It depends on which part of the space we are talking about. In general, it works like this: the closer to the stars, the higher the temperature. Another factor that weighs is the presence of matter: heat can be retained by it. As space becomes empty, temperature drops. In a vacuum (absence of matter), the temperature drops to 2.7 Kelvin or -270.45 Celsius. Only a few degrees above absolute zero (-273.15 °C).
There is no place colder than space. It has a lot of empty regions distant from heated bodies. The lowest temperature ever recorded on Earth was -89.2 ºC, in Antarctica. In interstellar space, where there is no absolute void (there are gases and dust grains), the temperature varies.
At the Earth’s thermosphere, where the atmosphere turns into space, the exact temperature can also vary substantially. However, the average temperature above 300 km is about 427 degrees Celsius at solar minimum and 927 degrees Celsius at solar maximum. But this does not mean that the space above the atmosphere is at this temperature. In fact, it is very cold. Only a body in this region that is illuminated by the sun can reach this temperature. In the dark areas of space, temperatures would drop a lot.
On the Moon, which has no atmosphere, temperatures vary a lot. When sunlight reaches the moon’s surface, the temperature can reach 127 degrees Celsius. However, when the sun goes down, temperatures can drop to – 173 degrees Celsius.
The distance from the stars and the presence of matter influence the average temperature of the planets.
Table of contents – Why is space so cold?
Temperature of the Sun
The temperature of the Sun’s surface that is visible from Earth, the photosphere is 5500 ºC. Some stars can pass 50000 ºC. Inside the Sun, however, it gets hot: the heat reaches 15 million degrees Celsius!
Earth is kept warm due to its atmosphere and the five layers it contains. Solar radiation and its interaction with the earth’s soil define the heat that it generates here. About 47% of the heat emitted by the Sun is absorbed by the Earth. The other solid planets of our solar system are Mercury, Venus and Mars.
There is little matter in the space between the planets or between the stars, which is composed mainly of gases and space dust. Air is very rare in space. Temperatures can reach about 2.7 Kelvin (-270 degrees Celsius) in the space between the Earth and the Moon. For example, the sensation we would have there (without special clothing) would be of severe cold. The reason for that is the small amount of molecules in space. It is simply not enough to transfer a significant amount of heat to our skin or to the spaceships that travel in space.
Without a solid surface, the gaseous material simply becomes denser depending on the depth and can reach a liquid state. Jupiter, Saturn, Uranus and Neptune are composed mainly of hydrogen and helium. Besides not having solid matter, these planets are more distant from the Sun, which makes heat a rare thing there. They are hot only in the deepest layers.
Formed by a cloud of gas and dust, the Boomerang nebula registers a temperature of about 1 Kelvin (-272 ºC). Only 1 degree Celsius above absolute zero. It seems to be the coldest place in the Universe, but the mystery has not yet been fully unraveled. The nebula lies in Centaur, one of the constellations of the Milky Way, in the southeastern celestial hemisphere, 5,000 light-years from Earth.