The Sun is the star at the center of the solar system, around which Earth and other planets revolve. It is the solar system's dominant and most massive body, with a radius 109 times that of Earth. The Sun's mass is 330,000 times that of Earth and accounts for more than 99 percent of the solar system’s total mass. The Sun is composed of hot gases containing elements like hydrogen , helium , calcium , sodium , magnesium , and iron . The process of energy generation results from the enormous pressure and density at the centre of the Sun, which makes it possible for nuclei to overcome electrostatic repulsion. The Sun has been shining for 4.6 billion years.

Where is the Sun located in our solar system?

The Sun is located near the edge of the Milky Way Galaxy , approximately 25,000 light-years from the Galaxy's center. Within our solar system, the Sun's immense mass, which accounts for over 99% of the solar system's total mass, creates a gravitational dominance that keeps all the planets, including Earth, in orbit around it. The Earth orbits the sun in an elliptical path.

What is the Sun made of?

The Sun is a star primarily composed of hot gases, including hydrogen and helium, along with smaller amounts of elements like calcium, sodium, magnesium, and iron. The Sun's core is hot enough to sustain nuclear fusion, where hydrogen atoms convert into helium, releasing vast amounts of energy. This process involves the fusion of hydrogen nuclei into helium, with about 0.7 percent of the mass converting into energy, according to Einstein's formula (E = mc^2). The Sun is at least 90 percent hydrogen by the number of atoms. The energy produced in the core travels outward, initially as gamma rays and kinetic energy. As the energy reaches the Sun's surface, known as the photosphere, it appears as visible light with a temperature of about 5,800 K.

How does the Sun produce energy?

The Sun produces energy through nuclear fusion, primarily by converting hydrogen atoms into helium. This process, known as the proton-proton chain reaction, occurs in the Sun's core where extreme pressure and density enable nuclei to overcome electrostatic repulsion. In this process, four hydrogen nuclei fuse to form one helium nucleus, releasing energy as gamma rays and kinetic energy. About 0.7 percent of the original mass is converted into energy, following Einstein's formula (E = mc^2). This conversion of mass to energy allows the Sun to radiate energy for billions of years. The energy generated in the core gradually makes its way to the surface through radiation and convection, eventually being emitted as light and heat.

How does the Sun affect life on Earth?

The Sun is essential for life on Earth, providing light, heat, and energy that drives our atmosphere, climate, and various biological processes. The Sun's energy, produced through nuclear fusion, radiates into space, with Earth intercepting a small fraction. This solar energy powers atmospheric winds, oceanic currents, and nearly all biospheric activity, sustaining life through photosynthesis in plants, algae, and bacteria. The tilt of Earth's axis causes seasons by changing how directly sunlight hits each hemisphere, influencing temperature and climate . Additionally, the Sun emits ultraviolet radiation , which can be both harmful (causing sunburn and increasing skin cancer risk) and beneficial (stimulating vitamin D production).

What are some important features of the Sun, like sunspots or solar flares?

The Sun has several notable features related to its magnetic activity. Sunspots are regions of strong magnetic fields on the Sun's surface that appear as dark spots because they are cooler than the surrounding photosphere . Solar flares are sudden bursts of energy that occur near sunspot groups, releasing high-energy particles, X-rays, and radio bursts. Flares occur in the corona, and the energy released heats the surface, creating a superhot cloud that emits X-rays. These phenomena follow an 11-year cycle , with the number and size of sunspots and flares fluctuating.

Sun

Images, Videos & Interactives

The black silhouette of a man standing in front of high resolution NASA images of the Sun.

Interactive comparing planet sizes in the solar system from left to right: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

Explore the physics behind nuclear fusion and the Sun

A timeline diagram illustrates the life cycle of a medium-sized star, showing its progression from a cloud of hydrogen and dust, to a main-phase star like the Sun, then to a red giant, and finally collapsing into a white dwarf, with each stage labeled and depicted by a glowing sphere.

