Dwarf planet Pluto is at opposition on 6 July at 15h UT when it will be at its ‘brightest’ (magnitude +14.1) and best placed for observation. Despite its low altitude in the constellation Sagittarius, the optimal time for viewing Pluto from the British Isles is currently around 1am BST. If you have a ‘scope of 12-inch aperture or larger, celebrate the arrival of NASA’s New Horizons spacecraft by attempting to view (or image) this enigmatic world for yourself. AN graphic by Ade Ashford.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.This wide-field Pluto finder chart showing the constellation Sagittarius is 20 degrees wide (approximately the span of an outstretched hand at arm’s length) and depicts the region of sky that lies low to the south in the British Isles around 1am BST in early July. The curved horizontal dotted lines represent parallels of declination that are five degrees apart — about the field of view of a 10×50 binocular. Stars down to magnitude +8 are shown. For detailed telescope finder charts, see below. AN graphic by Ade Ashford/Cartes du Ciel.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!This is a close-up view of the red inset box on the wide-field Pluto finder chart above, showing a quarter-degree field (half the width of the Full Moon) in considerable detail. Parallels of declination and lines of right ascension for the J2000.0 epoch are shown at 5-arcminute intervals. Pluto’s track from 7—14 July with daily positions at 1am BST are marked in red. Stars to magnitude +15 are shown, which is about one magnitude fainter than Pluto, the chart being suitable for 12-inch telescopes and larger. North is up and east is left as the chart appears in the sky; Newtonian/Dobsonian telescope users will need to invert the chart to match the eyepiece view. Click the graphic for a full-size version suitable for printing showing Pluto’s positions from 7—21 July. AN graphic by Ade Ashford/Cartes du Ciel.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!Observers with GoTo telescope mounts can locate Pluto directly by entering the topocentric J2000.0 equatorial coordinates for the date in question. For each date, right ascension and declination are computed for the centre of the British Isles at 0h UT, or 1am BST.
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.
To help mission scientists understand the diversity of Pluto’s terrain and to piece together how the dwarf planet’s surface has formed and evolved over time, NASA’s New Horizons mission scientists have started constructing geological maps. The base map for this interpretation is a mosaic of 12 images obtained by the spacecraft’s Long Range Reconnaissance Imager (LORRI).
Geologists said Thursday they are bewildered by images from NASA’s New Horizons spacecraft baring unseen landscapes on Pluto with unexpected “snakeskin” textures, colourful chasms routing through ancient landforms, and vivid new views of apparent glacial flows.
NASA’s New Horizons spacecraft took this stunning image mere minutes after closest approach on 14 July 2015. Seen here, sunlight filters through and illuminates Pluto’s complex atmospheric haze layers over portions of the nitrogen ice plains informally named Sputnik Planum, as well as mountains of the informally named Norgay Montes.
