October offers some of the best skywatching conditions of the year. The nights are getting longer, while the weather is cooler but not frigid. The evening sky offers such treats as Andromeda and her famous galaxy, M31, as well as several other constellations associated with her mythological story. Other highlights include the two most prominent star clusters in the sky, the dipper-shaped Pleiades and nearby V-shaped Hyades, both in Taurus.
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In the Sky This Month
October 21: Little Dipper
The Little Dipper stands high above the Big Dipper, which is low in the northwest at nightfall. The Little Dipper’s bowl hangs upside down, like it’s pouring its water into the other dipper.
October 22: Pherkad
The star Pherkad, which forms the lower outer corner of the Little Dipper’s bowl, is much bigger, brighter, and heavier than the Sun. Over a period of a few hours, though, its brightness varies by a few percent, and astronomers aren’t sure why.
October 23: Moon and Saturn
Look for the planet Saturn near the crescent Moon early this evening. It looks like a bright star to the left of the Moon as twilight fades away. They set about three hours after the Sun.
October 24: More Moon and Saturn
Saturn, the solar system’s second-largest planet, huddles to the lower right of the Moon at nightfall this evening. Saturn has the largest ring system of any of the Sun’s planets, and the second-largest known retinue of moons.
October 25: Drawing Stars
Andromeda, the princess, is in the east and northeast at nightfall. It’s faint, though, so you need dark skies to see it. Andromeda is associated with several other constellations that share a common story.
October 26: Blue Snowball
One of the treasures of the constellation Andromeda, which is low in the east and northeast at nightfall, is the Blue Snowball Nebula, a bubble of gas expelled by a dying star. The nebula is at the right edge of the constellation, above the Great Square of Pegasus.
October 27: First-Quarter Moon
The Moon is at first quarter today. It rises in early afternoon and sets around midnight. At first quarter, sunlight illuminates exactly half of the lunar hemisphere that faces Earth, so it looks as though someone sliced the Moon down the middle.