Tomorrow before dawn – July 19, 2017 – if you’re an early riser, you might catch the waning crescent moon pairing up with the red star Aldebaran, brightest star in the constellation Tarurus the Bull. The July 19 morning moon is also in the vicinity of the Pleiades star cluster, aka the Seven Sisters, also in Taurus.
If you get up shortly before sunrise, you won’t see Aldebaran or the Pleiades in the twilight glare. But you may spot the moon and Venus, both of which are shining in front of Taurus the Bull right now. After all, the moon and Venus rate as the secnd-brightest and third-brightest celestial objects, repectively, after the sun.
Aldebaran is a bright red star, but it’s not the only bright, red star in our night sky. Aldebaran shines virtually opposite (180o) of the red supergiant star Antares, the bright, red star in the constellation Scorpius the Scorpion. Antares is sometimes called the Scorpion’s Heart. Because they’re opposite each other on the dome of sky, you won’t see Aldebaran and Antares in the same sky together. For example, Aldebaran won’t be visible this evening. Meanwhile, Aldebaran’s counterpart star – Antares – pops into view as soon as darkness falls.
Incidentally, in 2017, the golden planet Saturn shines in the vicinity of Antares, as seen from around the world.
So the red star Antares – the star near Mars and Saturn now – and the red star Aldebaran lie opposite one another on the great sphere of stars. In both the Northern and Southern Hemispheres, look for Antares and the planet Saturn as night begins. Look south from the Northern Hemisphere. From the Southern Hemisphere, look northeast at nightfall – overhead around 9-10 p.m. That’s 9-10 p.m. local time, the time on your clock no matter where you are on the globe.
Antares and Saturn will drift westward throughout the night. After they set, look for the waning crescent moon and star Aldebaran to rise on July 19.
With each successive day, Antares sets four minutes earlier, while Aldebaran rises four minutes earlier. Or, with each successive month, Antares sets two hours earlier, while Aldebaran rises two hours earlier.
So, as the days and weeks roll by, Antares spends less time in the evening sky after sunset while Aldebaran spends more in the morning sky before sunrise.
When December finally arrives, Aldebaran will be out all night long, and Antares will be lost in the sun’s glare.
We in the Northern Hemisphere associate Antares with the hot season because we see this star on summer evenings. And in winter, we associate Aldebaran with the cold season because we see this star on winter evenings.
In the Southern Hemisphere, the opposite is true. Antares is a winter star. Aldebaran is a summer star.
Bottom line: The moon is waning in the predawn sky. It’s close to the star Aldebaran and the Pleiades star cluster, before dawn on July 19.