This is Dudley Observatory’s Skywatch Line for Friday, October 12 through Sunday, October 14, written by Sam Salem.
On Friday, the Sun rises at 7:05am and sets at 6:18pm; the waxing crescent Moon rises at 10:41am and sets at 8:48pm. On Sunday evening, the crescent Moon approaches Saturn.
Jupiter, at magnitude –1.8, is viewable for only a short while this weekend. It shines low in the southwest and sets roughly 1½ hours after the Sun. Saturn, at magnitude 0.5, is a little past the meridian 45 minutes after sundown. Saturn is easy to spot in northern Sagittarius. East of Saturn is Mars, at magnitude –1.1, near the center of the V-shaped constellation Capricornus. Mars is now considerably fainter and smaller. Mars still offers some good telescopic views. The best time to look is when Mars is at the meridian, around 9pm.
This weekend, watch two of the finest autumn globular clusters, M15 in constellation Pegasus, and M2, nearby in constellation Aquarius. Both globulars can be spotted in binoculars. M15 is easy to locate just northwest of the 2.4-magnitude star Enif, or ε Pegasi. M2 sits north of 2.9-magnitude Beta (β) Aquarii.
In a telescope, each cluster appears nicely symmetrical with a bright, highly concentrated core surrounded by a fringe of faint stellar haze. Both clusters are at magnitude 6.2 and span roughly 12 arc-minutes. However, with thorough observation you will find out that these globulars are not identical.
Use the Summer Triangle and the constellation Cygnus, the Swan, to locate the galactic equator, the great circle on the celestial sphere that bisects the glowing band of stars of the Milky Way. It’s the autumn season, but the three brilliant stars that make up the Summer Triangle still shine in our sky. They sit way up high on October nights. The stars Deneb and Vega hang high overhead at nightfall and early evening. Vega, the brightest Summer Triangle star, shines to the right of Deneb, and Altair, the second brightest, is found roughly halfway between southern horizon and straight overhead. As evening deepens, look for a star to pop out in between Altair and Vega. That’s Albireo. It depicts the Swan’s eye or beak. The line from Albireo to Deneb shows the underside of the Swan’s body from head to tail. Three stars cross the body near Deneb to form what is known as the Northern Cross. Go one star farther out on each side of the Northern Cross to finish off the Swan’s wings. Extend the Albireo to Deneb line in either direction to mark the galactic equator. Through binoculars, you’ll see that star clouds, star clusters and nebulae abound on this great galactic line.
Starting Saturday morning, the zodiacal light should be visible in the predawn as a faint, extended glow stemming from the east horizon. Zodiacal light is produced by sunlight reflecting off dust particles in the Solar System. Zodiacal light is best seen during twilight after sunset in spring and before sunrise in autumn, when the zodiac is at a steep angle to the horizon. However, the glow is so faint that moonlight and light pollution outshine it.