Put your coffee pot on a timer and set your alarm for a couple of hours before sunrise on July 21. You’ll want to get up early to see the waning crescent moon, Pleiades star cluster and the red star Aldebaran adorning the early morning sky. Look east before dawn. If you get up too late, you’ll still enjoy seeing the brightest star-like object in all the heavens: the planet Venus.
The moon’s position relative to the Pleiades cluster, also know as the Seven Sisters, will be somewhat different depending on your location on the globe. These charts show how North Americans will view the waning crescent moon dawn on July 21, and closer yet to the star Aldebaran before dawn July 22.
All over the world, the moon, the Pleiades cluster and Aldebaran light up the eastern predawn sky. You should have little problem seeing the moon and Aldebaran, the brightest star in the constellation Taurus the Bull. But you may have some difficulty spotting the Pleiades cluster, especially as darkness gives way to dawn. If you have binoculars, use them. They’ll bring the Pleiades into view if you can’t see them otherwise, or will enhance your view of the Pleiades’ gossamer beauty.
If you aren’t familiar with the Pleiades, it will appear as a tiny starlit dipper. Most people see six or seven stars with the unaided eye, under good conditions. Depending on your eyesight and the local conditions, you might not even be able to see any stars in the Pleiades. Sometimes it just looks like a small glowing patch or cloud. Telescopically, there are hundreds of stars visible in the Pleiades cluster. In contrast to our sun, these stars are all significantly younger, larger and hotter. They are all about 400 light years away, and are bound to each other by gravity.
Even if you are familiar with the Pleiades, or Seven Sisters, you might think that it is just a winter delight. The Pleiades are visible in the evening in a Northern Hemisphere winter.
Yet, like all other stars, these are to be seen in the morning sky just as much as in the evening sky, even though not at the same time of year. In fact, if you know when and where to look, the Pleiades cluster is visible to some extent every night of the year from about mid-June until early the following May, when the sun comes between us and this cluster. This is not strictly true everywhere on Earth, however, because visibility of the Pleiades is more restricted in the Southern Hemisphere (it can’t be seen at all in Antarctica), and complicated in north polar regions due to long periods of daylight. For several weeks before and after May 20, the sun is located too close to the Pleiades along our line of sight for the cluster to be seen easily.
But for many of us in the Northern Hemisphere, the Pleiades cluster is a harbinger of cooler weather, since it is first seen in the early evening sky in October. So to view these Pleiades stars during the heat of July is a welcome confirmation that this season, too, shall change.