Cosmic microwave background
The cosmic microwave background is faint thermal radiation filling the universe, left over from the early stages after the Big Bang.
How big is it?
2.725 K
Also -454.8 °F
Temperature · approximate
A little perspective
Cosmic microwave background is 1.495 K cooler than Boiling helium.
Boiling helium: Boiling helium is helium in its liquid state at its normal boiling point under standard atmospheric pressure.
Measurements, assumptions & sources +
Cosmic microwave background
The temperature of the nearly blackbody relic radiation. It is not the temperature of every object in space.
The marked temperature is calibrated. Unmeasured illustration details are representative.
Boiling helium
Approximate normal boiling point of helium at one atmosphere.
NIST Chemistry WebBook — Helium phase data
The marked temperature is calibrated. Unmeasured illustration details are representative.
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Why this measurement?
Why we use 2.725 K
For comparison, this page uses temperature. This is labelled approximate; the central value is useful for comparison, while real values or measurement solutions can vary.
The temperature of the nearly blackbody relic radiation. It is not the temperature of every object in space.
The identifying illustration and the numerical comparison remain separate. How calibrated comparisons work →
Recorded properties
Cosmic microwave background dimensions and measurements
| Property | Selected value | Recorded range | Basis |
|---|---|---|---|
| 2.725 K | Not recorded | approximate |
Around this scale
Go smaller. Go bigger.
These links use compatible temperature records, ordered around the selected value.
Nearest lower value · TemperatureAbsolute zero0 KAbsolute zero is the lowest temperature permitted by thermodynamics, where a system has the least thermal energy available to it.Around the same scale · TemperatureSuperfluid helium lambda point2.17 KThe superfluid helium lambda point is the temperature at which helium-4 transitions from a normal liquid to a superfluid state.Nearest higher value · TemperatureBoiling helium4.22 KBoiling helium is helium in its liquid state at its normal boiling point under standard atmospheric pressure.Sources and method
Want to check the number?
The source records and measurement method remain available for inspection.
- NASA — COBE science resultsCosmic microwave background blackbody temperature about 2.725 K; this is radiation temperature, not the temperature of every object in space.
More ways to see it
Curated comparisons
There’s always another scale
Follow your curiosity.
TemperatureAbsolute zero0 KAbsolute zero is the lowest temperature permitted by thermodynamics, where a system has the least thermal energy available to it.TemperatureRoom temperature20 °CRoom temperature describes indoor air conditions generally considered comfortable for people and suitable for ordinary activities.
SpaceSun1,391,000 kmThe Sun is the star at the centre of the Solar System.
Fundamental physicsPlanck temperature1.417 × 10³² KThe Planck temperature is a theoretical temperature scale at which quantum gravitational effects are expected to become important.TemperatureBoiling helium4.22 KBoiling helium is helium in its liquid state at its normal boiling point under standard atmospheric pressure.TemperatureUltracold atom cloud1 × 10⁻⁷ KAn ultracold atom cloud is a collection of atoms cooled to temperatures near absolute zero, used in advanced physics experiments.TemperatureBoiling nitrogen77.36 KBoiling nitrogen is nitrogen gas produced when liquid nitrogen is heated at normal atmospheric pressure.TemperatureSuperfluid helium lambda point2.17 KThe superfluid helium lambda point is the temperature at which helium-4 transitions from a normal liquid to a superfluid state.