Tomorrow before dawn – July 19, 2017 – if you’re an early riser, look for the waning crescent moon near the sky’s brightest planet, Venus, and the red star Aldebaran. This star is the brightest in the constellation Tarurus the Bull. It represents the Bull’s fiery Eye. The July 19 morning moon is also in the vicinity of the Pleiades star cluster, aka the Seven Sisters, also in Taurus.
If you go outside too close to the sunrise, you might not see Aldebaran or the Pleiades; your sky might already be too bright. But you’ll easily 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 second-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.
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 Pleiades star cluster, the red star Aldebaran, and the planet Venus before dawn on July 19, 2017. On July 20, the moon will be even closer to Venus.
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.