Science Facts

Why Is Space Cold? – Space Temperature Explanation

Space Temperature

Space is often referred to as a cold and dark place. But that is not always true. The temperature of space is dictated by where in space you are located. The way space gets hot and cold is very different than how we experience it on earth. When the Sun shines on the earth, it has to pass through our atmosphere. This makes the sun’s rays less intense and scatters the heat. It emits accordingly regulating the earth’s temperature, but the temperature concept is very different in space.

For example, there is technically no temperature in a vacuum-like space because of the lack of molecules to possess heat. However, this heat can be transferred by radiation, which is what stars emit. This radiation loses intensity over the distance that is why Pluto is much colder than Earth.

So if you were facing the Sun outside of Earth’s atmosphere, you would heat up quickly. The hotter you became, the more you would start to radiate heat, kind of like a space heater. And when you get hot enough, you will radiate enough heat to stop warming up. The shaded side of you would cool slowly because there is no air in space.

Why is space cold?

If observers were in a wholly shaded portion of space, they would not instantly freeze. It would take time for the heat to transfer away from their body because there is no air in space. And they would not come into contact with anything because there is technically no temperature coldness in space. It is comparable to emptiness. Some parts of space are extremely cold, but other parts are extremely hot. The coldness of space is determined by how close you are to a heat source.

Scientific explanation: Space is mostly full of empty or vacuum. It can’t move at all. It’s the very diffuse gases and grains that drift through the cosmos whose temperature scientists can measure. Sunlight and starlight might heat those atoms. They will cool back down by radiating heat. The heat will fly out into space with little chance of hitting and heating anything else in that vast emptiness.

On earth, we lose most of our heat by conduction. The body’s atoms bump into atoms of air or water, passing on that energy. Also, Nature wants to equilibrate where everything wiggles at the same speed. So if you’re warmer than your surroundings, you will lose heat.

  • There is no air or water in space, so the only way to lose heat is radiation. The atoms release energy directly into space. This is a slow process but continuous.

How cold is space? According to data from the cosmic background explorer satellite, the temperature of space is 2.725 Kelvin. It means 2.725 degrees above absolute zero. If atoms come to a complete stop, they are at absolute zero.

  • Space has an average temperature of 2.7 kelvin, about minus 455 degrees Fahrenheit.

This agrees with the temperature predicted to come from residual radiation after the big bang. And It is a refinement of ground-based measurements by Robert Wilson in 1964.

There are four states of matter: Solid, Liquid, Gas, and Plasma. But there’s a fifth ultracold state that is attracting a lot of attention: the Bose-Einstein Condensate. It is discovered during the late 20th century and the object of intense research ever since. This year, a condensate will make its way to the space station.

They suggested that when certain atoms are cooled to temperatures near zero, they lose their identities and crowd into a single quantum state. To get these atoms super cold, scientists use lasers. Lasers can be tuned so that atoms preferentially absorb photons when they move towards the laser.

Absorbing these laser photons slows down and cools the atoms. Inside a vacuum chamber, an array of laser beams cool a few atoms trapped within a magnetic field to just fractions of a degree above absolute zero.

Just like Einstein predicted when the temperatures get this low, regular physics seems to break down. This new matter forms into something called a superfluid. Superfluids are fluids that have zero viscosity. It means they flow without any friction or resistance. Not only that, but a BEC can behave much like a light wave.

A BEC can overlap and interfere with itself to spontaneously develop a rippled, wavy distribution of atoms. Such wave-like effects are rare among forms of matter. After they release the atoms from their magnetic traps and gravity brings them crashing to the bottom of their vacuum chamber. Scientists want to send BECs to space, where weightlessness gives them more time to perform experiments.

On Earth, the best way to mimic space’s weightlessness is by performing experiments during free fall. Some researchers aim to create BEC bubbles, a condensate that wouldn’t be possible back on Earth due to gravity. Other scientists are looking into cooling, not just atoms but individual molecules.

While the space station is better than Earth for maintaining BECs, vibrations from the machinery onboard keep it from being the perfect test bench. In the future, space-based experiments may be able to perform atom interferometry on the BECs.

More Articles:


Chuss, David T., Cosmic Background Explorer, NASA Goddard Space Flight Center.
Gupta, Anjali; Galeazzi, M.; Ursino, E. (May 2010), “Detection and Characterization of the Warm-Hot Intergalactic Medium,” Bulletin of the American Astronomical Society.

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