This looping animation shows a simulated 5-degree-wide 10× binocular view of the waning lunar crescent’s passage through the Hyades open star cluster in Taurus on the morning of Saturday, 24 August 2019 as seen from the heart of the British Isles. The 22-day-old Moon’s position is shown at 15-minute intervals from 3:30am BST to slightly after sunrise. Naked-eye stars delta1 (δ1), δ2 and δ3 are magnitudes +3.8, +4.8 and +4.3, respectively. The article below gives precise timings of the disappearance and reappearance of these stars for locations in the UK. AN animation by Ade Ashford.The Hyades in the constellation of Taurus is the closest open star cluster to the Solar System at an average distance of about 150 light-years. It contains hundreds of stars that lie within a 10 light-year radius that are around 625 million years old.
On Saturday, 24 August 2019 between the onset of astronomical twilight and slightly after sunrise, observers in the UK can observe the 22-day-old waning crescent Moon occult (or hide) three naked-eye Hyadean stars. They are delta1 (δ1), δ2 and δ3 Tauri which are magnitudes +3.8, +4.8 and +4.3, respectively.
While the animation shown above depicts a binocular user’s perspective to give an overview of the Hyades, only the reappearances of δ1 and δ2 Tauri at the darkened limb (edge) of the Moon will be clearly seen with such modest optical aid. The disappearances of all three stars at the bright lunar limb requires a small telescope at a magnification of around 50×, as will the reappearance of δ3 Tauri.
The table below gives the British Summer Times (BST) of the disappearance and reappearance of each star for three locations in the UK. Note that sunrise occurs close to 6am BST on this day for most of the British Isles, so the final reappearance of δ3 Tauri will occur in daylight. Telescope users with computerised GoTo mounts can use the current epoch coordinates listed in the table to be sure of identifying the star, even in a bright sky.Computation and AN graphic: Ade Ashford.As with all occultation observations, to avoid missing out make sure that you are ready at the eyepiece of your telescope a few minutes before the appointed times of the location nearest you. The Moon’s eastward motion against the stars is never more evident than when an occultation is about to occur, but what is more spectacular is a bright star’s almost instantaneous reappearance at the Moon’s dark limb – as in these morning events on 24 August 2019.
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