Chance to spot the seventh planet

The moon was full yesterday, so for the next few nights, bright moonlight will wash out all but the brightest stars for most of the night.

Despite this, if weather conditions allow, it's worth staying up tomorrow, because for one night only, we can use the moon as a convenient guide to finding the planet Uranus.

When it was discovered in 1781, by the German-British astronomer William Herschel, Uranus doubled the known extent of our solar system. The planet, which is four times bigger than Earth, takes 84 years to complete one orbit at a distance of 2.8 billion kilometres from the sun. With a dim system of rings, 27 known moons, and an axial tilt of nearly 98 degrees, the planet is certainly fascinating.

Uranus is visible to the naked eye, but it was never recognised as a planet by ancient observers because of its dimness and slow orbit.

While it can be glimpsed by stargazers with keen eyesight on a clear dark night, most people need optical aid to view the seventh planet from the sun, and that's why to spot it this week you will definitely need access to a pair of binoculars.

Tomorrow night, the moon is close to Uranus in the sky. Once you see the moon, centre it in your binoculars and then slowly sweep away from the moon in the 8 o clock direction. Uranus is roughly four-degrees away (that's about 8 lunar diameters) and should be easily visibly as a distinctly blue ''star''.

Why does Uranus appear this colour? It turns out that the planet's atmosphere is composed of hydrogen, helium and methane. Methane in Uranus' upper atmosphere absorbs red light from the sun, but reflects the sun's blue light back into space. This is why Uranus appears blue when viewed from afar.

On a recent trip to the Mount John Observatory, I was able to photograph Uranus using a special filter which showed features in its atmosphere. It was fascinating to be able to study clouds in the atmosphere of a world nearly three billion km from my observatory!

-By Ian Griffin

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