How hot is the Sun?
The Sun's visible surface is about 5,500°C (10,000°F). Its core reaches about 15 million degrees Celsius, and its outer atmosphere, the corona, is over a million degrees.
The surface we see, called the photosphere, is cooler than most of the Sun. Darker patches called sunspots are cooler still, at about 3,500 to 4,500°C, and look dark only by comparison with the bright areas around them.
Deep in the core, the temperature and pressure are high enough for hydrogen to fuse into helium. That process powers the Sun and all life on Earth.
The corona puzzle
Strangely, the corona, the Sun's thin outer atmosphere, is hundreds of times hotter than the surface below it. Scientists think magnetic waves and small explosions carry energy upward, but the details are still being studied. NASA's Parker Solar Probe has flown through the corona to investigate.
The Sun's heat travels to Earth as light and other radiation across about 150 million kilometers of space. Only a tiny fraction reaches our planet, but it is enough to drive the weather, the water cycle and photosynthesis in plants.
Did You Know?
The Parker Solar Probe became the fastest human-made object, passing about 690,000 km/h during its closest approaches to the Sun.