The Sun The Sun is a star. The Sun is a star. It is 4,500 million years old It is 4,500 million years old It takes 8 minutes for its light to reach the Earth. It takes 8 minutes for its light to reach the Earth. 98.6% mass of the Solar System 98.6% mass of the Solar System Consists of Hydrogen (74%) and Helium (24%) Consists of Hydrogen (74%) and Helium (24%) Radius: 695,000 km Radius: 695,000 km Mass: 333,000 Earths! Mass: 333,000 Earths! Surface Temperature: 5,500 °C Surface Temperature: 5,500 °C Core Temperature: 15,500,000 °C Core Temperature: 15,500,000 °C

Star Size Comparison

Internal Structure of the Sun Photosphere granular appearance. EM radiation emitted. Convective Zone temperature falls with increasing distance towards the surface Radiative Zone photons travel out through it Core Hottest part where hydrogen fusion occurs

Photosphere The Sun’s surface - the layer of the Sun where most of the visible light comes from. The Sun’s surface - the layer of the Sun where most of the visible light comes from. The energy released in the Sun's core takes over years to reach the photosphere. The energy released in the Sun's core takes over years to reach the photosphere.

A magnified portion of the solar surface. Energy from below the surface is transported by convection and resulting in granulation. The lighter areas reveal where gases are rising from below, while the darker areas show where cooler gases are sinking back down.

Chromosphere The 2 nd of the three main layers in the Sun's atmosphere The 2 nd of the three main layers in the Sun's atmosphere ~2,000 km deep - just above the photosphere ~2,000 km deep - just above the photosphere Normally invisible - can only be seen during a total eclipse with special equipment (the photosphere is too bright). Normally invisible - can only be seen during a total eclipse with special equipment (the photosphere is too bright). The temperature varies from ~6000K to K The temperature varies from ~6000K to K

It is not yet fully understood what causes the chromosphere to increase in temperature as you move away from the Sun

Corona The plasma "atmosphere" of the Sun The plasma "atmosphere" of the Sun Extends millions of kilometres into space Extends millions of kilometres into space Most easily seen during a total solar eclipse Most easily seen during a total solar eclipse Much hotter (nearly 200 times) than the surface of the Sun: the photosphere's average temperature is 5800K compared to the corona's 1-3 million K. Much hotter (nearly 200 times) than the surface of the Sun: the photosphere's average temperature is 5800K compared to the corona's 1-3 million K.

The solar wind is a stream of protons and electrons which flow outwards from the coronal holes.solar wind The particles get accelerated up to km/s. The solar wind particles flow through-out the solar system beyond Pluto The solar wind is a stream of protons and electrons which flow outwards from the coronal holes.solar wind The particles get accelerated up to km/s. The solar wind particles flow through-out the solar system beyond Pluto

Prominences (aka coronal loops) are large, bright loop-shaped features on the photosphere that extend out into the corona Prominences A prominence takes ~1 day to form and may persist for several months. A typical prominence extends over many 1000s of kms; the largest recorded was over kms long Prominences (aka coronal loops) are large, bright loop-shaped features on the photosphere that extend out into the corona Prominences A prominence takes ~1 day to form and may persist for several months. A typical prominence extends over many 1000s of kms; the largest recorded was over kms long

Coronal loops are found in the lower corona resulting from the Sun’s magnetic field. Coronal loops Their frequency is linked with the solar cycle. They are often found with sunspots at their footpoints. Coronal loops are found in the lower corona resulting from the Sun’s magnetic field. Coronal loops Their frequency is linked with the solar cycle. They are often found with sunspots at their footpoints.

A solar flare is a sudden brightening observed over the Sun's surfacesolar flare The frequency of solar flares varies from several per day when the Sun is "active" to less than one per week when the Sun is "quiet“. Involves a large energy release of ~160 billion megatons of TNT

Filaments are prominences viewed from above instead of side on. As they are cooler than the photosphere, they appear darker Filaments are prominences viewed from above instead of side on. As they are cooler than the photosphere, they appear darker

What are sun spots? Temporary “blemishes” on the photosphere Caused by intense magnetic activity which reduces convection, forming areas of reduced temperature (3000–4500 K). Sunspots expand and contract as they move round the Sun and can be as large as km in diameter making them clearly visible from Earth.

The Sun from the dwarf-planet Sedna

What powers a star? A star is ‘powered’ by nuclear fusion reactions in its core. Nuclear fusion involves light atomic nuclei fusing together to form heavier ones. This process releases huge amounts of energy - each second, the Sun produces 4 x joules of energy! It would take 2000 million nuclear power plants a whole year to produce the same amount of energy on Earth. A star is ‘powered’ by nuclear fusion reactions in its core. Nuclear fusion involves light atomic nuclei fusing together to form heavier ones. This process releases huge amounts of energy - each second, the Sun produces 4 x joules of energy! It would take 2000 million nuclear power plants a whole year to produce the same amount of energy on Earth.

What’s inside an atom? Inside an atom, there are three smaller things: Protons - positively charged Neutrons - neutral (no charge) Electrons - negatively charged The protons and neutrons form the nucleus in the center of the atom and this is surrounded by electrons.

Nuclear Fusion We can add neutrons to a nucleus without changing the way an element reacts. These different variations are called isotopes. Deuterium and tritium are two- and three- times as heavy as normal hydrogen.

Nuclear Fusion Inside stars, a proton (hydrogen) fuses to a neutron to make deuterium. This then fuses with another proton (hydrogen) to make helium-3.

Nuclear Fusion Once we have two helium-3 nuclei, we combine them to make helium-4 (the most common isotope of helium). Lots of energy is released at every stage of this process, in the form of light, making the Sun shine.

However, not all elements are made in the early stages of a star’s life. Some of the heavier elements are only made when a star explodes at the end of its life. Nuclear fusion in stars produces new atoms. In the early stages of a star’s life, light elements such as helium are mainly formed. When all the hydrogen has been used, other elements are fused together to make the heavier elements of the Periodic Table. How are elements made?