As September draws to a close on Sept. 30, an 80% illuminated waning gibbous moon pays a visit to the iconic Pleiades (M45) open cluster. While this stellar nursery is normally a dazzling, easy sight through binoculars, tonight's viewing dynamic presents a unique and dramatic observation challenge. The intense lunar spotlight casts significant glare across the cluster, heavily washing out its faint blue reflection nebulosity.
The close encounter also makes the Pleiades particularly easy to locate. Simply find the bright moon and look nearby for the compact gathering of stars. The cluster is bright enough to see with the naked eye from a reasonably dark location, though binoculars will reveal many more of its stars.
Use this intense phase contrast as a fun visual challenge. Take a moment to look closely at the cluster and try to memorize or name its most prominent members: Alcyone, Maia, Electra, Taygeta, Merope, Asterope, and Celaeno, alongside their mythological parents Atlas and Pleione. See how many of these seven sisters you can consciously pick out before the lunar glare overwhelms your night vision.
You can also try using averted vision to tease out some of the fainter stars. Instead of looking directly at your target, look slightly to one side of it. This places the light on a more sensitive part of your retina and can make faint objects easier to see.
If the gibbous moon becomes too overwhelmingly bright, use a simple field trick: position yourself so the edge of a house, a chimney, or a thick tree branch completely blocks the lunar disk from view, allowing you to observe the sparkling cluster in relative darkness.
If you are setting up a camera, try capturing a wide-field time-lapse sequence over several hours. Watching the moon's rapid orbital motion physically carry it across the sky relative to the fixed, glittering background stars of the Pleiades makes for a mesmerizing astronomical animation.
