The Pleiades are recognised by countless cultures around the world, almost always as a group of sisters. In Greek mythology, they were the daughters of Atlas and Pleione. The hunter Orion spotted them in the countryside and, taking a fancy to them, gave chase. For seven years they tried to avoid him until Zeus answered their prayers by turning them into doves and placing them in the sky out of Orion’s reach.
Presumably the chase continues, because they regularly hide behind the moon in an occultation like the one we’ll see in South Africa this Sunday (21 February)!
This will be very easy to see as you just have to find the Moon, and the rather obvious cluster (only slightly larger) passing behind it- the Moon moves slowly enough that show will last almost from sunset till the moon sets at about 10:30 pm. An occultation occurs whenever one body passes in front of another (from the Latin Occultus, meaning ‘hidden’, ‘concealed’, or ‘secret’).
Until recently, astronomers used events such as this to determine the finer details of the Moon’s orbit. They relied on the fact that the exact position of the Moon, relative to the stars, varies considerably according to your location on the surface of the earth. By recording the precise times at which specific stars were blotted out from various viewpoints around the country, they could calculate the Moon’s position with remarkable accuracy. Today, such experiments are often repeated by amateur astronomers, both for the fun of repeating the work of great scientists through history, and as a valuable service to observatories world-wide. Amateur observations are routinely used as a supplement to professional data! If you’re interested in joining similar efforts, contact your local Astronomical Society.
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