Another way of measuring temperature in space is to look at the background radiation emitted by the whole universe. This is known as cosmic background radiation. It was discovered by Penzias and Wilson in 1965.
Since then, scientists have been trying to work out how old the universe is. One way of doing this is to calculate how much radiation has been coming from the universe since its birth 13 billion years ago in the Big Bang. By comparing this with the current level of radiation, we can work out how long it has taken for the universe to reach its present state.
The most recent measurements show that the universe is just over 14 billion years old. We now know that the universe started off extremely hot. But after about 380 000 years, the temperature dropped dramatically. CMB is currently at a temperature of 2.7 K (0.000273 degrees kelvin) which is minus 459.67 degrees Fahrenheit, or minus 273.15 degrees Celsius!