How hot or cold is that, on a cosmic scale?
Temperatures in the universe span from 2.7 kelvin to hundreds of millions. Human comfort occupies a very narrow band of it.
1.04 × Earth average
300 K is hotter than 5 of the 9 references on this page.
Reference figures are measurements and are rounded; the unit conversion behind them is exact.
| Reference | Size | Yours ÷ theirs | Note |
|---|---|---|---|
| Boomerang Nebula | 1 K | 300× | The coldest natural place known |
| cosmic microwave background | 2.73 K | 110× | |
| Pluto surface | 44 K | 6.82× | |
| Mars average | 210 K | 1.43× | |
| Earth average | 288 K | 1.04× | |
| Venus surface | 737 K | 0.407× | |
| Sun’s surface | 5,772 K | 1/19.2 | |
| lightning channel | 30,000 K | 1/100 | |
| Sun’s core | 15,700,000 K | 1/52,333 |
Worth knowing
- The Boomerang Nebula is 1 K — colder than the cosmic microwave background, because its own expansion is cooling it faster than the universe warms it.
- Venus is hotter than Mercury despite being twice as far from the Sun, entirely because of its atmosphere.
Frequently asked
What is the temperature of space?
Empty space sits at 2.725 K, the temperature of the cosmic microwave background. An object in sunlight will be far hotter, and one in shadow only slightly colder.
Why does space feel cold if there is nothing there?
Because you lose heat by radiation with nothing to gain it back from. There is no conduction or convection, so cooling is slow but relentless.