The Sun is the star at the center of our Solar System. It is a G2V main-sequence star about 4.6 billion years old, made mostly of hydrogen and helium. Located an average of about 93 million miles (150 million km) from Earth, the Sun provides the light and energy that make life on our planet possible.
The Sun is by far the largest and most massive object in the Solar System, containing about 99.8% of its total mass. Its gravity keeps the planets and countless smaller objects in orbit, while energy produced by nuclear fusion deep inside its core eventually reaches space as sunlight and other forms of radiation. The Sun is also magnetically active, producing sunspots, solar flares, coronal mass ejections and the solar wind.
Although the Sun looks very different from the stars we see at night, that is mainly because it is so much closer to Earth. Studying it gives astronomers an exceptionally detailed view of how a star works, from the nuclear reactions in its core to the vast outer atmosphere that extends into space.
Solar viewing safety: Never look directly at the Sun without proper solar-viewing eye protection. Regular sunglasses are not safe. Binoculars, telescopes and cameras require a special-purpose solar filter secured over the front of the optics.
Sun Facts at a Glance
| Property | The Sun |
|---|---|
| Star type | G2V main-sequence star |
| Age | About 4.6 billion years |
| Distance from Earth | About 93 million miles (150 million km), or 1 AU |
| Diameter | About 865,000 miles (1.39 million km) |
| Mass | About 1.99 × 1030 kg, or 333,000 Earth masses |
| Composition | Mostly hydrogen and helium |
| Photosphere temperature | About 9,900°F (5,500°C) |
| Core temperature | About 27 million°F (15 million°C) |
| Rotation | About 25 days at the equator and 36 days at the poles |
| Galaxy | Milky Way |
| Current life stage | Main sequence |
What Type of Star Is the Sun?
The Sun is a G2V main-sequence star, commonly described as a G-type or yellow dwarf star. The classification G2V tells astronomers about both the Sun’s temperature and its current stage of stellar evolution.
The G2 part is its spectral classification. Stars are divided into spectral classes according to characteristics of their light that are closely related to surface temperature, with the main sequence running from hot O-type stars through B, A, F, G and K stars to much cooler M-type red dwarfs. The Sun falls within the G class and has an effective temperature of about 5,772 K. You can see how the Sun fits into the wider system in our guide to the different types of stars.
The V is the Roman numeral for luminosity class V, identifying the Sun as a main-sequence star. This means it is in the long, stable period of its life during which nuclear fusion in its core converts hydrogen into helium. The Sun has spent most of its roughly 4.6-billion-year existence in this stage and will remain a main-sequence star for several billion more years.
Despite often being called a yellow dwarf, the Sun is not simply a yellow star. Sunlight contains wavelengths from across the visible spectrum that combine to appear essentially white. Its familiar yellow, orange or red appearance from Earth can be influenced by our atmosphere, particularly when the Sun is low in the sky.
The Sun is also sometimes described as an average or medium-sized star. That can be misleading without context. Many stars are substantially larger and more massive, but most stars in the Milky Way are smaller, cooler red dwarfs. The Sun is therefore fairly ordinary in some respects, but larger and more massive than most stars in our galaxy.
How Big Is the Sun?
The Sun has a diameter of about 865,000 miles (1.39 million km), making it by far the largest object in the Solar System. It is about 109 times wider than Earth, and its volume is large enough to contain about 1.3 million Earths.
The difference in mass is even more important. The Sun has a mass of about 1.99 × 1030 kg, or roughly 333,000 times the mass of Earth. In fact, the Sun contains about 99.8% of all the mass in the Solar System. This enormous concentration of mass gives the Sun the gravitational influence that keeps the planets, dwarf planets, asteroids, comets and other Solar System objects in orbit.
Unlike Earth, the Sun does not have a solid surface or sharply defined outer edge. It is an enormous sphere of plasma whose density decreases outward. The radius normally given for the Sun—about 432,000 miles (695,700 km)—is based on its visible layer, the photosphere, which is what we usually perceive as the Sun’s surface.