At a Glance

Sun summary

Sun

astronomy

Written by

Harold ZirinAll

Fact-checked by

Britannica Editors

Last updated

Nov. 12, 2026 •History

News •

NASA’s Parker Solar Probe discovers a hidden pattern in the Sun’s chaotic magnetic fields • Nov. 11, 2026, 9:36 PM ET (Science Daily)

Scientists Simulated Solar Explosions in The Lab – And May Have Solved One of The Sun's Biggest Mysteries • Oct. 25, 2026, 5:01 AM ET (ScienceAlert)

Sun, star around which Earth and the other components of the solar system revolve. It is the dominant body of the system, constituting more than 99 percent of its entire mass. The Sun is the source of an enormous amount of energy, a portion of which provides Earth with the light and heat necessary to support life. It is part of the "observable universe," the region of space that humans can actually or theoretically observe with the aid of technology. Unlike the observable universe, the universe is possibly infinite.

(List of Brightest Stars as Seen from Earth)

The Sun is classified as a G2 V star, with G2 standing for the second hottest stars of the yellow G class—of surface temperature about 5,800 kelvins (K)—and the V representing a main sequence, or dwarf, star, the typical star for this temperature class. (G stars are so called because of the prominence of a band of atomic and molecular spectral lines that the German physicist Joseph von Fraunhofer designated G.) The Sun exists in the outer part of the Milky Way Galaxy and was formed from material that had been processed inside a supernova. The Sun is not, as is often said, a small star. Although it falls midway between the biggest and smallest stars of its type, there are so many dwarf stars that the Sun falls in the top 5 percent of stars in the neighbourhood that immediately surrounds it.

By clicking “Sign Up”, you consent to the Britannica Privacy Policy and Terms of Use.

Physical properties

Inland SeaSunset on the Inland Sea, with the Seto Great Bridge in the foreground.

The radius of the Sun, R_☉, is 109 times that of Earth, but its distance from Earth is 215 R_☉, so it subtends an angle of only 1/2° in the sky, roughly the same as that of the Moon. By comparison, Proxima Centauri, the next closest star to Earth, is 250,000 times farther away, and its relative apparent brightness is reduced by the square of that ratio, or 62 billion times. The temperature of the Sun’s surface is so high that no solid or liquid can exist there; the constituent materials are predominantly gaseous atoms, with a very small number of molecules. As a result, there is no fixed surface. The surface viewed from Earth, called the photosphere, is the layer from which most of the radiation reaches us; the radiation from below is absorbed and reradiated, and the emission from overlying layers drops sharply, by about a factor of six every 200 kilometres (124 miles). The Sun is so far from Earth that this slightly fuzzy surface cannot be resolved, and so the limb (the visible edge) appears sharp.

The mass of the Sun, M_☉, is 743 times the total mass of all the planets in the solar system and 330,000 times that of Earth. All the interesting planetary and interplanetary gravitational phenomena are negligible effects in comparison to the force exerted by the Sun. Under the force of gravity, the great mass of the Sun presses inward, and to keep the star from collapsing, the central pressure outward must be great enough to support its weight. The density at the Sun’s core is about 100 times that of water (roughly six times that at the centre of Earth), but the temperature is at least 15,000,000 K, so the central pressure is at least 10,000 times greater than that at the centre of Earth, which is 3,500 kilobars. The nuclei of atoms are completely stripped of their electrons, and at this high temperature they collide to produce the nuclear reactions that are responsible for generating the energy vital to life on Earth.

Britannica Quiz

27 True-or-False Questions from Britannica’s Most Difficult Science Quizzes

While the temperature of the Sun drops from 15,000,000 K at the centre to 5,800 K at the photosphere, a surprising reversal occurs above that point; the temperature drops to a minimum of 4,000 K, then begins to rise in the chromosphere, a layer about 7,000 kilometres high at a temperature of 8,000 K. During a total eclipse the chromosphere appears as a pink ring. Above the chromosphere is a dim, extended halo called the corona, which has a temperature of 1,000,000 K and reaches far past the planets. Beyond a distance of 5R_☉ from the Sun, the corona flows outward at a speed (near Earth) of 400 kilometres per second (km/s); this flow of charged particles is called the solar wind.

The Sun is a very stable source of energy; its radiative output, called the solar constant, is 1.366 kilowatts per square metre at Earth and varies by no more than 0.1 percent. Superposed on this stable star, however, is an interesting 11-year cycle of magnetic activity manifested by regions of transient strong magnetic fields called sunspots.

Explore Britannica Premium!

The trusted destination for professionals, college students, and lifelong learners.

Sun

News •

Thank you for signing up!

Physical properties