Mercury madness

I have asked many people this, including my parents and science teacher, but they don’t know the answer. If a thermometer was in space, what would it read? Thanks to those who pointed  out the complicating nature of  the title. A thermometer using mercury would be useless in  space for the reason below – Ed ■  A mercury thermometer would stop working at 234 kelvin (-39 °C) – the temperature at which mercury freezes – but there are types of thermometer that would work. If the thermometer was in Earth’s shadow and there was no moonlight, then it would read about 3 K. This would be because of cosmic microwave background radiation at 2.7 K and some infrared radiation from the night side of Earth. If it was in direct sunlight, the temperature would be about 500 K (230 ˚C), which  is why some spacecraft such as  the Apollo lunar modules were wrapped in gold foil to stop them overheating.  So the short answer is it would record anything from 2.7 K to millions of degrees, depending on where it is in space. Andy Biddulph Burton upon Trent, Staffordshire, UK ■  In the vacuum of space,  there are virtually no particles  to conduct or convect heat, so  a thermometer would not be affected by these processes. However, it would still be affected by radiation from stars and cosmic microwave background radiation. Also, the thermometer will radiate away any residual heat until it reaches equilibrium with its surroundings – in this case  the same temperature as space. Because collisions with photons emitted from stars are rare, the thermometer will essentially measure only the temperature of the cosmic microwave background radiation, so it would read about 3 kelvin (or -270 °C). Lewis O’Shaughnessy Salisbury, Wiltshire, UK