Despite being made of plasma and rotating at different rates at different latitudes, the Sun is remarkably close to spherical. Its enormous gravity pulls its material inward toward its center, while pressure within the Sun acts outward, helping maintain its stable structure.
What Is the Sun Made Of?
The Sun is made overwhelmingly of hydrogen and helium, along with much smaller amounts of heavier elements such as oxygen, carbon, neon and iron. By mass, roughly three-quarters of the Sun is hydrogen and most of the remainder is helium, with heavier elements accounting for only a small fraction of its total mass.
The material inside the Sun is not an ordinary gas. Temperatures are so high that atoms become ionized, meaning electrons are separated from their nuclei. This electrically charged state of matter is known as plasma and makes up most of the Sun.
The Sun’s composition is fundamental to the way it works. Hydrogen provides the fuel for nuclear fusion in the core, where extreme temperature and pressure allow reactions that ultimately turn hydrogen into helium and release enormous quantities of energy.
How Does the Sun Produce Energy?
The Sun shines because of nuclear fusion taking place deep inside its core. The core has a temperature of about 27 million°F (15 million°C) and is under immense pressure caused by the weight of the material above it.
Under these extreme conditions, hydrogen nuclei can take part in a series of reactions known as the proton-proton chain. The overall result is that hydrogen is converted into helium. The helium produced has slightly less mass than the hydrogen particles that ultimately went into making it. That small difference in mass is converted into energy in accordance with Einstein’s famous relationship between mass and energy, E = mc².
The amount of mass converted during each reaction is tiny, but fusion occurs on such an enormous scale that the Sun continuously produces a vast amount of energy. This process has powered the Sun for billions of years.
Energy produced in the core does not travel straight into space. It must first make its way through the Sun’s interior. In the radiative zone, energy moves outward mainly through interactions between radiation and the dense solar plasma. Farther out, in the convection zone, hot plasma rises toward the surface while cooler plasma sinks, carrying energy outward.
Eventually that energy reaches the photosphere, from where much of it escapes into space as electromagnetic radiation. Sunlight then takes only about eight minutes to cross the roughly 93 million miles between the Sun and Earth.
The Layers of the Sun
Although the Sun has no solid surface, it has a well-defined internal structure and atmosphere. Its principal regions can be divided into the core, radiative zone, convection zone, photosphere, chromosphere, transition region and corona.
Core
The core is the central and hottest part of the Sun. It extends outward through roughly the innermost quarter of the solar radius and is the only region where temperatures and pressures are high enough for significant nuclear fusion to occur.
At around 27 million°F (15 million°C), the core is the source of the energy that ultimately powers almost everything we see happening at the Sun’s surface and beyond.
Radiative Zone
Surrounding the core is the radiative zone. Energy moves through this region primarily by radiation, with photons repeatedly interacting with the dense solar material rather than simply traveling in a straight line toward the surface.
As a result, the journey through the Sun’s interior is extraordinarily slow compared with the final trip from the Sun to Earth.
Convection Zone
Above the radiative zone lies the convection zone. Here convection becomes an efficient way of transporting energy.
Hot plasma rises, releases energy nearer the surface and then sinks again as it cools. This continual motion helps produce the mottled, granular appearance visible in detailed images of the photosphere.
Photosphere
The photosphere is the visible layer of the Sun and what we normally think of as its surface. It is not solid: it is the region from which most of the visible sunlight that escapes the Sun is emitted.
Its temperature is about 9,900°F (5,500°C), far cooler than the core but still hot enough to make the Sun shine intensely.
Chromosphere and Transition Region
Above the photosphere is the chromosphere, a relatively thin layer of the solar atmosphere. Its name means “sphere of color,” reflecting the reddish appearance it can display under suitable observing conditions, particularly during a total solar eclipse.
Above it lies the extremely thin transition region, where temperatures rise dramatically as the solar atmosphere changes into the corona.
Corona
The corona is the Sun’s extended outer atmosphere. It is normally overwhelmed by the much brighter photosphere but can become spectacularly visible around the dark disk of the Moon during a total solar eclipse.
