Monthly
Messier Star-Hop; April #2
By
Art Russell
Have you noticed what’s happened in the northern skies over the past few months? Every year, at this time, we begin to notice that the Big Dipper has turned up-side down. In a sense, I guess it fits with mythology. The dipper turns up-side down and empties its water onto the Earth below; the real reason for April Showers! At the same time, as the Big Dipper rises higher into the northern skies, it also raises its circumpolar star fields high enough for prime viewing.
This month
we’ll spend our time with two of the many deepsky objects in the area
of the Big Dipper, the Mizar-Alcor double star system,
and the face-on spiral galaxy, M101. 
We start at the noted double star system of Mizar and Alcor, Zeta Ursa Majoris and 80 Ursa Majoris. Mizar is easily located as the star at the bend in the handle of the Big Dipper. Once you’ve found Mizar, you’ve found Alcor as well. Historically, at least since the 14th century Persians, the ability to separate Mizar and Alcor was held as a measure of good vision. Not surprisingly the Mizar – Alcor system was the first double star system to be studied with a telescope. As a result, it was discovered that they are really part of a multiple star system. Mizar has its own companion star, Mizar b. The observation of these two stars, Mizar a and Mizar b, is relatively easy with any good telescope and is quite striking given their relative magnitudes, 2.4 and 4.0, and wide separation of 14 arc seconds.
Our sole star-hop for this month is to M101, NGC 5457, a face on spiral galaxy. Take your time trying to find this galaxy, but be warned. You’ll want to be under dark skies in order to do so! M101 is located about 5 degrees (about the distance spanned by three fingers held at arm’s length against the sky) east of Mizar-Alcor and 5 degrees northeast of Alkaid, Eta (h ) Ursa Majoris, the last star in the handle of the Big Dipper. M101 is a low surface brightness galaxy which covers an area equal to about 2/3 of the full Moon’s. However, remember that this is galaxy will be very dim and easy to miss. Never the less, you can find it with small telescopes and binoculars under a dark(!) sky. In medium size telescopes at moderate magnifications, M101 appears about 20’ in diameter and has a very low level of surface brightness and is best seen in averted vision, with a hint of stellaring on northern portion of the galaxy. If you have access to a larger scope and or darker skies and are feeling adventuresome, try to find the HII regions associated with M101, NGCs 5447, 5461 and 5462. Additionally, you’ll find many other galaxies in the area as well. NGC 5474 is located about 1/2 degree south of M101 and in a large scope and high power may appear marginally visible in direct vision as a soft low surface brightness object. In averted vision, its surface appears mottled with scattered stellarings. The trip to M101 is also worthwhile if you are working on one of the several Astronomical League sponsored observing club certificates. M101 is one of the target objects of both the Messier Club, Binocular Messier Club, and the newly formed Arp Peculiar Galaxy Club. NGC 5474 is a target object for the Herschel 400 Club. Observe M101 and its companions and you’ll be well on your way to becoming a seasoned observer!