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, 4 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 moon Dione received a fleeting visitor on 16 June, when NASA’s Cassini spacecraft whizzed by to image bizarre streaks thought to be canyons with ice walls up to 100 stories tall.
Have you ever seen a dwarf planet? Of the five within our solar system recognised by the International Astronomical Union – Ceres, Pluto, Haumea, Makemake and Eris – only Ceres can be considered bright and easy to locate. It reaches opposition in the constellation of Scorpius on 29 May at magnitude +7, an easy binocular object if you follow our guide.
In the small UK hours of Sunday 14 May, the rising 17-day-old Moon in the southeast lies just 2.4 degrees to the upper-left of Saturn, meaning that the pair will comfortably fit in the same field of view of a typical 10×50 binocular. The ringed planet is now about a month from opposition, so now’s the time to hone your observing skills.
