The Sun: Formation, Facts and Characteristics

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The Sun: Formation, Facts and Characteristics

The sun lies at the heart of the solar system, where it is by far the largest object. It holds 99.8 percent of the solar system’s mass and is roughly 109 times the diameter of the Earth — about one million Earths could fit inside the sun.

The visible part of the sun is roughly 10,000 degrees F (5,500 degrees C), while temperatures in the core reach more than 27 million degrees F (15 million degrees C), driven by nuclear reactions. One would need to explode 100 billion tons of dynamite every second to match the energy produced by the Sun.

The sun is one of more than 100 billion stars in the Milky Way. It orbits some 25,000 light years from the galactic core, completing a revolution once every 250 million years or so. The sun is relatively young, part of a generation of stars known as Population I, which are relatively rich in elements heavier than helium. An older generation of stars is called Population II, and an earlier generation of Population III may have existed, although no members of this generation are known yet.

A huge solar filament snakes around the southwestern horizon of the sun in this full disk photo taken by NASA's Solar Dynamics Observatory on Nov. 17, 2010.

A huge solar filament snakes around the southwestern horizon of the sun in this full disk photo taken by NASA’s Solar Dynamics Observatory on Nov. 17, 2010. 

Formation & Evolution

The sun was born roughly 4.6 billion years ago. Many scientists think the sun and the rest of the solar system formed from a giant, rotating cloud of gas and dust known as the solar nebula. As the nebula collapsed because of its gravity, it spun faster and flattened into a disk. Most of the material was pulled toward the center to form the sun.

The sun has enough nuclear fuel to stay much as it is now for another 5 billion years. After that, it will swell to become a red giant. Eventually, it will shed its outer layers, and the remaining core will collapse to become a white dwarf. Slowly, this will fade, to enter its final phase as a dim, cool object sometimes known as a black dwarf.


  • Internal structure and atmosphere
See how solar flares, sun storms and huge eruptions from the sun work in this infographic. 
CREDIT: Karl Tate/ 

The sun and its atmosphere are divided into several zones and layers. The solar interior, from the inside out, is made up of the core, radiative zone and the convective zone. The solar atmosphere above that consists of the photosphere, chromosphere, a transition region and the corona. Beyond that is the solar wind, an outflow of gas from the corona.

The core extends from the sun’s center to about a quarter of the way to its surface. Although it only makes up roughly 2 percent of the sun’s volume, it isalmost 15 times the density of lead and holds nearly half of the sun’s mass. Next is the radiative zone, which extends from the core to 70 percent of the way to the sun’s surface, making up 32 percent of the sun’s volume and 48 percent of its mass. Light from the core gets scattered in this zone, so that a single photon often may take a million years to pass through. The convection zone reaches up to the sun’s surface, and makes up 66 percent of the sun’s volume but only a little more than 2 percent of its mass. Roiling “convection cells” of gas dominate this zone. Two main kinds of solar convection cells exist — granulation cells about 600 miles (1,000 kilometers) wide and supergranulation cells about 20,000 miles (30,000 kilometers) in diameter.

The photosphere is the lowest layer of the sun’s atmosphere, and emits the light we see. It is about 300 miles (500 kilometers) thick, although most of the light comes from its lowest third. Temperatures there range from 11,000 degrees F (6,125 degrees C) at bottom to 7,460 degrees F (4,125 degrees C) at top. Next up is the chromosphere, which is hotter at up to 35,500 degrees F (19,725 degrees C) and is apparently made up entirely of spiky structures known as spicules typically some 600 miles (1,000 kilometers) across and up to 6,000 miles (10,000 kilometers) high. After that is the transition region a few hundred to a few thousand miles or kilometers thick, which is heated by the corona above it and sheds most of its light as ultraviolet rays. At the top is the super-hot corona, which is made of structures such as loops and streams of ionized gas. The corona generally ranges from 900,000 degrees F (500,000 degrees C) to 10.8 million degrees F (6 million degrees C) and can even reach tens of millions of degrees when a solar flare occurs. Matter from the corona is blown off as the solar wind.

  • Magnetic Field

The strength of the sun’s magnetic field is typically only about twice as strong as Earth’s field. However, it becomes highly concentrated in small areas, reaching up to 3,000 times stronger than usual. These kinks and twists in the magnetic field develop because the sun spins more rapidly at the equator than at the higher latitudes and because the inner parts of the sun rotate more quickly than the surface. These distortions create features ranging from sunspots to spectacular eruptions known as flares and coronal mass ejections. Flares are the most violent eruptions in the solar system, while coronal mass ejections are less violent but involve extraordinary amounts of matter — a single ejection can spout roughly 20 billion tons (18 billion metric tons) of matter into space.

Chemical Composition

Just like most other stars, the sun is made up mostly of hydrogen, followed by helium. Nearly all the remaining matter consists of seven other elements — oxygen, carbon, neon, nitrogen, magnesium, iron and silicon. For every 1 million atoms of hydrogen in the sun, there are 98,000 of helium, 850 of oxygen, 360 of carbon, 120 of neon, 110 of nitrogen, 40 of magnesium, 35 of iron, and 35 of silicon. Still, hydrogen is the lightest of all elements, so it only accounts for roughly 72 percent of the sun’s mass, while helium makes up about 26 percent.

