The solar system’s largest planets put in large appearances this month. Jupiter, the biggest of them all, was at opposition last month, so it’s still in view most of the night and still shining brilliantly, making it an especially easy target. Saturn, which ranks just behind Jupiter, is at opposition this month, so it, too, is a large presence in the night sky. Its rings are tilted at a fairly open angle, so their reflected sunlight adds to Saturn’s overall brightness.
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In the Sky This Month
July 21: Dog Days
Mid-summer is called the Dog Days because the “dog star,” Sirius, appears near the Sun. Since Sirius is the brightest star in the night sky, ancient skywatchers associated it with especially hot days.
July 22: Starry Sky
When darkness falls tonight the sky will come alive with stars: the Summer Triangle up in the east, the scorpion low in the south, and the stars of spring sliding from view in the west.
July 23: Outcast Stars
The Big Dipper is in the northwest this evening, with the handle above the bowl. The five stars in the middle of the dipper are all related, but the stars at the tip of the handle and lip of the bowl move through the galaxy independently of the others.
July 24: Last-Quarter Moon
The Moon reaches last quarter at 8:18 p.m. CDT. It lines up at a right angle to the line between Earth and Sun, so sunlight illuminates exactly half of the lunar hemisphere that faces our way.
July 25: Distant Planet
The constellation Virgo is in the southwest at nightfall. Astronomers recently discovered a big, heavy planet orbiting one of its stars, HR 5183. The system is about 100 light-years away.
July 26: Moon and Aldebaran
The Moon will flirt with Aldebaran, the brightest star of Taurus, the next couple of mornings. The star will stand to the lower left of the Moon at first light tomorrow, and about the same distance to the upper right of the Moon the next day.
July 27: The Dolphin’s Snout
A pretty binary star system climbs across the southern sky on summer nights. Gamma Delphini represents the snout of Delphinus, the dolphin. The little constellation is in the east as night falls, with the snout on the left and the tail on the right.