Page 16 - Curriculum Visions Dynamic Book

The Sun’s gravity
The Sun’s gravitational field is so strong that there is a great tendency for the Sun to collapse in on itself. That does not happen because of the huge pressure exerted against gravity by the burning atoms in the core, which always want to expand.
It is believed that the gases at the center of the Sun are squashed to a density six times as great as the atoms in the core of the Earth and exert an outward pressure that is ten thousand times as strong as the atoms in the center of the Earth.
The gases in the core behave as though they were a solid body, although they are still a gas. The core, the inner 25% of the Sun’s radius, has a pressure of 250 billion Earth atmospheres.
Modeling the Sun
How is it that we know anything at all about the inside of the Sun? In part, this is entirely theory, with scientists making up models in which they assume the Sun has certain properties, and then testing the model on a computer to see if it behaves as the Sun does. If it does not, they tweak the data and try again.
But knowledge of the Sun is also obtained in
the same kind of way we find out about the deep regions of the Earth—just by listening to the way the surface vibrates and studying the pattern of vibrations. On Earth the vibrations are either set up by explosions or by earthquakes. In the case of the Sun information has been gathered about the way its surface shakes (see page 32). This study is called helioseismology.
Scientists can also find out a great deal about the composition of the Sun by looking at the light it gives out. Every element, such as sodium and calcium, burns with a unique colour. You see this, for example, when a piece of calcium is burned
in a flame.
 This picture is a combination of images obtained by looking at the radiation the Sun emits in different wavelengths of uLtravioLet light. The result shows features that we could not see in visible light.
Notice the pLasma being released from the surface and following curved lines. These flows are controlled by the maGnetism of the Sun. Differences in brightness on the surface show where energy is reaching it more effectively in some places than in others.
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