Relict radiation is electromagnetic cosmic radiation with a spectrum that is typical of an all-black body with a temperature equal to 2.725 degrees Kelvin. It appeared as early as the universe was born, although its temperature was much higher than it is now. This is due to the gradual decrease in the temperature of photons whose motion at the limit speed and there is relict radiation. It spreads relatively evenly, so the difference in temperature of the relict background in different parts of space, if and changes, then slightly. This means that it is possible to take as a basis the temperature of outer space, which is 2.725 degrees Kelvin.
However, the thermal radiation of stars must not be forgotten. Since vacuum is a wonderful thermal insulator, and space lacks atmosphere and grow.
So space is hot and cold at the same time depending on exactly what point it is measured at. Far from the stars, where almost no heat flux penetrates, it will be equal to about 2.725 degrees Kelvin, as relict radiation is uniformly spread throughout the Earth’s available for study astronomers part of the universe, but when approaching the star will gradually increase.