And why not? Cold weather kills about 3 million people a year world-wide, about 150,000 people alone in the U.S. and 50,000 in Britain, despite them being a 1st world countries. Flu outbreaks, all of it is worse. I've observed for 3 hours in -20 deg temps sometimes, but I can't say it's a good idea. Problem is, skies are better in winter owing to less water vapour being in the air. Nighttime lasts twice as long too. Observing from a backyard is easy, but often dark-sky sites are hampered (or closed) by snow in northern or mid-western areas.