The Sun is the star at the center of our solar system. Every planet, moon, comet, and asteroid in our cosmic neighborhood orbits around it. Without the Sun's heat and light, life on Earth would not exist. It is the biggest and hottest object in the solar system, and scientists have studied it for thousands of years.

How Big Is the Sun?

The Sun is the biggest object in our solar system. Its radius stretches about 432,288 miles (695,700 km) from the center to the surface. That means it is about 109 times wider than Earth. To give you a picture of just how enormous that is, roughly 1.3 million Earths could fit inside the Sun.

Even with all that size, the Sun is actually an average-sized star. Some stars in the universe are only about a tenth of the Sun's size. Others are more than 700 times bigger. The Sun's massive size and powerful gravity pull it into its nearly perfect sphere shape. It is so round that scientists consider it the most perfectly round natural object ever observed.

How Hot Is the Sun?

The hottest part of the Sun is its core, where temperatures reach about 27,000,000°F (15,000,000°C). That is hot enough to power a process called thermonuclear fusion, where hydrogen atoms are smashed together to form helium atoms. This reaction releases an extraordinary amount of energy as heat and light.

The energy produced in the core can take up to a million years to travel outward through the Sun's layers. By the time it reaches the surface, the temperature has dropped to about 10,422°F (5,772°C). That may sound cool compared to the core, but it is still hot enough to boil diamonds.

Here is one of the Sun's biggest mysteries. In the Sun's outermost atmosphere, called the corona, the temperature shoots back up to roughly 3,600,000°F (2,000,000°C). In some areas, it can reach 14,400,000°F to 36,000,000°F (8,000,000°C to 20,000,000°C). Scientists are still trying to figure out why the temperature rises so dramatically the farther you get from the core. Two main ideas have been proposed: "wave heating," where waves from the Sun's interior release energy in the corona, and "magnetic heating," where the Sun's magnetic energy builds up and is released in events like solar flares.

What Is the Sun Made Of?

The Sun is a giant ball of gas and plasma. About 73% of its outer visible layer is hydrogen, and about 25% is helium. All other heavier elements make up less than 2% of the Sun's mass. The most common of these are oxygen (about 1%), carbon (0.3%), neon (0.2%), and iron (0.2%). In total, scientists have detected at least 65 different elements in the Sun.

The Sun's original ingredients came from the giant cloud of gas and dust it formed from. Most of the hydrogen and helium were created during the Big Bang. Heavier elements were made by older stars that exploded before the Sun formed.

Under intense heat and pressure deep inside the Sun, hydrogen is fused into helium during nuclear fusion. Every second, the Sun's core turns about 600 billion kilograms of hydrogen into helium and changes about 4 billion kilograms of matter into pure energy.

When plasma gets heated to these extreme temperatures, some particles gain enough energy to escape the Sun's gravity and blast out into space. This stream of particles is called solar wind. When solar wind hits Earth's atmosphere, it can create beautiful light shows called auroras, like the Northern Lights and the Southern Lights.

How Is the Sun Structured?

The Sun has several layers, kind of like an onion.

The Core

The Sun's core is its very center, reaching out to about a quarter of the Sun's total radius. The core is incredibly dense, about 150 times denser than water. This is the only place in the Sun where nuclear fusion happens. About 99% of the Sun's total power comes from the innermost 24% of its radius. The rate of fusion is naturally balanced — if fusion speeds up, the core heats up and expands, slowing it down. If it slows, the core cools and shrinks, speeding it up. This self-correcting process keeps the Sun stable.

The Radiative Zone

Outside the core is the radiative zone, the thickest layer of the Sun. It extends from about 25% to 70% of the Sun's radius. In this layer, energy moves outward mainly through thermal radiation. Tiny packets of light called photons carry the energy, but they are constantly absorbed and re-emitted by hydrogen and helium particles. It can take a single photon between 10,000 and 170,000 years to travel through this zone to the surface!

