The Sun

It is the centre of our solar system and the nearest star to Earth. Our Sun is essential to all life on our planet.

Our Sun is just one star of about 100 billion stars in our galaxy, the Milky Way. It orbits about 25,000 light years (the unit used to measure distances in space, which equals about 10,000,000,000,000 km) from the galactic core. It takes the Sun about 250 million years to complete one full revolution.

Containing about 98% of the mass of the solar system, the Sun sits 149.6 million kilometres from Earth (also known as 1 Astronomical Unit or 1 AU, the unit by which we measure distances in our solar system). It prevents us from succumbing to the absolute cold of space and gives us life, weather and ocean currents. Though not large by star standards, one hundred Earths could span the Sun and one million Earths could fit inside the blazing star. It takes eight minutes for the Sun’s light to reach Earth.

There are six distinct regions on the Sun. In the interior, there is the core, the radiative zone, and the convective zone. There is also the visible surface (the photosphere); the chromosphere; and the outermost region, called the corona. The Sun’s core is hot – about 15 million degrees Celsius. That is where its thermonuclear fusion takes place, powering the Sun, giving us heat and light. At the surface – the photosphere – the temperature is much cooler, around 5,500 degrees Celsius.

What makes it especially interesting to us here on Earth, however, is the Sun’s solar cycle. Every 11 years the Sun goes through a solar maximum. During that time, dark sunspots pepper the sun’s surface. How is this important to us? There are several reasons, one of which is solar flares. These flares are massive bursts of energy that can be directed at Earth, reaching us within mere minutes. Another is a coronal mass ejection (CME). These are huge gas bubbles which have magnetic field lines which are then ejected from the corona into space. CMEs disrupt the solar wind and can hit Earth. These can disrupt our way of life, possibly disabling satellites, endangering astronauts or knocking out electrical systems as it did in Québec in 1989. Although the Sun’s corona was known about for thousands of years (during eclipses it is briefly visible), CMEs were only discovered during the space age.

Our Sun won’t last forever, though we’ll never see its demise: it will take another 5 billion years for it to exhaust its fuel. When it does meet its end, it will swell, enveloping Earth and beyond and then shed its outer layers, becoming a white dwarf. Not out with a bang, but with a sigh.