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• Astronomy
• Temperature
• NASA

# What is the temperature in space?

###### Wiki User

The temperature in space is close to "absolute zero" because any object there will radiate heat until it cools to that point. This is for objects not exposed to direct sunlight. In Earth orbit, the temperature of objects in sunlight can rise to 120Â°C/ 250Â°F. The actual temperature in space is about 3Â°K (-270Â°C or three degrees Celsius above Absolute Zero). There are still molecules in space, just very few of them, and this is their temperature.

Absolute zero is a theoretical temperature where the thermal kinetic energy of the molecules in a body goes to zero. This cannot be achieved through artificial or natural means, because there is no way to remove the last small amount of thermal energy. The coldest temperature in space is about 3Â°K above absolute zero. This is defined as the Cosmic Background (or Microwave Background) Radiation that was first detected by Penzias and Wilson using the Holmdel Horn Antenna in New Jersey, USA in 1965. This radiation quite literally is the echo of the Big Bang.

Assuming you're measuring the temperature of pure space, or an area in which there is no matter that could absorb the sun's radiation and thereby heat up, the temperature would be -459Â° Fahrenheit, -273Â° Celsius, or 0 on the Kelvin scale.

Cosmic Background RadiationThe temperature is not absolute zero because there is a pervasive background radiation, with an equivalent temperature of 2.7 K. Alternate view:This is an amateur opinion. When measuring, for example, the heat of a distant star, one is not measuring the heat of the intervening space, even though the radiation we are detecting passes through it. It is possible that the same thing can be argued for the background radiation. An analogy might be that if a photon of light reaches earth, it is because that photon was not absorbed by anything during its trip, not even the tiniest particle of matter. Clearly, photons that are absorbed along the way never reach us. It might even be possible in a weird quantum sense that the photon may just be a probability greater than 0 and less than 1 until and unless it is absorbed by something.

So it may be that completely empty space has no temperature at all (not even absolute zero), because there is nothing in it to either absorb or be void of heat. Empty space is not capable of absorbing or radiating heat. If a thermometer were placed in absolutely empty intergalactic space, it would probably eventually register the background radiation, but this would be because the thermometer itself has absorbed radiation that would otherwise not have been absorbed and that would have continued to propagate through space.

Here is another way to consider the same question. Say that a perfect or near perfect vacuum could be created here on earth, in a lab at ordinary room temperature. What would you claim to be the temperature of this vacuum, and what information would you use to support your claim? Temperature is a characteristic of matter, and not of vacuum.

Correction to the aboveThe question does not ask the temperature OF space, but rather IN space. Radiation from anything in space will cool it without any need for a conducting medium. The loss of heat will continue until the object reaches very nearly absolute zero. If an object receives sufficient radiation from the Sun, it will heat only the surface exposed to the Sun, and cool from the others. So spacecraft that are designed to reflect the Sun's heat will need another heat source to keep the interior warm. This varies from temp to temp. Usually it is 2-4 degrees kelvin. Sometimes hotter depending on where you are in space. Otherwise it is -400 degrees Fahrenheit. Pretty darn cold if you ask me. Don't go into the cold recesses of space without a space suite.
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