The Convective Zone

Above the radiative zone is the convective zone. In this layer, hot gas rises, cools, and then sinks back down, just like boiling water in a pot. This creates huge currents that carry heat to the Sun's surface. The surface of the Sun looks grainy because of these rising and sinking gas cells. This pattern is called solar granulation.

The Photosphere

The photosphere is the visible surface of the Sun. It is the layer where light can finally escape into space. The photosphere has a temperature of about 10,422°F (5,772°C). The Sun appears brighter in the center and slightly darker toward its edges, an effect called limb darkening.

The Chromosphere

Above the photosphere is the chromosphere, about 1,243 miles (2,000 km) thick. It gets its name from the Greek word "chroma," meaning color. It looks like a colored flash during a total solar eclipse. Temperatures here increase with height, reaching about 35,540°F (20,000°C) at the top.

The Corona

The corona is the Sun's outermost atmosphere, with temperatures between 1,800,000°F and 3,600,000°F (1,000,000°C and 2,000,000°C). The corona extends far into space and eventually becomes the solar wind. The Parker Solar Probe has actually flown through the corona, getting closer to the Sun than any other spacecraft in history.

The Heliosphere

The heliosphere is a huge bubble of space around the Sun where the solar wind and magnetic field are stronger than forces from other stars. The Voyager 1 probe crossed its edge in 2012 and is now traveling through interstellar space — the space between stars.

Does the Sun Rotate?

Yes! Even though the Sun is not solid like Earth, it still spins. On average, it takes about 27 Earth days for the Sun to complete one full rotation. But here is the interesting part: different regions rotate at different speeds. Scientists call this differential rotation.

The areas near the equator spin faster, completing a rotation in about 25 days. The polar regions move more slowly, taking about 33 to 34 days. If you looked down on the Sun from above its north pole, it would spin counter-clockwise.

Scientists believe the early Sun spun much faster, maybe ten times faster than today. Its spin slowed over billions of years because of its magnetic field interacting with the solar wind. The very center of the Sun still spins faster than the rest, completing a rotation about once a week.

What Are Sunspots?

Sunspots are cooler patches on the Sun's surface that appear as dark spots against the hotter, brighter plasma surrounding them. They are caused by strong magnetic fields beneath the surface that block some of the heat rising from the core.

Even though sunspots look dark, they are still incredibly hot — around 7,232°F (4,000°C). They just appear dark because the surrounding areas are even hotter. These spots can stretch up to 31,069 miles (50,000 km) across, almost four times the width of Earth!

The number of sunspots changes over time, following an 11-year cycle. At the peak (solar maximum), many sunspots appear. At the lowest point (solar minimum), there are very few. The Sun's overall magnetic field completely flips its polarity every 22 years.

People have observed sunspots for a very long time. Chinese astronomers recorded them as early as the Han dynasty (202 BC to 220 AD). When the telescope was invented in the early 1600s, scientists like Galileo Galilei studied them in much greater detail. During the 17th century, a period of very few sunspots called the Maunder Minimum coincided with a "Little Ice Age" in Europe.

What Are Solar Flares?

Solar flares are the largest explosive events in the entire solar system. They happen when magnetic fields near sunspots suddenly convert their stored energy into heat and shoot particles into space.

Solar flares release a burst of light at almost every wavelength, from visible light to ultraviolet rays, X-rays, and gamma rays. They can last from just a couple of minutes to a few hours. The Sun also produces coronal mass ejections — huge bubbles of plasma and magnetic field that erupt outward. When these particles reach Earth, they can disrupt radio signals and power grids, but they also create stunning aurora displays.

What Type of Star Is the Sun?

The Sun is classified as a yellow dwarf, also known as a G-type main-sequence star. Like all stars, it started as a collapsing cloud of dust and gas called a nebula. As the particles pulled together under gravity, the mass heated up and became a protostar. Once hot enough, nuclear fusion began, turning hydrogen into helium. That is how the Sun was born about 4.6 billion years ago.

