How long does it take the Sun to orbit the galaxy?

Wednesday 22nd July 2009
Submitted by Robert Matthews
Gina Hall, Bristol

We tend to think of the Sun as the stationary heart of our Solar System, with the planets orbiting serenely around it. In reality, the Sun is dragging us around the galaxy at around 800,000km/h, taking around 250 million years to complete a single orbit. That means our Solar System has made around 18 complete circuits since it was formed around 4.5 billion years ago. But they're not simple laps: the distribution of matter in the galaxy leads to the Sun and planets gently bobbing up and down, passing through the thickest parts of the galaxy's disc once every 33 million years. Some astronomers have argued that this could expose the Earth to a higher risk of being hit by galactic debris, leading to mass extinctions of life, but the evidence is far from compelling.

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