Remarkably, the corona can reach temperatures of about 2 million°C (3.5 million°F), making it vastly hotter than the photosphere beneath it. Understanding exactly how energy is transferred into the corona and heats it to such extreme temperatures remains an important area of solar research.
How Hot Is the Sun?
There is no single answer to the question “How hot is the Sun?” because temperatures vary enormously between its different regions.
The core reaches about 27 million°F (15 million°C), making nuclear fusion possible. Temperatures decrease moving outward through much of the interior until reaching about 9,900°F (5,500°C) in the photosphere.
Above the photosphere, however, the pattern reverses. Temperatures begin to rise through the chromosphere and transition region, and the corona can reach about 2 million°C (3.5 million°F).
This apparently counterintuitive increase is known as the coronal heating problem. The Sun’s magnetic field plays a central role, with processes involving magnetic waves and magnetic reconnection among the mechanisms thought to transfer energy into the outer atmosphere. Solar observations continue to investigate exactly how these processes combine to produce the extraordinarily hot corona.
What Color Is the Sun?
The Sun is commonly represented as yellow and belongs to a class of stars often called yellow dwarfs, but sunlight itself appears essentially white when viewed without the coloring effects of Earth’s atmosphere.
The Sun emits energy across a broad range of wavelengths, including the full visible spectrum. When those visible wavelengths are perceived together by human vision, they produce white light rather than a single spectral color.
Earth’s atmosphere can change how the Sun appears. When the Sun is low in the sky, its light travels through more atmosphere before reaching us. Shorter wavelengths of visible light are scattered more strongly, leaving proportionally more of the longer wavelengths traveling directly toward the observer. This is why the Sun can appear yellow, orange or deep red near sunrise and sunset.
The term yellow dwarf is therefore a useful conventional label for a class of stars, not a literal description of the Sun’s color as seen from space.
The Sun’s Magnetic Activity
The Sun may look steady from Earth, but it is a highly dynamic and magnetically active star. Motions of electrically conducting plasma inside the rotating Sun generate and continually reshape a complex magnetic field.
Much of the changing activity we see on the Sun is associated with this magnetic field.
Sunspots and the Solar Cycle
Sunspots are darker regions on the photosphere associated with particularly strong magnetic fields. They look dark because they are cooler than the surrounding photosphere, although they are still extremely hot.
The number of visible sunspots rises and falls as part of the solar cycle, which lasts about 11 years on average. During solar minimum, relatively few sunspots are visible. Activity then increases toward solar maximum, when sunspots and energetic solar events become more common.
The Sun’s global magnetic polarity also reverses during this cycle. A full magnetic cycle, in which the magnetic field returns to its original polarity, therefore takes about 22 years.
Solar Flares and Coronal Mass Ejections
Disturbances in the Sun’s magnetic field can produce sudden and powerful events.
A solar flare is a rapid release of energy that produces intense electromagnetic radiation. A coronal mass ejection (CME), by contrast, is a huge eruption of magnetized plasma from the Sun’s corona into space.
Flares and CMEs can occur together, but they are not the same phenomenon. When sufficiently powerful eruptions are directed toward Earth, they can disturb the space environment surrounding our planet.
Solar Wind and the Heliosphere
The Sun’s influence does not end at the corona. Its hot outer atmosphere continually releases a stream of charged particles known as the solar wind, which flows outward through the Solar System.
The solar wind carries the Sun’s magnetic field with it and interacts with planets, moons and other bodies along the way. At Earth, our planet’s magnetic field deflects much of this stream, while interactions between solar particles and Earth’s upper atmosphere can help produce the auroras seen near the polar regions.
As the solar wind expands outward, it creates an enormous region dominated by the Sun’s plasma and magnetic influence called the heliosphere. This bubble surrounds the planets and extends well beyond the orbit of Neptune before eventually meeting the interstellar environment.
In this sense, the Solar System exists not only within the Sun’s gravitational domain but also inside an enormous magnetic and particle environment created by our star.
How Does the Sun Affect Earth and the Solar System?
The Sun dominates the Solar System in several different ways. Most obviously, its enormous mass produces the gravity that keeps Earth and the other planets in orbit. Without the Sun, the planetary system as we know it would not exist.
