Just like with everything in our surroundings, it is necessary to determine under what conditions we want to measure the temperature in. For example, water can be at 4 °C in the refrigerator, 95 °C in an electric kettle, and around 300 °C in a power plant (typically nuclear). So electrons or protons can have different temperatures in different places, with the range of values being much greater than the stated values for water.

Before I present the various values of electron temperatures, I need to provide some information about temperature. Temperature (simplified) shows us the (internal) energy of a given body, as it is related to the speed of particle movement. The faster the particles in a substance (atoms, molecules) move, the higher the temperature we will measure. Temperature is therefore a kind of indicator of the energy present in a given body. If we supply energy to a body (typically by adding heat), its energy will increase (energy cannot be lost), and we observe this increase in energy as an increase in temperature. The amount by which the temperature increases depends on the number of particles in the body (the more there are, the more heat we need to add to the body for it to warm up). This explains why the Earth’s atmosphere at an altitude of over 100 km has a temperature of over 100 °C — the gas molecules themselves move very quickly (and therefore have a high temperature), but there are very few of them to burn the objects that are at this altitude.

Therefore, electrons can have a high temperature, but that doesn’t mean we will feel this temperature significantly — for example, an electron in old (CRT) televisions had a temperature of over 100,000,000 °C! We certainly did not observe that the televisions immediately caught fire upon being turned on.

We can easily determine the temperature of electrons using the Boltzmann relation: E=3/2*k*T, where k is the Boltzmann constant, T is the temperature in Kelvin, and E is the energy of the electron. It is easy to find out that in the atomic shell, electrons have the temperature of its surroundings; on the Sun, the temperature of electrons is in the range of hundreds of millions °C, and in space, electrons have a temperature on the order of hundreds of thousands °C.