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May 7: Io crosses Jupiter
Let’s take advantage of the moonless early-evening sky to enjoy two lovely face-on spiral galaxies. We’ll start at the brighter, easier option: M51, also known as the Whirlpool Galaxy. And it’s easy to find — it lies just 3.5° southwest of Alkaid (Eta Ursae Majoris), the star at the very end of the Big Dipper’s handle. At magnitude 8.4, this 11’-wide spiral is visible as a circular fuzz even in small scopes, though the larger your aperture, the better. Scopes 6 inches or larger will start to show more detail. Look for a small, brighter center surrounded by a faint halo — that’s the galaxy’s nucleus and spiral arms, respectively. You may also notice a compact, bright spot nearby. This is NGC 5195, a smaller companion galaxy.
Now let’s try hard mode: Go back to Alkaid, and this time move your scope 5.7° northeast. There you’ll find M101. Glowing at 8th magnitude and spanning more than 20’, this galaxy is challenging despite its similar brightness to the Whirlpool because it is so much larger. That means its glow is spread over a larger area, making it appear artificially dimmer (giving it what astronomers call low surface brightness). A large scope of 10-12 inches is recommended for the best view of this galaxy’s bright center and faint spiral arms.
Sunrise: 5:54 A.M.
Sunset: 8:00 P.M.
Moonrise: 12:12 A.M.
Moonset: 9:01 A.M.
Moon Phase: Waning gibbous (58%)
*Times for sunrise, sunset, moonrise, and moonset are given in local time from 40° N 90° W. The Moon’s illumination is given at 10 P.M. local time from the same location.
