Fun Facts
Absolute zero is easy to picture: so cold that nothing moves. The Sun is the opposite problem. It's so hot the number stops meaning anything. Here's the whole range, from 0 K to 1.4 × 10³² K, on one slider.
This scale is logarithmic: every notch is ten times hotter than the one before it. That's the only way to fit a 38-trillionths-of-a-degree lab experiment and the first instant of the Big Bang on the same screen. Drag the slider, or tap any entry in the list below to jump to it.
Temperature isn't really a "thing" on its own. It's a measure of how fast atoms and molecules are jiggling around. The nitrogen molecules in the room you're sitting in are zipping around at about 470 meters per second, faster than a rifle bullet, bouncing off each other billions of times a second. Cool the air down and they slow. Keep cooling and eventually you reach 0 K (−273.15 °C, −459.67 °F), the point where there's no motion left to take away.
Two catches make absolute zero stranger than "everything stops":
Space itself is not at absolute zero. Empty space everywhere is bathed in the afterglow of the Big Bang, the cosmic microwave background, which sets a floor of 2.725 K. The one natural place known to be colder is the Boomerang Nebula, about 1 K, where gas blasting away from a dying star expands so fast it refrigerates itself below the background.
The Sun's visible surface is about 5,772 K (roughly 5,500 °C or 9,900 °F). That's already beyond the melting point of every material humans have ever made; the record-holding ceramics give up at around 4,000 °C. And the surface is the cool part.
Numbers like "15.7 million" slide right off the brain, so try this instead. Put absolute zero at one end of a ruler and room temperature 1 inch away. On that same ruler:
| Temperature | Distance on the ruler |
|---|---|
| Room temperature (293 K) | 1 inch |
| Water boils (373 K) | 1.3 inches |
| Sun's surface (5,772 K) | about 20 inches |
| Sun's core (15.7 million K) | about 0.85 miles |
| Supernova core (~100 billion K) | about 8,700 km, most of the way through Earth |
| LHC quark-gluon plasma (5.5 trillion K) | about 477,000 km, past the Moon |
| Planck temperature (1.4 × 10³² K) | about 1.3 trillion light-years, 14× wider than the observable universe |
Everything that has ever happened in your life, from a winter morning to a pot of boiling pasta, happens inside the first inch and a half.
There's one more twist. The Sun's thin outer atmosphere, the corona, is somewhere between 1 and 3 million K, hundreds of times hotter than the surface underneath it. Moving away from a campfire normally makes you colder, not hotter, and exactly why the corona runs so hot is still one of the big open questions in solar physics. The leading suspects are magnetic waves and countless tiny magnetic "snaps" (nanoflares) dumping energy upward.
The single biggest temperature swing that has ever happened is the one we're all living inside. The universe started unimaginably hot and has been cooling ever since as space expands and stretches every wave of light in it. Slide from the first instant after the Big Bang to today.
Notice how much of the drama is crammed into the first few minutes. By the time the universe was 3 minutes old, it had already cooled from the Planck temperature to about a billion kelvin, cool enough for the first atomic nuclei to hold together. It then took another 380,000 years to cool to about 3,000 K, cool enough for electrons to settle onto those nuclei and let light travel freely. That released light is the same glow we still see today as the 2.725 K microwave background, stretched out by 13.8 billion years of expansion.
Simplified: between marked eras the curve is a smooth estimate, and it skips the brief supercooling during cosmic inflation. Temperatures before about a trillionth of a second are theoretical extrapolations, not measurements.