According to present estimates, there are approximately 2 million asteroids larger than 1 kilometre in size within the main asteroid belt between the orbits of Mars and Jupiter. Of those, approximately 5000 may be 20 kilometres (12 miles) in diameter — the diameter of asteroid 1630 Milet, for instance, which was discovered in 1952 and orbits the Sun every 5¼ years.12-mile-wide asteroid 1630 Milet has a 5.27-year orbit some 3 Astronomical Units from the Sun. Click the graphic to open an interactive orbit Java applet. Image credit: NASA JPL Small-Body Database Browser/Osamu Ajiki/Ron Baalke/Ade AshfordThe vast majority of these minor planets are too faint to be detected visually even with large backyard telescopes, but they still make their presence known when they pass in front of a star, an event known as an occultation. If the occulted star happens to be bright then the effect is quite dramatic, as the light dims to that of the asteroid, only for the star to return to normal brightness the instant the minor planet’s orbital motion carries it out of the way. Typically, the occulted star’s light is extinguished for only a few seconds.
On Sunday, January 11th, 15th-magnitude 1630 Milet occults HIP 28748 as seen from the British Isles close to 9:05 pm GMT. The star lies in southern Auriga on the border with Gemini and Taurus and has a visual magnitude of +8.1, making it a viable target for small telescopes or large binoculars.
The occultation track cuts a swathe across China, Kazakhstan, Russia, Belarus, Poland, Germany and the Netherlands before making landfall in the UK near Aldburgh on the Suffolk coast about 21:04:40 UT (9:04:40 pm GMT). The projected UK ground track of 15th-magnitude asteroid 1630 Milet’s occultation of 8th-magnitude star HIP 28748 on January 11th. The black line is the predicted centre line of the track that makes landfall on the Suffolk coast close to 21:04:40 UT (9:04:40 pm GMT) and leaves the Welsh coast near Swansea around 21:05:25 UT. The parallel blue lines show the predicted zone where HIP 28748 could be seen to ‘vanish’ for a couple of seconds as the asteroid blocks its light. The red lines show the extreme northern and southern limits based on orbital prediction uncertainties. Observers within the red zone are therefore encouraged to monitor the star visually or by astrovideo between 21:04 and 21:06 UT. Click the graphic for an interactive Google map. Image credit: Google/Geoff Hitchcox/Steve Preston.
The finder chart below will help you locate HIP 28748, given that the star will lie approximately 60° above the southeast horizon in the UK at the time of the event. If you have a telescope on a GoTo mount, you can find it directly from the following coordinates:
Binocular observers will find it easiest to locate magnitude +1.6 β Tauri on the border of Taurus and Auriga and star hop 8.5° (~ two binocular fields) due east at almost the same declination in the direction of Pollux in Gemini.Detailed finder chart for 8th-magnitude star HIP 28748 in southern Auriga, the star to be occulted by 15th-magnitude asteroid 1630 Milet on 11th January. At the time of the event (~21:04—21:06 UT), HIP 28748 will lie nearly 60° above the southeast horizon in the British Isles. Click on the graphic for a full size B/W chart suitable for printing. AN graphic by Ade AshfordIf you find yourself near the centreline of the occultation track, the star will wink out for a couple of seconds before returning to its normal brightness. Observers with astrovideo equipment and accurate timing facilities are encouraged to monitor the star from 21:04—21:06 UT, not only for the main event, but for any brief secondary occultation that may indicate the presence of a tiny moon for 1630 Milet. Clear skies!
The orbits of Jupiter’s large Galilean moons Io, Europa, Ganymede and Callisto are presently almost edge-on to our line of sight, causing the moons to regularly eclipse and occult each other. Multiple shadow transits are also on view!
The last lunar occultation of a conspicuous naked-eye star for UK observers in 2014 occurs around 6 am on Tuesday, 9th December. Set your alarm and prepare your telescope for the disappearance and reapparance of λ Geminorum.
For those in the west of the British Isles, magnitude-4.2 star θ Aquarii slips behind the darkened limb of the 2-day-old Moon soon after 7:15 pm — an event visible in binoculars.