Sunspots & Solar Cycle

Sunspots are relatively cool, dark features on the sun’s surface that are often roughly circular. They emerge where dense bundles of magnetic field lines from the sun’s interior break through the surface. The number of sunspots varies as solar magnetic activity does — the change in this number, from a minimum of none to a maximum of roughly 250 sunspots or clusters of sunspots and then back to a minimum, is known as the solar cycle, and averages about 11 years long. At the end of a cycle, the magnetic field rapidly reverses its polarity.


Ancient cultures often modified natural rock formations or built stone monuments to mark the motions of the sun and moon, charting the seasons, creating calendars and monitoring eclipses. Many believed the sun revolved around the Earth, with ancient Greek scholar Ptolemy formalizing this “geocentric” model in 150. Then, in 1543, Copernicus described a heliocentric, sun-centered model of the solar system, and in 1610, Galileo’s discovery of Jupiter’s moons revealed that not all heavenly bodies circled the Earth.

To learn more about how the sun and other stars work, after early observations using rockets, scientists began studying the sun from Earth orbit. NASA launched a series of eight orbiting observatories known as the Orbiting Solar Observatory between 1962 and 1971. Seven of them were successful, and analyzed the sun at ultraviolet and X-ray wavelengths and photographed the super-hot corona, among other achievements.

In 1990, NASA and the European Space Agency launched the Ulysses probe to make the first observations of its polar regions. In 2004, NASA’s Genesis spacecraft returned samples of the solar wind to Earth for study. In 2007, NASA’s double-spacecraft Solar Terrestrial Relations Observatory (STEREO) mission returned the first three-dimensional images of the Sun.

One of the most important solar missions to date has been the Solar and Heliospheric Observatory (SOHO), which was designed to study the solar wind, as well as the sun’s outer layers and interior structure. It has imaged the structure of sunspots below the surface, measured the acceleration of the solar wind, discovered coronal waves and solar tornadoes, found more than 1000 comets, and revolutionized our ability to forecast space weather. Recently, NASA’s Solar Dynamics Observatory (SDO), the most advanced spacecraft yet designed to study the sun, has returned never-before-seen details of material streaming outward and away from sunspots, as well as extreme close-ups of activity on the sun’s surface and the first high-resolution measurements of solar flares in a broad range of extreme ultraviolet wavelengths.

RELATED: See our overview of Solar System Facts or learn more about the Solar System Planets.

What is the Sun Made Of?

The sun is a big ball of hot gases. The gases are converted into energy in the sun’s core. The energy moves outward through the interior layers, into the sun’s atmosphere, and is released into the solar system as heat and light.

NASA’s Solar Dynamics Observatory saw sunspot AR 1520 before the solar flare erupted from it on July 12, 2012.

Most of the gas — about 72 percent — is hydrogen. Nuclear fusion converts hydrogen into other elements. The sun is also composed of about 26 percent helium and trace amounts of other elements — oxygen, carbon, neon, nitrogen, magnesium, iron and silicon.

These elements are created in the sun’s core, which makes up 25 percent of the sun. Gravitational forces create tremendous pressure and temperatures in the core. The temperature of the sun in this layer is about 27 million degrees F (15 million degrees C). Hydrogen atoms are compressed and fuse together, creating helium and a lot of energy. This process is called nuclear fusion.

The energy, mostly in the form of gamma-ray photons and neutrinos, is carried into the radiative zone. Photons can bounce around in this zone for about a million years before passing through the interface layer, or tachocline. Scientists think the sun’s magnetic field is generated by a magnetic dynamo in this layer.

The convection zone is the outermost layer of the sun’s interior. It extends from about 125,000 miles (200,000 km) deep up to the visible surface or the sun’s atmosphere. Temperatures cool in this zone, enough for heavier ions — such as carbon, nitrogen, oxygen, calcium and iron — to hold onto their electrons. This makes the material more opaque and traps heat, causing the plasma to boil or “convect.”

The convective motions carry heat quite rapidly to the surface, which is the bottom layer of the sun’s atmosphere, or photosphere. This is the layer where the energy is released as sunlight. The light passes through the outer layers of the sun’s atmosphere — the chromosphere and the corona — before reaching Earth eight minutes later.

Abundance of elements

Astronomers who have studied the composition of the sun have catalogued 67 chemical elements in the sun. There may be more, but in amounts too small for instruments to detect. Here is a table of the 10 most common elements in the sun:

Element Abundance (pct.
of total number
of atoms)
(pct. of total mass)
Hydrogen 91.2         71.0        
Helium 8.7         27.1        
Oxygen 0.078         0.97        
Carbon 0.043         0.40        
Nitrogen 0.0088         0.096        
Silicon 0.0045         0.099        
Magnesium 0.0038         0.076        
Neon 0.0035         0.058        
Iron 0.030         0.014        
Sulfur 0.015         0.040        

— Tim Sharp, Reference Editor


What Does the Sun Burn?

By: Benjamin Radford, Life’s Little Mysteries Contributor

Date: 20 December 2012 Time: 04:31 PM ET

For millennia, people have looked up to the sky and wondered about celestial bodies. The sparkling stars and fiery sun hold mystery and wonder. To astronomers, the sun is just another dying star, but to everyone else it’s a huge burning ball that gives heat, light, and life. So far so good.

But what is it burning? We all know that there is no air in space, and therefore no oxygen to burn. In our everyday experience, the only burning most of us are familiar with is fire combustion. But that is not the only type of reaction; the sun is indeed burning, but it is a nuclear reaction, not a chemical one.

The sun burns hydrogen — a lot of it, several hundred million tons per second. But don’t worry; there’s plenty more where that came from; by most estimates, the sun has enough fuel for about another five billion years.


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