By Preeti Singh
Our Sun is a yellow dwarf star, a hot ball of glowing gases at the heart of our solar system. Its gravity holds the solar system together, keeping everything – from the biggest planets to the smallest particles of debris – in its orbit. The connection and interactions between the Sun and Earth drive the seasons, ocean currents, weather, climate, radiation belts, and auroras. Though it is special to us, there are billions of stars like our Sun scattered across the Milky Way galaxy.
Size and Distance
With a radius of 432,168.6 miles (695,508 kilometres), our Sun is not an especially large star – many are several times bigger – but it is still far more massive than our home planet: It would take 332,946 Earths to match the mass of the Sun. The Sun’s volume would need 1.3 million Earths to fill it.
Earth and the Sun
The Sun is about 93 million miles (150 million kilometres) from Earth. Its nearest stellar neighbour is the Alpha Centauri triple star system: Proxima Centauri is 4.24 light-years away, and Alpha Centauri A and B – two stars orbiting each other – are 4.37 light-years away. (A light-year is the distance light travels in one year, which is equal to 5,878,499,810,000 miles or 9,460,528,400,000 kilometres.)
Structure
The Sun, like others stars, is a ball of gas. In terms of the number of atoms, it is made of 91.0% hydrogen and 8.9% helium. By mass, the Sun is about 70.6% hydrogen and 27.4% helium.
The Sun has six regions: The core, the radiative zone, and the convective zone in the interior; the visible surface, called the photosphere; the chromosphere; and the outermost region, the corona.
At the core, the temperature is about 27 million degrees Fahrenheit (15 million degrees Celsius), which is sufficient to sustain thermonuclear fusion. This is a process in which atoms combine to form larger atoms and in the process release staggering amounts of energy. Specifically, in the Sun’s core, hydrogen atoms fuse to make helium.
The energy produced in the core powers the Sun and produces all the heat and light the Sun emits. Energy from the core is carried outward by radiation, which bounces around the radiative zone, taking about 170,000 years to get from the core to the top of the convective zone. The temperature drops below 3.5 million degrees Fahrenheit (2 million degrees Celsius) in the convective zone, where large bubbles of hot plasma (a soup of ionized atoms) move upwards.
Orbit and Rotation
The Sun, and everything that orbits it, is located in the Milky Way galaxy. More specifically, our Sun is in a spiral arm called the Orion Spur that extends outward from the Sagittarius arm. From there, the Sun orbits the centre of the Milky Way galaxy, bringing the planets, asteroids, comets, and other objects along with it. Our solar system is moving at an average velocity of 450,000 miles per hour (720,000 kilometres per hour). But even at this speed, it takes us about 230 million years to make one complete orbit around the Milky Way.
Surface
The surface of the Sun, the photosphere, is a 300-mile-thick (500-kilometer-thick) region, from which most of the Sun’s radiation escapes outward. This is not a solid surface like the surfaces of planets. Instead, this is the outer layer of the gassy star.
We see radiation from the photosphere as sunlight when it reaches Earth about eight minutes after it leaves the Sun. The temperature of the photosphere is about 10,000 degrees Fahrenheit (5,500 degrees Celsius).
Atmosphere
Above the Sun’s photosphere are the tenuous chromosphere and the corona (crown), which make up the thin solar atmosphere. This is where we see features such as sunspots and solar flares.
Visible light from these top regions is usually too weak to be seen against the brighter photosphere, but during total solar eclipses, when the Moon covers the photosphere, the chromosphere looks like a red rim around the Sun, while the corona forms a beautiful white crown with plasma streamers narrowing outward, forming shapes that look like flower petals.
Magnetosphere
The electric currents in the Sun generate a complex magnetic field that extends out into space to form the interplanetary magnetic field. The volume of space controlled by the Sun’s magnetic field is called the heliosphere.
The Sun’s magnetic field is carried out through the solar system by the solar wind – a stream of electrically charged gas blowing outward from the Sun in all directions. Since the Sun rotates, the magnetic field spins out into a large rotating spiral, known as the Parker spiral.
The Sun doesn’t behave the same way all the time. It goes through phases called the solar cycle. Approximately every 11 years, the Sun’s geographic poles change their magnetic polarity. When this happens, the Sun’s photosphere, chromosphere, and corona undergo changes from quiet and calm to violently active. The height of the Sun’s activity, known as solar maximum, is a time of solar storms:
