Launched on 19 January 2006, NASA’s New Horizons spacecraft has spent the last nine years and five months crossing 3 billion miles of the Solar System at high speed, en route to a close encounter with dwarf planet Pluto and its family of five moons on 14 July 2015. Travelling at 32,500 miles per hour (14.5 kilometres per second), there is no way that the spacecraft can slow down or enter into orbit around Pluto to conduct a long-term study — this is a one-time encounter and all of New Horizons’ key mission objectives must be accomplished in the fleeting precious hours it will lie within the Pluto system.
Just 1473 miles (2370 kilometres) in diameter — one fifth of the size of our planet — and currently 2,964 million miles from Earth, perhaps its not surprising that Pluto is a challenge to observe as it looks just like a faint star, but one that moves against the real stellar background from night to night. At magnitude +14, it requires a telescope of around 12-inch aperture to see visually, but it can be photographed with instruments of much smaller aperture. Pluto is at opposition, closest and brightest for 2015, on 6 July. If you have a large ‘scope, why not take the Pluto Challenge and attempt to locate this remarkable object over the next two weeks when the Moon is out of the sky? Tip: use our Almanac to obtain lunar rise/set and twilight times wherever you may live in the world.It has to be said that Pluto’s current location in the constellation Sagittarius and southerly declination of -20.7° means that it is a difficult object for observers in the UK, especially with the residual twilight all night. From the centre of the British Isles, Pluto will attain a peak altitude of just 15 degrees above the southern horizon around 1am BST. So the further south you live, the better your chances of seeing it will be. If you really wish to feel envious of the optimal views Southern Hemisphere observers are currently enjoying, Pluto lies within 15 degrees of the zenith when on the meridian as seen from Sydney, Australia!From 9 July the waning old crescent Moon will not be above the horizon at the time Pluto is on the UK meridian, and by the time of the New Horizons encounter with the dwarf planet on 14 July we will be approaching New Moon, so start planning your Pluto party now and pray that skies remain clear!
Inside the magazine
You can find out more about observing Pluto in the July edition of Astronomy Now in addition to a full observing guide to the night sky.
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