2016 January 10

Rare asteroid occultation visible from UK on Sunday, January 17

Richard Miles

The large (210km) asteroid (41) Daphne will occult a 9th magnitude star in the constellation of Taurus on the evening of Sunday, January 17. The event is extremely favourable, even more so than last September’s stellar occultation by asteroid (275) Sapientia, which proved to be the best-observed event of its kind ever seen from the United Kingdom. The body of the asteroid will block out the light from the star for an unusually long time – up to a maximum of ~26 seconds for an observer situated near the centre of the shadow track. The map shows the expected track of the asteroid’s shadow cast by the star as it crosses France and the UK. The track shown is based on the latest (Jan 6) prediction by Steve Preston.

As you can see the shadow, which when projected onto the UK spans more than 300 km in width, will track across >95% of the country in about 90 seconds. Depending on your viewing location, the star in question will be situated at an altitude of 30-40 deg towards the south-west, whilst a 61% illuminated Moon will be some 25 deg distant.

N.B. Asteroid (41) Daphne also has a tiny moon some 2 km or less across and so this too may occult the star in a separate event lasting ~0.25 second or less shortly before or after the main event.

UK-based observers should watch or video record the 9.7 magnitude star (TYC 0075-00715-1, RA 04h 26m 25.88s. DEC +01° 40′ 43″) at 22:42‒22:47 UT. If possible try and measure the exact times the star disappears and re-appears. When occulted, only the reflected light from the asteroid will be visible, which will be nearly magnitude 13. Detailed observing advice and finder charts are available on the webpage maintained by the BAA’s occultation co-ordinator, Tim Haymes. Tim will be pleased to receive observational reports and timings (tvh.observatory [at] btinternet.com).