Some Treasures of the Summer Milky Way From Perseus to Sagittarius
July 2013 :
Last month I lamented the fact that during the summer months amateur astronomers have to wait so long before darkness falls before we can begin our observing sessions. However, as the saying goes, “Good things come to those who wait.” For once twilight fades we can focus our attention, binoculars and telescopes on the majesty of the summer sky and all the astronomical treasures it contains.
At 10:30 pm during the beginning of July, from a sky not severely limited by light pollution, an observer will notice a milky patch of light well above the eastern horizon and spanning the sky from north to south. Though an inexperienced observer may mistake this glow as thin cirrus clouds, it is really the light from some of the 400 billion stars of our Milky Way galaxy. We view it from a vantage point about two-thirds of the way out from the galaxy center in one of its four spiral arms. This perspective, gained from a great distance, allows us to observe it as a flattened disk with a central bulge.
While the mythology of the constellations up and down the Milky Way is truly fascinating, I only wish to highlight some of the beautiful sights that can be observed. There is something here for everybody. You can simply use your unaided eye, or grab that pair of binoculars from the closet or drawer (7x35s or 7x50s work very well for this task), and scan the entire length of that hazy cloud of starlight.
We’ll start our brief Milky Way tour in the northern sky. (Download a free planisphere/star wheel at http://www.lawrencehallofscience.org/starclock/starwheel.pdf.) Locate the constellation of Cassiopeia which is shaped like the letter W. Farther towards the north is Perseus. Between the two patterns we can easily see the Double Cluster with the naked eye. While binoculars will enhance the view, a telescope under low magnification will reveal the magnificent beauty of this open cluster of stars.
Our next stop “down” (south) the Milky Way is the constellation Cygnus the Swan (also known as the Northern Cross). This celestial avian is immersed in the myriad of stars that comprise the Milky Way. More than likely you’ll recognize the pattern of a cross before you see a swan in these stars. It is here in the Cygnus region where the Milky Way divides into two bands, separated by obscuring dust called the Great Rift. Take a look with binoculars to start with and scan this area. It is a very beautiful region of space. If you have a telescope of any size, don’t hesitate to sweep this area. Agnes Clerke, a late 19th- and early 20th-century astronomy writer described Cygnus as “perhaps the most lovely effect of colour in the heavens.” Indeed, there are more red and orange colored stars in this region of space than anywhere else in the sky. The red stars are most striking. You will be well rewarded for your search efforts.
Deneb, the northernmost and brightest star of the constellation, forms the top of the cross (or the tail of the swan). Use binoculars to locate a large open cluster of stars north of Deneb. It’s called M39. Objects with the “M” prefix were catalogued by French astronomer Charles Messier (1730-1817) while he was hunting for comets. M39 contains about 20 bright stars. A low-power eyepiece on a small telescope will allow the object to fill the entire field of view.
Just south from Sadr, the center star of the cross, one can find another open cluster called M29. This cluster is more compact than M39 and only contains about eight bright stars. The four brightest stars of this group form a square. The cluster can be found using binoculars, but a low-power telescope will enhance the view.
Head farther down the Milky Way from Sadr and you’ll come to Albireo at the base of the cross. Albireo means “beak,” and represents the beak of our swan. This gem is one of the finest double stars in the sky. It seems double star observers have always tried to outdo one another when describing the often contrasting colors of the star system pairs they were observing. For instance, the components of Albireo were described as topaz yellow and sapphire blue. Well, I call them the Cub Scout stars, blue and gold. The scouts who visit us at Seagrave Observatory certainly like that description.
Continuing our journey south we come to the constellation of Scutum and a star cloud of the same name. In a dark sky, your eye will see a much greater expanse of milky haze. This eastern band is one of the brightest in the Milky Way because there is no intervening dust and gas to block our view of the stars. Astronomer E.E. Barnard (1857-1923) wrote, “the stars pile up in great cumulus masses like summer clouds.” A prominent open cluster, M11, also known as the Wild Duck Nebula, can be found here.
As we continue our journey down the Milky Way we encounter star rich regions of our galaxy. We can observe many open clusters of stars, like M21, M23 and M25 in Sagittarius. While in one mythological tale this star pattern represents an archer, today Sagittarius is more recognizable as a teapot. In fact, with the handle to the east and the spout to the west, the Milky Way appears to be steam pouring forth from it. Along the way we encounter the Eagle Nebula (M17) in Serpens Cauda, and intriguing nebulae with names like Trifid (M20) and Lagoon (M8) in Sagittarius.
These highlights are just the tip of the proverbial iceberg for celestial sights to observe within our home galaxy. I hope you will take an opportunity to tear yourself away from your television, computer screen and mobile device to spend some quality time gazing at the beauty of the Milky Way.
Dark skies do still prevail at some of the local observatories where you can explore the Milky Way with other sky enthusiasts. Seagrave Memorial Observatory in North Scituate is open every clear Saturday night. Ladd Observatory (http://www.brown.edu/Departments/Physics/Ladd/) in Providence will reopen on Tuesday, July 16, providing the sky is clear. Frosty Drew Observatory (http://www.frostydrew.org/) in Charlestown’s Ninigret Park is open every clear Friday night year-round. Be sure to check all the websites for the schedules and opening times before visiting these facilities.
Keep your eyes to the skies.
When to Observe
Summer Mikly Way rising at Frosty Drew Observatory by Scott MacNeill.
