As the Earth rotates, our Moon appears to move from east to west across our sky, but its actual orbital motion is from west to east, which is why it rises later each night. In an hour, it moves about its own width eastward. You can see a graphic, and beautiful, illustration of this on the evening of Wednesday, December 3, as the moon appears to pass across the Pleiades star cluster, occulting some of its stars from our point of view.
The eastern edge of the Moon will still be in darkness, as it is not quite in its full phase, which helps make the occultations a bit more impressive to watch. You’ll want binoculars or a telescope, with a telescope giving a better view of the actual instant of disappearance, since with increased magnification you can more easily exclude the brighter areas of the Moon from the field of view.
Shown above, courtesy of SkySafari, is a view of the Pleiades, with the names of the brightest stars labeled.
Sunset for Santa Barbara will be around 4:48 PM, with the Moon already encroaching on the western edge of the star cluster. Here are the approximate times when some of the brighter members will be covered by the edge of the Moon. Allow some wiggle room so you don’t miss out, and be aware that the earliest events will be more difficult because the sky will still be bright:
Electra 4:54 PM
Celeano 5:05 PM
Maia 5:27 PM
Merope 5:33 PM
Alcyone 5:56 PM
Taygeta, Atlas, and Pleione will not be occulted from our vantage point.
The beautiful string of dimmer stars streaming southwest of Alcyone is known among amateur astronomers as Ally’s Braid. Don’t expect to see the bluish nebulosity visually.
The Pleiades are an open cluster, and as such consist of massive young hot stars, still loosely gravitationally bound and moving through space together. There are currently estimated to be about 5000 stars in the Pleiades, and they are around 400 light years away, so the light you see left those stars back when Galileo was looking at the sky.
Because of its location along the ecliptic, the yearly apparent path of our Sun, almost every culture has multiple stories associated with the Pleiades. My favorite is a Polynesian story that it was once a single star, the brightest star in the sky. It was bragging about itself all the time, so the god Tane came along with a big wooden club and broke it up into myriad stars. His problem wasn’t solved, however, as the new stars started to chatter among themselves about how much prettier they were, now that there were more of them.
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