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.The 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 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:
α = 06h 05m 15.0s δ = +28° 17′ 48.0″ (J2015.0)
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.If 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!
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