The Sun, a yellow dwarf star, is the glowing heart of our solar system. Its gravity anchors everything from the largest planets to the smallest debris.
As a yellow dwarf star, the Sun is a sphere of superheated gas powering our solar system. Its gravity
binds the system together.
The Sun drives Earth's seasons, weather, and climate. Though typical among billions of stars in the
Milky Way, it is the sole source of light and life for our planet.
Its Latin name "Sol" gives us the term "solar."
With a radius of 432,168 miles (695,508 kilometers), the Sun is massive compared to Earth—it would take
1.3 million Earths to fill it.
Located 93 million miles (150 million kilometers) away, it is our closest star. The next nearest,
Proxima Centauri, is 4.24 light-years distant.
The Sun and the solar system reside in the Milky Way's Orion Spur. Orbiting the galactic center at
450,000 mph (720,000 kph), it takes about 230 million years to complete one circuit.
The Sun rotates as it orbits, with an axial tilt of 7.25 degrees. Because it is gaseous, it rotates
differentially: the equator spins once every 25 days, while the poles take 36 days.
The Sun formed 4.5 billion years ago from the collapse of a solar nebula. The vast majority of the
nebula's material (99.8%) gathered to form the Sun.
Currently a main-sequence star, the Sun has enough fuel for another 6.5 billion years before it evolves
into a red giant and eventually a white dwarf.
The Sun is a ball of plasma, composed mainly of hydrogen (91.0% by atoms, 70.6% by mass) and helium (8.9% by atoms, 27.4% by mass).
Gravity generates immense pressure and heat at the core, reaching 27 million degrees Fahrenheit (15
million degrees Celsius), triggering nuclear fusion where hydrogen becomes helium.
This energy radiates outward through the radiative zone (taking 170,000 years) and then convects to the
surface. The visible surface (photosphere) is cooler, at about 10,000°F (5,500°C), but still hot enough
to boil carbon.
Internal Structure of the Sun
The photosphere is the 300-mile-thick visible "surface" from which sunlight escapes. It is not solid but a layer of gas at roughly 10,000°F (5,500°C). Sunlight reaches Earth about eight minutes after leaving this layer.
Above the photosphere are the chromosphere and the corona. These rarified layers are the site of sunspots
and flares.
During an eclipse, the corona appears as a pearly white halo. Strangely, the atmosphere gets hotter with
altitude, reaching millions of degrees—a long-standing mystery.
While the Sun itself is too hot to sustain life, its energy is the foundation for almost all life on Earth.
The Sun and other stars don't have moons; instead, they have planets and their moons, along with asteroids, comets, and other objects.
The Sun does not have rings.
The Sun generates a magnetic field that envelops the solar system in a "heliosphere."
Solar wind—electric currents of gas—carries this field outward, spiraling as the Sun rotates.
Every 11 years, the Sun's magnetic poles flip, marking the peak of solar activity (solar maximum). This
period sees increased sunspots, flares, and coronal mass ejections, which can cause space weather
effects on Earth.