Interesting facts - the Sun

Facts and figures

• The Sun's mass is 2 x 10²⁷ tonnes
• About 75% of the Sun is hydrogen, the rest is mostly helium.
• Gravity holds the Sun together.
• The weight of the outer layers of the Sun causes the density and temperature to increase inwards, until at the centre the temperature is 15 million degrees Celsius and the density is 160 times that of water!!
• At the centre of the Sun, hydrogen nuclei fuse into helium, releasing the energy upon which we depend.

The layers of the sun

The sun is not just a ball of gas in the sky, it is made up of different layers that all look different:

• The surface of the sun is called the photosphere and is made up of thick gases. It is called a surface, but you couldn't walk on it - you would sink into the hot gas! It looks yellowy in colour and is marked with dark splotches called sun spots. Sun spots are not there all of the time, but change from day to day.
• The photosphere is covered by two layers of atmosphere called the chromosphere and the corona. They are both almost invisible because the photosphere is so bright, and can only be seen properly with special telescopes or when there is a solar eclipse.
• The chromosphere is made up of hot gases (mainly hydrogen), that swirl around the surface of the sun. Within these gases storms can occur and even hurricanes!
• The corona is the outermost layer of the sun and stretches towards the planets as far as Mercury, getting thinner all the time.
• Under the photosphere is the interior, made up of three hot layers. The core (the central part) is the hottest, we think it is around 15,000,000 °C (remember that water boils at 100 °C and freezes at 0 °C). This is where the light we see is created by nuclear reactions between hydrogen and helium. In the next layer up, the radiative zone, the heat created in the core moves outward through the gases.
• In the convective zone, energy is transported by convection (like boiling soup). Convection therefore allows the photosphere to be heated up by the interior so that we can see the light from the sun.

Sunspots

Sunspots appear as dark spots on the surface of the Sun. Sunspots are magnetic regions on the Sun with magnetic field strengths thousands of times stronger than the Earth's magnetic field. Sunspots usually come in groups with two sets of spots. One set will have positive or north magnetic field while the other set will have negative or south magnetic field.

• Temperatures in the dark centers of sunspots drop to about 3427°C (compared to 5427°C for the surrounding photosphere).
• Sunspots usually last for several days, although very large ones may live for several weeks.
• The magnetic field in sunspots is strongest in the darkest area - the umbra. The magnetic field is weaker and more horizontal in the lighter area - the penumbra.