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

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.

Comments: 2

"... passing through the

Wed, 2011-06-22 07:48
KingPhillip

"... passing through the thickest parts of the galaxy's disc once every 33 million years."

The above quoted line suggests parts of our galaxy are stationary(!) or our solar system is moving faster orbitally than the spirals such that we traverse eight spirals in one revolution around the galactic center.

Not stationary

Thu, 2011-06-23 00:29
Shadowwolf

I don't think any part of the galaxy is stationary, nor are we going so fast that we pass from spiral arm to spiral arm. Just that our movement relative to the galactic plane is not a straight line always parallel to that plane. Hence as it all moves about the galactic center Sol also bobs up and down essentially and thus passes through the thicker regions of the plane from time to time.

It helps to think of Sol's orbital path as not being akin to the orbit of a planet about Sol as there are many more variables in play.

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