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Watch the Moon eclipse the giant star Aldebaran!

Watch the Moon eclipse the giant star Aldebaran!

Last year marked the start of a series of 49 occultations of Aldebaran. Each lunar month, from 2015 to 2018, the Moon will pass in front of the V-shaped Hyades cluster in Taurus, occulting several stars along the way… and most of those months also include occultations of the bright star, Aldebaran.

Some background details

Aldebaran represents the fiery eye of Taurus the bull, and is a +0.8 magnitude orange giant that is easy to see with the naked eye, even from the city! Though it appears to be part of the V-shaped Hyades, it actually sits about 65 light years away, roughly mid way between Earth and the more distant blue stars of the “V”.

Aldebaran is also the brightest star the Moon can occult—bright enough to see on the lunar limb. Because the Moon orbits Earth at about 1 km/sec from west to east, it appears to move across the sky a distance roughly equal to its own diameter, every hour. And since the main stars of Taurus, most notably Aldebaran and the Hyades, lie along the ecliptic, they sit in the Moon’s orbital path… which means when the alignment is just right, the Moon can eclipse them. These alignments occur in cycles that are 18.6 years apart: The last Aldebaran occultation series was from 1996 to 2000; the next one will be from 2033 to 2037!

How to observe the occultation

The first of the occultations for 2016 takes place on the evening of January 19: Seen from Montreal, Aldebaran will disappear behind the waxing gibbous moon around 9:27 P.M. and will reappear on the other side about 10:43. But the exact timing is very sensitive to the observer’s precise geographical location: to avoid missing the event be prepared to begin observing a few minutes in advance. All you really need is a clear sky, and your eyes of course, though a pair of binoculars or small telescope will help reveal the colour contrast between the orange giant star and the dark limb of the gibbous moon.

Three more occultations of Aldebaran will be visible from Quebec before the end of the year: one will be underway as twilight falls on April 10; another will occur early in the evening on October 19; and the last one will take place during the night of December 12 to 13. 

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