This finder chart for magnitude +5.4 asteroid Vesta for the period June-July 2018 is centred on a region of the constellation Sagittarius that is highest in the southern sky of Western Europe (including the UK) at 2am local time in mid-June, or by 1am local time at the end of the month. For scale, the view is 25 degrees wide, or roughly the span of an outstretched hand at arm’s length (a 10×50 binocular field is also shown on the chart). At magnitude +0.1, Saturn is the brightest object in the area. Vesta’s position is for 0h UT on the dates shown with stars down to magnitude +7. Click on the graphic for a scaleable PDF chart suitable for printing and use outside. AN illustrations by Ade Ashford.Many of you may have tracked down an asteroid – a shattered fragment of a planetesimal that never grew large enough to become a planet between the orbits of Mars and Jupiter – with binoculars or a telescope, but have you ever seen one with the naked eye? If not, then June presents you with an opportunity to see the brightest, 1 Vesta. What’s more, ringed planet Saturn happens to lie close by to act as a convenient guide.
A colour image of asteroid 4 Vesta from NASA’s Dawn spacecraft captured at a distance of about 5,200 kilometres (3,200 miles) on 24 July 2011. Some 326 miles (525 kilometres) in diameter with an orbital period of 3.63 years, Vesta is the second-largest main-belt asteroid after dwarf planet 1 Ceres. As seen from Earth, however, Vesta appears starlike in typical backyard telescopes. Image credit: NASA / JPL / MPS / DLR / IDA / Björn Jónsson.On Tuesday, 19 June, Vesta comes to opposition in the constellation of Sagittarius. At 07:50 UT on that day, the asteroid makes its closest approach to Earth for the year at a distance of 1.141568 astronomical units, or 170¾ million kilometres (106.1 million miles).
With a mean diameter of 326 miles (525 kilometres) and an orbital period of 3.63 years, potato-shaped Vesta is the second-largest main-belt asteroid after dwarf planet 1 Ceres between the orbits of Mars and Jupiter. Vesta was discovered by German astronomer Heinrich Wilhelm Olbers on 29 March 1807.
Currently shining at close to magnitude +5.6 and peaking at +5.3 at opposition, Vesta is potentially a naked-eye object for eagle-eyed observers under dark, moonless skies, particularly from the Southern Hemisphere where it is very high in the sky (the glow from a waxing Moon will interfere for roughly a fortnight from 20 June). For the rest of us with average vision, the asteroid is still an easy binocular object — if you know exactly where to look.
Where and when to see Saturn and Vesta
The ringed planet (which reaches opposition on 27 June; more on that nearer the time) and asteroid lie in a region of the constellation Sagittarius that is highest in the southern sky of Western Europe (including the UK) at 2am local time in mid-June, or by 1am local time at the end of the month. As seen from the heart of the British Isles, Saturn attains a peak altitude of just 15 degrees high in the south; Vesta transits about 1½ degrees higher.This extract of the printable PDF finder chart from the top of the page shows northwestern Sagittarius bordering on Ophiuchus with a 10×50 binocular field for scale. Stars to magnitude +7 are shown, approximately 1½ magnitudes fainter than Vesta. Celestial north is up and east is left. AN graphic by Ade Ashford.By mid-June, Vesta lies just under 8 degrees, or 1½ 10×50 binocular fields of view, to the upper right of Saturn, as seen from the Northern Hemisphere. The asteroid passes a lunar diameter (28 arcminutes, to be precise) south of magnitude +5.5 open cluster Messier 23 in the small hours of Friday, 15 June in the UK, a fine visual and astrophotographic opportunity.
Given that Vesta attains a peak altitude of just 17 degrees in the southern sky as seen from the centre of the British Isles mid-month, dimming due to atmospheric extinction amounts to around half a magnitude. Hence, Vesta will appear about magnitude +6 at best for UK observers. Southern Hemisphere observers will see both Saturn and Vesta very high in the sky, so the asteroid will appear at full brightness and a comfortable naked-eye target from moonlight-free dark sky sites.
Saturn’s clouds have roots deeper inside the planet’s atmosphere than scientists previously thought, and Saturn’s rings — now believed to have formed in the last 200 million years — appear to be raining organic molecules down on the planet, according to observations made by NASA’s Cassini spacecraft last year in the final weeks of its mission.
NASA’s Cassini spacecraft has found deep, steep-sided canyons on Saturn’s moon Titan that are flooded with liquid hydrocarbons. The finding represents the first direct evidence of the presence of liquid-filled channels on Titan, as well as the first observation of canyons hundreds of metres deep.
Mars lies highest in the sky to the south soon after sunset at the beginning of July for observers in the UK, so you should not waste any opportunities to view the Red Planet while it is close and still relatively large in size. Tharsis, the great Martian volcanic plateau that is home to the largest volcanoes in the solar system, is turned toward Earth in the first week of the month.
