This is Dudley Observatory’s Skywatch Line for Friday, April 26 through Sunday, April 28, written by Sam Salem.
On Friday, the Sun rises at 5:57am and sets at 7:50pm; the Moon reaches last quarter phase at 6:18pm; Moon rises at 2:07am and sets at 11:39am.
Mars, at magnitude 1.6, shines in constellation Taurus. It sets little before 11:30pm. Not long after that, Jupiter, at magnitude –2.4, rises as beacon in the southeast. Jupiter reaches the meridian when it’s positioned due south, a few minutes after 4am, just as morning twilight begins. Saturn, at magnitude 0.5, rises around 1:30am but doesn’t reach the meridian until shortly after sunrise. Both Jupiter and Saturn are rewarding telescopic planets right now. If you have a relatively unobstructed east horizon, you should have little trouble picking up Venus. The “morning star” gleams at magnitude –3.9 and pops up about an hour before the Sun.
One of the finest and most famous spring galaxies is M51, the Whirlpool Galaxy. Although it’s located in Canes Venatici, M51 is much easier to find by jumping off from Alkaid, also known as Eta (η) Ursae Majoris, the last star in the handle of the Big Dipper. At magnitude 8.1, the Whirlpool is fairly bright. However, its face-on orientation can make your observation more challenging than you may anticipate. At midnight this weekend, M51 is nearly overhead. Under a reasonably dark sky you can spot it with binoculars. In a modest scope the galaxy appears as a small, round glow with a brighter center. To see the spiral shape that gives the Whirlpool its name, you’ll need a bigger scope. The subtle spiral form of M51 can only really be described as obvious in a 12-inch or larger instrument.
The constellation Hercules, the Kneeling Giant, can be seen ascending in the east-northeast on spring evenings. You can find Hercules between the two brilliant stars Arcturus and Vega. Later in the evening, around 9pm or 10pm, the constellation Hercules and the two stars are well up in the northeastern to eastern sky. Arcturus is in the constellation Bootes, and Vega is in the constellation Lyra. A line between Arcturus and Vega passes through what is known as the Keystone, an asterism or noticeable pattern in Hercules. The Keystone is a square-like figure in the center of Hercules. Look for the Keystone asterism to the upper right of the brilliant blue-white star Vega. Hold your fist at arm’s length. Your fist fits between Vega and the Keystone. You can also locate the Keystone by using Vega in conjunction with the brilliant yellow-orange star Arcturus. The Keystone is found about one-third the way from Vega to Arcturus. Once you found the Keystone you will be able to find a famous globular star cluster in Hercules, otherwise known as the Great Cluster in Hercules, aka M13. You’ll need binoculars to see the Hercules cluster. Sharp-eyed people can see it with the unaided eye in a dark, transparent sky. Through binoculars, this cluster looks like a dim and somewhat hazy star. In a telescope you begin to resolve this faint fuzzy into a great big, globe-shaped, stellar cluster populated with hundreds of thousands of stars.