The Sun is an ordinary star but the center of everything in our solar system. Its gravity holds the planets in orbit, its light and heat make life on Earth possible, and its activity affects space all the way to the edge of the heliosphere.
Gravity: the anchor
The Sun contains about 99.8 percent of the mass of the solar system. Its gravity keeps the eight planets, dwarf planets, asteroids and comets in orbit, out to the distant Oort Cloud. See how astronomers study the dynamics of the solar system.
Energy: light and heat
In its core, at about 15 million kelvin, the Sun fuses hydrogen into helium, converting about 4 million tons of matter into energy every second. This energy takes a very long time, perhaps tens of thousands of years or more, to work its way out to the surface, then about 8 minutes and 20 seconds to reach Earth as sunlight.
On Earth, sunlight:
- drives photosynthesis and almost all food chains,
- powers weather, ocean currents and the water cycle,
- sets the seasons through Earth’s tilted axis,
- defines the habitable zone, the range of distances where liquid water can exist on a planet’s surface, see Earth-like planets.
The solar wind and the heliosphere
The Sun constantly blows a stream of charged particles, the solar wind, into space. It carries the Sun’s magnetic field and inflates a vast bubble, the heliosphere, which shields the solar system from part of the galactic cosmic rays, see where cosmic rays come from. Voyager 1 crossed its boundary in 2012.
Space weather
The Sun follows an activity cycle of about 11 years. Around solar maximum, sunspots, solar flares and coronal mass ejections are more frequent. These can disrupt radio, GPS, satellites and power grids, and create auroras, see solar flares.
What it is made of and how old it is
The Sun is about 73 percent hydrogen and 25 percent helium by mass, with traces of heavier elements, known from its spectrum, see what starlight reveals. It formed about 4.6 billion years ago, along with the rest of the solar system.
The Sun’s future
The Sun is halfway through its main-sequence life. It is slowly brightening, and in about a billion years it will be hot enough to evaporate Earth’s oceans. In about 5 billion years, it will swell into a red giant and then become a white dwarf, see how stars evolve.
Never look directly at the Sun, and never through binoculars or a telescope without a proper certified solar filter: it causes permanent eye damage.
