See the Moon glide through the Hyades and occult bright star Aldebaran

By Ade Ashford

On Wednesday, 20 January, observers in the British Isles with clear skies can see the waxing gibbous 10-day-old Moon occult first-magnitude star Aldebaran in the constellation Taurus soon after 3:20am GMT (see below for precise times). But before the main event, the Moon passes in front of other conspicuous stars in the Hyades cluster. This view is approximately five degrees high, corresponding to the field of view of a typical low-power binocular. AN graphic by Ade Ashford.
On Wednesday, 20 January, observers in the British Isles with clear skies can see the 10-day-old waxing gibbous Moon occult first-magnitude star Aldebaran in the constellation Taurus soon after 3:20am GMT (see below for precise times). But before the main event, the Moon passes in front of other conspicuous stars in the Hyades cluster. This view is approximately five degrees high, corresponding to the field of a typical low-power binocular. AN graphic by Ade Ashford.
When the Moon passes in front of a bright open star cluster, you can be assured of several stellar occultations to observe. Such is the case on the night of 19—20 January when the 10-day-old waxing gibbous Moon glides in front of the loose star cluster known as the Hyades forming the head of Taurus, culminating in the occultation of Aldebaran an hour or so before moonset for observers in the British Isles.

The first bright star to be occulted by the Moon this night is magnitude +3.8 star θ1 (theta1) Tauri. For observers in Edinburgh, the star disappears at the dark lunar limb shortly after 11:56pm GMT on Tuesday, 19 January. For Londoners, the star’s disappearance occurs some 19 minutes later.

Theta1 Tauri forms a naked-eye double star with magnitude +3.4 theta2. While the latter narrowly escapes being covered by the Moon for most of the UK, in the extreme north of Scotland it will be occulted too. As seen from Wick, for example, the star is hidden for just 14 minutes from 12:09am GMT on Wednesday, 20 January.

For those with the stamina to stay up until beyond 3am GMT — or simply wish to set their alarm for the highlight — the Moon occults magnitude +0.9 star Aldebaran a few seconds before 03:24am GMT as seen from the centre of the British Isles. As viewed from London, the star disappears behind the advancing dark lunar limb at 03:24:30 UT, or about 40 seconds earlier if observed from Edinburgh.

My advice for any budding occultation watcher is to have your telescope setup (or large binoculars steadied by leaning your elbows on a low wall or fence) at least 10 minutes before the predicted time so that you don’t miss out — plus it’s fun to see the advancing Moon glide ever closer until the star finally disappears from view. For this particular occultation of Aldebaran it is also essential to choose a location with an unobstructed view of the west-northwest as the Moon will be very low in the sky.


Inside the magazine

Find out more about this occultation of Aldebaran and what’s up in the night sky in the January 2016 edition of Astronomy Now.

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