The Sun

Key facts

Diameter

1,392,700 km109× Earth

Mass

1.989 × 10³⁰ kg≈ 333,000× Earth

Surface gravity

274 m/s²27.9 g

Photosphere temperature

≈ 5,500°C5,772 K

Core temperature

≈ 15 million °C

Corona temperature

1–3 million °C

Mean distance from Earth

1 AU≈ 149.6 million km

Rotation

≈ 25 daysAt the equator; ≈ 35 days near the poles

Age

≈ 4.6 billion years

Spectral type

G2VYellow dwarf

Composition by mass

73% H · 25% He≈ 2% heavier elements

Luminosity

3.83 × 10²⁶ W

The Sun has no solid surface; “surface” values refer to the photosphere, the layer we see. Values follow the NASA Sun Fact Sheet.

Size, mass and composition

The Sun is about 1.39 million km across, 109 times the width of Earth. About 1.3 million Earths would fit inside it. Even so, astronomers count it as an average-sized star: many stars are much bigger, though most stars in the Milky Way are smaller, dimmer red dwarfs.

The Sun is a ball of hot plasma, gas so hot that its atoms have been stripped of electrons, held together by its own gravity. Gravity at the photosphere is about 28 times Earth's. It has no solid surface. What we see as the edge of the Sun is the photosphere, the layer where the gas becomes thin enough for light to escape into space.

By mass, the Sun is about 73% hydrogen and 25% helium. The remaining 2% is heavier elements such as oxygen, carbon, neon and iron, which astronomers call 'metals'.

Layers of the Sun

Sunspots, flares and the solar cycle

The Sun's magnetic field is generated by moving plasma inside it, and it is constantly being twisted because the Sun rotates faster at its equator (about 25 days) than near its poles (about 35 days). About every 11 years the field becomes so tangled that it flips: the Sun's magnetic north and south poles swap places.

This rhythm is the solar cycle. At solar minimum the Sun may show no sunspots for weeks. At solar maximum it is covered in them and frequently erupts with solar flares, intense bursts of radiation, and coronal mass ejections (CMEs), billions of tonnes of magnetised plasma hurled into space. NASA and NOAA announced in October 2024 that the Sun had reached the maximum period of Solar Cycle 25.

When a CME reaches Earth it can trigger geomagnetic storms. These produce bright auroras far from the poles, but they can also disrupt satellites, GPS, radio communications and power grids. Forecasting this space weather is one of the main practical reasons for studying the Sun.

The Sun and its planets

The Sun constantly sends out a stream of charged particles called the solar wind, at roughly 400 to 800 km/s. This wind inflates a vast bubble around the Solar System called the heliosphere, which shields the planets from much of the cosmic radiation in interstellar space. Voyager 1 crossed its outer edge, the heliopause, in 2012, and Voyager 2 followed in 2018.

The Sun's brightness sets the habitable zone, the range of distances where a planet like Earth could keep liquid water on its surface. Earth sits comfortably inside it. Venus, closer in, became a runaway greenhouse, and Mars, farther out, lost most of its atmosphere and froze.

The Sun is not fixed either. It orbits the centre of the Milky Way about 26,000 light-years away, at roughly 230 km/s, and completes one lap every 230 million years or so.

Past and future of the Sun

The Sun formed about 4.6 billion years ago from a collapsing cloud of gas and dust. The leftover disc of material around the young Sun went on to form the planets. Since then it has spent its life steadily fusing hydrogen into helium, and it has grown about 30% brighter along the way.

It is roughly halfway through this stable stage. In around 5 billion years, once the hydrogen in its core runs out, the Sun will swell into a red giant, possibly large enough to swallow Mercury, Venus and perhaps Earth. It will then shed its outer layers as a glowing planetary nebula, and its core will remain as a white dwarf about the size of Earth that slowly cools over billions of years. The Sun is not massive enough to explode as a supernova.

Exploration and missions

The Sun has been watched for as long as humans have looked at the sky, but looking at it closely means leaving Earth's atmosphere or building telescopes that can take its heat. Today a fleet of spacecraft watches it around the clock.

1. 1973–1974

   Skylab · NASA

   Astronauts on America's first space station used its Apollo Telescope Mount to take detailed X-ray and ultraviolet images of the Sun.

2. 1974–1986

   Helios 1 & 2 · NASA / West Germany

   A pair of probes that flew closer to the Sun than Mercury and held the record for the closest approach for over 40 years.

3. 1990–2009

   Ulysses · ESA / NASA

   The first spacecraft to fly over the Sun's poles, mapping the solar wind in three dimensions.

4. 1995–

   SOHO · ESA / NASA

   Has watched the Sun from the L1 point between Earth and the Sun for three decades. It also became the most prolific comet discoverer in history.

5. 2010–

   Solar Dynamics Observatory · NASA

   Takes high-resolution images of the whole Sun in many wavelengths every few seconds, tracking its magnetic activity.

6. 2018–

   Parker Solar Probe · NASA

   The first spacecraft to fly through the corona. On 24 December 2024 it passed just 6.1 million km from the Sun's surface at about 690,000 km/h, faster than any human-made object.

7. 2020–

   Solar Orbiter · ESA / NASA

   Gradually tilting its orbit out of the plane of the planets, it took the first-ever images of the Sun's poles in 2025.

8. 2023–

   Aditya-L1 · ISRO

   India's first solar observatory, studying the corona and solar wind from the L1 point since early 2024.

Surprising facts about the Sun

• About 1.3 million Earths could fit inside the Sun.
• The Sun holds 99.86% of all the mass in the Solar System.
• Sunlight takes about 8 minutes to reach Earth, but its energy may have spent more than 100,000 years escaping from the core.
• The Sun's outer atmosphere, the corona, is hundreds of times hotter than its visible surface.
• Seen from space, the Sun is white. It looks yellow from the ground because our atmosphere scatters away some of its blue light.
• Total solar eclipses happen because the Sun is about 400 times wider than the Moon and also about 400 times farther away.

The Sun compared with Earth

Frequently asked questions

How hot is the Sun?

The visible surface (photosphere) is about 5,500°C. The core reaches about 15 million °C, and the outer atmosphere, the corona, is between 1 and 3 million °C.

How far is the Sun from Earth?

On average about 149.6 million km, a distance defined as one astronomical unit (AU). Light covers it in about 8 minutes and 20 seconds.

What is the Sun made of?

Mostly hydrogen (about 73% by mass) and helium (about 25%), with small amounts of heavier elements such as oxygen, carbon, neon and iron, all in the form of plasma.

How old is the Sun and how long will it last?

The Sun is about 4.6 billion years old. It has enough hydrogen to keep shining steadily for about another 5 billion years before it becomes a red giant and then a white dwarf.

Is the Sun a star?

Yes. The Sun is a G-type main-sequence star (G2V), often called a yellow dwarf. It looks so much brighter than other stars only because it is so much closer.

Keep exploring

• Mercury: the swift, scorched innermost world
• Earth: the ocean world that supports life
• Jupiter: king of the planets
• Parker Solar Probe: the spacecraft that touched the sun
• Solar Orbiter: the first views of the sun's poles
• Betelgeuse: what a dying, swollen star looks like
• Sirius B: the white dwarf the Sun will one day become
• See the Sun up close in the interactive 3D solar system
• The Sun and all eight planets of the Solar System

Sources

• NASA Sun Fact Sheet
• NASA Science — The Sun
• ESA — Solar Orbiter