Sun
Star
Facts
- Mean diameter
- 1,391,400 km
- Mass
- more than 330,000 times Earth
- Age
- about 4.6 billion years
- Surface temperature
- 5772 K (photosphere)
- Core temperature
- about 15.7 million K
- Rotation
- 25 days at the equator, 36 at the poles
The Sun is the star at the centre of the Solar System: a glowing sphere of hydrogen and helium, a yellow dwarf of spectral class G2 V that on its own holds 99.8% of the Solar System's mass. It would take about 1.3 million Earths to fill its volume.
In the core, about 138,000 km thick, the temperature exceeds 15 million °C, and the energy produced there takes about 170,000 years to reach the top of the convective zone. The photosphere, the surface we see, is about 400 km thick and reaches about 5500 °C; the corona, the outer atmosphere, is far hotter: up to about 2 million °C.
Material leaving the corona at supersonic speed becomes the solar wind, which inflates a magnetic bubble around the Sun, the heliosphere, reaching far beyond the orbits of the planets. Roughly every 11 years the Sun's magnetic poles flip: this is the solar cycle, and cycle 25 began in December 2019.
Together with the whole Solar System it travels around the centre of the Milky Way at about 720,000 km/h, or 200 km every second. Even at that speed it takes about 230 million years to complete one lap, a journey of about 150,000 light-years.
It is a little under halfway through its life: in about 5 billion years it will swell into a red giant that could engulf Mercury, Venus and perhaps Earth, before ending up as a white dwarf.