The Sun is also Earth’s main external source of energy. Solar radiation warms the planet and powers processes throughout Earth’s atmosphere, oceans and living systems. Plants use sunlight for photosynthesis, forming the energetic foundation of most ecosystems on Earth.
The changing seasons are not caused by Earth becoming significantly closer to or farther from the Sun during its orbit. Instead, they result primarily from the tilt of Earth’s rotational axis, which changes the angle and duration of sunlight received by each hemisphere during the year.
The Sun can also affect modern technology through space weather. Solar flares and Earth-directed CMEs can disturb Earth’s magnetic environment and upper atmosphere, potentially affecting satellites, radio communications, navigation systems and, during particularly strong geomagnetic storms, electrical power systems.
The same interactions can intensify auroras, sometimes allowing them to be seen much farther from the polar regions than usual.
How Did the Sun Form?
The Sun formed about 4.6 billion years ago from material within a large cloud of gas and dust in space.
Part of this cloud collapsed under gravity. As the material contracted, it began rotating more rapidly and flattened into a disk. Most of the mass accumulated near the center, forming the proto-Sun, while the surrounding disk contained the material from which the planets, moons, asteroids, comets and other Solar System bodies would eventually develop.
As the proto-Sun continued contracting, its central temperature and pressure increased. Eventually conditions in the core became extreme enough for sustained hydrogen fusion to begin. At that point, the young Sun entered the main sequence, the long-lived stage of stellar evolution it remains in today.
The Sun and planets therefore share a common origin. Their different compositions and structures developed from the same broad process of Solar System formation, although most of the original material ended up in the Sun itself.
What Will Happen to the Sun in the Future?
The Sun will not remain as it is forever. Like other stars, it changes as it consumes the nuclear fuel available in its core.
The Sun is currently a little less than halfway through its expected lifetime and should continue fusing hydrogen in its core for around another 5 billion years. During this long period, its luminosity will gradually increase.
Long before the Sun reaches the end of the main sequence, that increasing luminosity will make conditions on Earth progressively less hospitable to life. The exact future of Earth’s climate and oceans depends on complex processes and should not be reduced to a single precise date, but our planet will become uninhabitable well before the Sun itself reaches the end of its life.
Once the hydrogen available for fusion in the core becomes depleted, the Sun’s internal structure will change dramatically. Its outer layers will expand and cool as it develops into a red giant, becoming vastly larger than it is today. Mercury and Venus will be engulfed. Whether Earth itself ultimately survives outside the expanding solar atmosphere or is engulfed is less certain, although it would already have been uninhabitable for a very long time.
The Sun is not massive enough to explode as a supernova. Instead, during its later evolution it will shed its outer layers into space, producing a glowing planetary nebula. The hot exposed core left behind will become a white dwarf.
That white dwarf will no longer generate substantial energy through nuclear fusion. It will instead cool extremely slowly over immense periods of time. You can follow this entire process in our guide to the life cycle of a star.
Where Is the Sun in the Milky Way?
The Sun is one of the enormous number of stars that make up the Milky Way galaxy. It lies in a smaller spiral feature of the galaxy known as the Orion Spur.
The entire Solar System moves through the galaxy with the Sun. Our star orbits the center of the Milky Way from a distance of roughly 26,000 light-years, traveling at hundreds of thousands of miles per hour.
Even at that speed, the Milky Way is so vast that one complete orbit takes roughly 230 million years. The Sun has therefore completed only around 20 galactic orbits since it formed.
Is the Sun Also Called Sol?
The Sun’s normal English name is simply the Sun. You may also encounter the name Sol, particularly in science fiction and occasionally when distinguishing our Sun from other stars.
Sol is the Latin word for Sun and is the origin of English words such as solar. It should not, however, be regarded as a special official scientific name that astronomers are required to use for our star.
The word has another astronomical use on Mars. A sol is a Martian solar day, lasting about 24 hours and 39 minutes, and the term is commonly used when describing the activities of spacecraft operating on the Martian surface.
