Watch asteroid (4) Vesta hide a naked-eye star in Aries on 11 February

By Ade Ashford

Second-largest asteroid (4) Vesta currently shines at around magnitude +8, a comfortable binocular object as it traverses southeastern Aries at a rate of about ½° per day. Vesta passes in front of magnitude +5.3 star HIP 14439 close to 10:02pm GMT (22:02 UT) on Tuesday, 11 February 2020 as seen from the north of England, Northern Ireland and Scotland. Click on the graphic for a downloadable PDF version of this chart suitable for printing. AN illustration by Ade Ashford.
The asteroid belt that lies between the orbits of planets Mars and Jupiter is believed to contain between 1 million and 2 million lumps of rock larger than 1 kilometre in diameter, with millions more smaller bodies. Despite these vast numbers, however, the sight of a minor planet occulting (passing in front of) a bright naked-eye star is still a rare occurrence.

An occultation of Regulus in Leo by the 73-kilometre-wide asteroid (163) Erigone happened on 20 March 2014 across a track that included New York City, but clouds prevented anyone in New York State or Ontario seeing the star hidden for up to 14 seconds. Similarly, the dimming of brightest star Sirius by five-km-wide (4388) Jürgenstock on 19 February 2019 went unobserved from Central America, southern Chile and Argentina.

Astronomers have their fingers crossed that clear skies will prevail for the occultation of magnitude +5.3 star HIP 14439 in the constellation of Aries by asteroid (4) Vesta on 11 February 2020. The event occurs around sunset for observers on the US Eastern Seaboard and Nova Scotia, but happens in a dark sky close to 10:02pm GMT (22:02 UT) as seen from the north of England, Northern Ireland and Scotland.

Where to see the occultation in the British Isles

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. A potato-shaped body measuring 573 × 557 × 446 kilometres with an orbital period of 3.63 years, Vesta is the second-largest main-belt asteroid after dwarf planet (1) Ceres. Image credit: NASA / JPL / MPS / DLR / IDA / Björn Jónsson.
HIP 14439 and Vesta lie about 27 degrees high in the west-southwest for skywatchers in the British Isles, where the predicted southern limit of the track is a line drawn from Newport in County Mayo, Ireland, through the Isle of Man to Scarborough in North Yorkshire. The northern limit encompasses all of Scotland with the exception of the Shetland Islands. For a graphical representation, see the map at the bottom of this page.

Vesta is a potato-shaped body with a mean diameter of 525 kilometres, hence its projected ‘shadow’ track over the north of England, Northern Ireland and Scotland is an ellipse that makes its predicted landfall in the west close to 22:01:45 UT to around 22:02:07 UT in the east. The occultation will last a maximum of 28 seconds, but considerably shorter if you happen to lie close to the edge of the track.

The glow from a rising 17-day-old waning gibbous Moon low in the east-southeast as seen from the UK at 10pm GMT on 11 February means that magnitude +5.3, HIP 14439 is a borderline naked-eye object. However, both Vesta and the star are comfortable binocular targets if you use the finder chart at the top of the page (or click here to download the PDF version). You can also look for planet Uranus while in the vicinity!

Viewing an appulse
Even if you happen to lie outside the occultation zone, it will be entertaining to watch Vesta’s close approach (or appulse, to use the correct terminology) to HIP 14439. The asteroid passes just north of the star close to 10:02pm GMT (22:02 UT) as seen from the Republic of Ireland, Wales and most of England.

At the time of closest approach, the star and asteroid will be just a fraction of an arcsecond apart as viewed from London, unlikely to be resolved. How long do they appear merged at high magnification in your telescope? Observers using instruments with GoTo mounts can use the following J2000 coordinates for HIP 14439: α = 03h 06.4m, δ = +13° 11′. (JNow: α = 03h 07.5m, δ = +13° 16′.)

Based on the latest predictions, the observability track for the occultation of magnitude +5.3 star HIP 14439 by (4) Vesta as seen from the British Isles is shown on this map. For anyone viewing from within the orange band, a three-magnitude drop in brightness to that of the asteroid should start at 22:01:45 UT (in the west of the UK) to 22:02:07 UT (in the east) and last a maximum of 28 seconds, but considerably less if you happen to lie close to the edge of the track. AN graphic by Ade Ashford/OpenStreetMap.