Right now, the Sun is in its main sequence stage — the long, stable part where the outward push of fusion perfectly balances the inward pull of gravity. The Sun has been here for 4.6 billion years and will remain stable for about 5 billion more. It is slowly getting brighter: since it began, its radius has grown by 15% and it has become about 48% brighter.

What Will Happen to the Sun?

The Sun will not explode. It is not massive enough for a supernova. In about 5 billion years, it will run out of hydrogen fuel in its core. The outer layers will collapse, creating temperatures hot enough to fuse helium into carbon, causing the Sun to expand into a red giant.

As a red giant, the Sun will grow about 256 times larger than today. It will likely swallow Mercury and Venus, and may even reach Earth. After about a billion years in this phase, the helium will ignite in a "helium flash." The Sun will eventually shed its outer layers, forming a glowing planetary nebula. What remains will be a small, dense white dwarf, containing about 54% of the Sun's original mass. It will slowly cool for trillions of years.

Where Is the Sun in the Milky Way?

Our Sun lives inside the Milky Way galaxy — one of an estimated 100 billion galaxies in the known universe. The Milky Way stretches about 100,000 light-years across.

The Sun sits in a spiral arm called the Orion Spur, branching off the Sagittarius Arm. Our entire solar system orbits the center of the Milky Way at about 447,387 miles per hour (720,000 km/h). Even at that speed, it takes about 225 to 250 million years to complete one full orbit — called a galactic year. The Sun has completed about 20 of these orbits since it was born.

Eight planets orbit the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. The solar system also includes dwarf planets, an asteroid belt, comets, and icy bodies beyond Neptune. The Sun's gravity controls objects out to about two light-years away.

What Is a Solar Eclipse?

A solar eclipse happens when the Moon passes directly between the Sun and Earth, blocking the Sun's light and casting a shadow on our planet.

This is possible because of an amazing coincidence: the Sun is about 400 times larger than the Moon, but the Moon is about 400 times closer to Earth. So from our perspective, they appear almost exactly the same size in the sky.

Solar eclipses happen roughly every six months. Total solar eclipses, where the Moon completely covers the Sun, are much rarer — only about once every two years, and often visible only from remote areas. A total eclipse can last from a few seconds up to about seven minutes. During one, you can see the corona glowing around the Moon's edges.

How Do We Study the Sun?

Sending spacecraft close to the Sun is extremely difficult because of the extreme heat. For most of history, scientists relied on telescopes and cameras on Earth and orbiting satellites.

The first satellites to study the Sun were NASA's Pioneer 6, 7, 8, and 9 probes, launched between 1959 and 1968. In 1995, the Solar and Heliospheric Observatory (SOHO) was launched, sitting at a special point between Earth and the Sun for a constant view of our star.

In 2020, the European Space Agency and NASA launched the Solar Orbiter. It travels as close as 26 million miles (42 million km) from the Sun's surface — closer than Mercury. Over its seven-year mission, it is studying the Sun's solar wind, magnetic fields, and plasma.

The Sun in Culture and Beliefs

The Sun has been incredibly important in religions and myths around the world for thousands of years. The ancient Egyptians honored the Sun god Ra. The Incas and Aztecs worshipped the Sun at the center of their beliefs. In Hinduism, the Sun is still seen as a god named Surya. In ancient Greek religion, the Sun god was Helios, later linked with Apollo. In Japanese Shinto, the sun goddess Amaterasu is the most important deity.

Many ancient monuments were built to align with the Sun's movements. Stonehenge in England and Newgrange in Ireland line up with the Sun during the solstices. The pyramid of El Castillo in Mexico creates serpent-shaped shadows during the equinoxes.

The element helium gets its name from the Sun! In 1868, scientist Norman Lockyer noticed lines in the Sun's light spectrum that matched no known element. He named this new element helium, after Helios, the Greek Sun god. Twenty-five years later, helium was finally found on Earth too. Even "Sunday" comes from the ancient Roman tradition of naming days after celestial objects.