|In this section, I'm going to tell you about the music of the Sun.|
We can hear lots of different
ringing noises in the Sun.
It's a bit like the notes and echoes you can hear in a concert hall.
The different notes are called
modes (but we shall call them waves).
They are everywhere in the Sun and
bounce around all the time.
|Here on Earth, we can hear the sounds carried by the air. We need special instruments to listen to the sound of the Sun. Here is a picture of the Sun showing 10 million musical notes.|
|You can see how the waves bounce around inside the Sun. Some modes stay near the surface. Others go all the way down to the Sun's core. The frequencies of these modes depend on the structure and dynamics of the Sun's interior. The `degree', or letter l is sometimes used instead of wavelength, and is equal to the solar circumference divided by the wavelength.|
This picture shows the difference between what we thought the speed of sound was inside the Sun and what we have measured it to be with the SOHO-MDI instrument.
The differences between the observations and theory are very small. We got it about right most of the time. The red colour means that sound travels faster than we thought. The red layer at about one third of the way down from the surface to the centre of the Sun is a shear layer just below the solar convection zone. The blue colour mean that the sound speed is lower than we expected. In the core of the Sun, the temperature may be 0.1% cooler than the expected 15 million degrees C. Although this may seem very small to you, it suggests that the power produced by nuclear fusion at present may be lower than expected, in fact that it may vary over long time periods.
Here is a beautiful image showing the differences in the speed of rotation of material in the Sun.
The colours represent speed; red material is rotating the fastest (3,000 mph), dark blue, the slowest. You can see that the material at the Sun's equator is moving faster than that near the poles.