The Sun

Structure

10.2 - Know the location and relative temperatures of the Sun’s internal divisions, including:
a - core
b - radiative zone
c - convective zone
d - photosphere

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10.3 - Understand the role of the Sun’s internal divisions in terms of energy production and transfer

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10.5 - Know the location, temperature and relative density of components of the solar atmosphere, including:
a - chromosphere
b - corona

Internal Divisions

Core
Temperatures reach over 15,000,000°K at the core where the Sun produces its energy.

Radiative and Convection Zones
Light and heat move through these regions of the Sun, temperatures range from 2,000,000°K to 6,000°K.

Photosphere (Sphere of light)
This is the surface layer of the Sun that we are able to see. Average temperatures are approximately 5,800°K. Features of the photosphere include a process called granulation. These are circular areas with a thin darker area around them. Sunspots are visible in the photosphere.

External Layers

Chromosphere (Sphere of colour)
The chromosphere extends for thousands of kilometres above the photosphere, although is relatively thin when we consider the size of the Sun. The chromosphere can only be very briefly observed at the time of a solar eclipse and then only at the beginning and end of one when observers can detect a thin pink rim around the Sun.

Corona
The corona is the outmost part of the Sun's atmosphere. It consists of gases that are expelled from the Sun. We can observe it best during a solar eclipse when the Moon blocks out the photosphere and chromosphere of the Sun. It then appears as a 'halo' surrounding the Sun. It can also be seen using special equipment called a coronagraph.

The corona stretches millions of kilometres from the chromosphere and temperatures may reach 2,000,000°K. The Corona does not generate heat as such; the high velocity of particles within it is the result of the temperature thought to be due to magnetic fields.

High velocity solar particles interact with the magnetic field of the Sun. Some particles are pulled back towards the Sun while others are so energised that they flow outwards from the corona at high speeds to form the Solar Wind. The corona also emits X-rays.