This is the second part of the lecture given by Astronomer Royal Martin Rees at Stephen Hawking's birthday symposium.

What happens when magnetic fields get tangled up in knots? This does happen in the Sun's atmosphere and mathematical models predict that once the magnetic field becomes tangled, it must retain some vestige of this complexity for a long time. This enables the storage of vast quantities of energy. In this article I will outline how the notion of magnetic topology helps us to understand the physical situation and draw such conclusions.

Experiment discovers evidence for dark matter
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The obvious answer is 24 hours, but, as Nicholas Mee discovers, that would be far too simple. In fact, the length of a day varies throughout the year. If you plot the position of the Sun in the sky at the same time every day, you get a strange figure of eight which has provided one artist with a source for inspiration.
And what are gravitational waves?
Find out with Martin Rees
Scientists crack black holes' balancing act
Sophie Butchart finds mysterious patterns in the solar system
Adding weight helps Earth dodge killer asteroids