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What's the Temperature of Outer Space?

A close-up of one active region on the sun, seen in profile in extreme ultraviolet light, produced an interesting display of dynamic and frenetic sputtering over three days (Aug. 28-30, 2011).
A close-up of one active region on the sun, seen in profile in extreme ultraviolet light, produced an interesting display of dynamic and frenetic sputtering over three days (Aug. 28-30, 2011). (Image credit: NASA/SDO)

Some parts of space are hot! Gas between stars, as well as the solar wind, both seem to be what we call "empty space," yet they can be more than a thousand degrees, even millions of degrees.

However, there's also what’s known as the cosmic background temperature, which is minus 455 degrees Fahrenheit. So what would a thermometer in space reveal? Somewhere between those extremes — depending on whether it's in the sun or the shade.

Here's what’s going on: Most of the gas in space is too thin to warm anything up. Essentially, there are not enough gas particles to "bump" into and transfer heat to an object. So if you were in space, but shielded from the sun, you would radiate away nearly all your heat pretty quickly and cool to the cosmic background temperature. Step (or float) into the sun, and you’d be warmed. Either way you'd need lots of protection!

At the Earth's distance from the sun, a space thermometer with roughly half its surface is absorbing sunlightwould register 45 degrees Fahrenheit.

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Space.com Staff

Space.com is the premier source of space exploration, innovation and astronomy news, chronicling (and celebrating) humanity's ongoing expansion across the final frontier. Originally founded in 1999, Space.com is, and always has been, the passion of writers and editors who are space fans and also trained journalists. Our current news team consists of Editor-in-Chief Tariq Malik; Editor Hanneke Weitering, Senior Space Writer Mike Wall; Senior Writer Meghan Bartels; Senior Writer Chelsea Gohd, Senior Writer Tereza Pultarova and Staff Writer Alexander Cox. Senior Producer Steve Spaleta oversees our space videos, with Kim Hickock as our Reference Editor and Diana Whitcroft as our Social Media Editor.