As an amateur photographer I'm familiar with the idea of light having a colour temperature and having to adjust a camera for white balance e.g. early morning light is much warmer than midday. I've read in books on photography that light before dawn is always colder than the light after sunset.  I would have expected it to be the same.  Why should the direction of the light affect its temperature? Is this just a UK phenomenon or is it worldwide ?

While visiting Magna in Rotherham recently, my son asked me a question I couldn't answer. What is the bucket that pours the molten steel made of? And how is it made? It must be made of an alloy with a higher melting point than steel, so how is it made? And how is the machinery used to make that made? And how is the machinery used to make that machinery made? You could go on for some time with this chain of production, but it all comes down to how do you make machinery for something that has a massively high melting point? What is it made of and how is it made?

Thanks for your help,

Peter and Alfie Finan, Haworth, West Yorkshire

I spent time in the Scottish hills last winter and on a couple of occasions I had cause to clean my glasses in a stream that originated from melting snow, effectively at 0 °C. The water cooled the glass and its metal frame to such an extent that both lenses fell out.

But how could this happen when, if I remember my A-level physics correctly, metal should contract more than optical glass because of a higher coefficient of expansion?

Obviously this has never happened when I've been walking around under normal conditions.

Andy Douse, Drumnadrochit, Invernesshire, UK

We received some very entertaining answers to this question, but we haven't really nailed it yet. Several people called for more experimentation or wanted to know the coefficients of expansion for optical plastics so that they could be compared with those for metals - Ed