As well as those whose other interests warrant buying a duvet jacket, amateur astronomers who go on observing expeditions abroad in very cold conditions (e.g. observing aurora in Alaska) may find it a justifiable purchase. Having bought such a jacket one OASI member finds the jacket is all that's needed on top of jeans and T-shirt to go out observing in the back garden on cold evenings!


I tried Wellington boots (with walking socks underneath) one evening but I found my feet got very cold. I have seen insulated Wellingtons which might be better.

Pete Richards