Our Sun is a 4.5 billion-year-old yellow dwarf star – a hot glowing ball of hydrogen and helium – at the center of our solar system. It’s about 93 million miles (150 million kilometers) from Earth and it’s our solar system’s only star. Without the Sun’s energy, life as we know it could not exist on our home planet.
The Sun is about 100 times wider than Earth and about 10 times wider than Jupiter, the biggest planet.
The Sun is the only star in our solar system. It is the center of our solar system, and its gravity holds the solar system together. Everything in our solar system revolves around it – the planets, asteroids, comets, and tiny bits of space debris.
Measuring a “day” on the Sun is complicated. The Sun is made of super-hot, electrically charged gas called plasma. This plasma rotates at different speeds on different parts of the Sun. At its equator, the Sun completes one rotation in 25 Earth days. At its poles, the Sun rotates once on its axis every 36 Earth days.
The part of the Sun we see from Earth – the part we call the surface – is the photosphere. The Sun doesn’t actually have a solid surface because it’s a ball of plasma.
Above the Sun’s surface are its thin chromosphere and the huge corona (crown). This is where we see features such as solar prominences, flares, and coronal mass ejections. The latter two are giant explosions of energy and particles that can reach Earth.
The Sun doesn’t have moons, but it’s orbited by eight planets, at least five dwarf planets, tens of thousands of asteroids, and perhaps three trillion comets and icy bodies.
Several spacecraft are currently investigating the Sun including Parker Solar Probe, STEREO, Solar Orbiter, SOHO, Solar Dynamics Observatory, Hinode, IRIS, and Wind.
The Sun would have been surrounded by a disk of gas and dust early in its history when the solar system was first forming 4.6 billion years ago. Some of that dust is still around today, in several dust rings that circle the Sun. They trace the orbits of planets, whose gravity tugs dust into place around the Sun.
Nothing could live on the Sun, but its energy is vital for most life on Earth.
The temperature in the Sun's core is about 27 million degrees Fahrenheit (15 million degrees Celsius) – hot enough to sustain nuclear fusion. This creates outward pressure that supports the star's gigantic mass, keeping it from collapsing.
From our vantage point on Earth, the Sun may appear like an unchanging source of light and heat in the sky. But the Sun is a dynamic star, constantly changing and sending energy out into space. The science of studying the Sun and its influence throughout the solar system is called heliophysics.
The Sun is the largest object in our solar system. Its diameter is about 865,000 miles (1.4 million kilometers). Its gravity holds the solar system together, keeping everything from the biggest planets to the smallest bits of debris in orbit around it.
Even though the Sun is the center of our solar system and essential to our survival, it’s only an average star in terms of its size. Stars up to 100 times larger have been found. And many solar systems have more than one star. By studying our Sun, scientists can better understand the workings of distant stars.
The hottest part of the Sun is its core, where temperatures top 27 million °F (15 million °C). The part of the Sun we call its surface – the photosphere – is a relatively cool 10,000 °F (5,500 °C). In one of the Sun’s biggest mysteries, the Sun’s outer atmosphere, the corona, gets hotter the farther it stretches from the surface. The corona reaches up to 3.5 million °F (2 million °C) – much, much hotter than the photosphere.
The Sun orbits the center of the Milky Way, bringing with it the planets, asteroids, comets, and other objects in our solar system. Our solar system is moving with an average velocity of 450,000 miles per hour (720,000 kilometers per hour). But even at this speed, it takes about 230 million years for the Sun to make one complete trip around the Milky Way.
The Sun rotates on its axis as it revolves around the galaxy. Its spin has a tilt of 7.25 degrees with respect to the plane of the planets’ orbits. Since the Sun is not solid, different parts rotate at different rates. At the equator, the Sun spins around once about every 25 Earth days, but at its poles, the Sun rotates once on its axis every 36 Earth days.
As a star, the Sun doesn’t have any moons, but the planets and their moons orbit the Sun.
The Sun would have been surrounded by a disk of gas and dust early in its history when the solar system was first forming, about 4.6 billion years ago. Some of that dust is still around today, in several dust rings that circle the Sun. They trace the orbits of planets, whose gravity tugs dust into place around the Sun.
The Sun formed about 4.6 billion years ago in a giant, spinning cloud of gas and dust called the solar nebula. As the nebula collapsed under its own gravity, it spun faster and flattened into a disk. Most of the nebula's material was pulled toward the center to form our Sun, which accounts for 99.8% of our solar system’s mass. Much of the remaining material formed the planets and other objects that now orbit the Sun. (The rest of the leftover gas and dust was blown away by the young Sun's early solar wind.)
Like all stars, our Sun will eventually run out of energy. When it starts to die, the Sun will expand into a red giant star, becoming so large that it will engulf Mercury and Venus, and possibly Earth as well. Scientists predict the Sun is a little less than halfway through its lifetime and will last another 5 billion years or so before it becomes a white dwarf.
Sunspots: They look like dark holes in the Sun, but they are actually areas that are slightly cooler than the surrounding photosphere. Sunspots are created where bits of the Sun's magnetic field poke out from the interior into the Sun's atmosphere. Lasting from days to months, sunspots range in size from 1,000 to 100,000 miles (1,600 to 160,900 kilometers).
NASA's Scientific Visualization Studio/SDO
Coronal Holes: A coronal hole is a patch of the Sun’s atmosphere with much lower density than the surrounding areas. In ultraviolet views of the Sun, coronal holes appear as dark splotches. These regions are where the Sun’s magnetic field lines are connected directly to interplanetary space, allowing solar material to escape out in a high-speed stream of solar wind, leaving a dark “hole” near the surface of the Sun.
Solar Flares: Solar flares are tremendously energetic bursts of light and particles triggered by the release of magnetic energy on the Sun. Flares are by far the most powerful explosions in the solar system, with energy releases comparable to billions of hydrogen bombs.
Coronal Mass Ejection (CME): Coronal mass ejections, or CMEs, are immense clouds of magnetized particles blasted into space by the Sun at over a million miles per hour, often following after a solar flare. CMEs expand as they sweep through space, often measuring millions of miles across. When directed at Earth, a CME can produce geomagnetic disturbances that ignite bright auroras, short-circuit satellites, and power grids on Earth, or at their worst, even endanger astronauts in orbit.
ESA/NASA/SOHO
Solar Prominence: A prominence is a snakelike structure made of cooler, denser solar material that is suspended above the Sun’s surface by a strong local magnetic field. (When they are viewed against the solar disk, head-on rather than off the visible edge, they are called filaments.) Prominences can erupt when the magnetic structure becomes unstable, flinging their plasma outward in a blast called a coronal mass ejection.
Solar Dynamics Observatory/NASA.
Spicules: At any given moment, as many as 10 million wild jets of solar material burst up from the Sun’s surface. Known as spicules, these grass-like tendrils of plasma erupt as fast as 60 miles per second (100 kilometers per second) and can reach lengths of 6,000 miles (9,700 kilometers) before collapsing.
