When you look up near the top of the sky around 10:30 p.m. in mid-July you can’t miss the brilliant white star Vega. It sparkles just to the left of due south. Shoot a line from Vega a little more than one outstretched fist to the right and you’ll arrive at … nothing!
OK, I’m exaggerating, but at first glance, it looks pretty empty up there. A closer look will show a pattern of faint stars that make up the large, sprawling constellation Hercules the Hero. Known in ancient Greek myth as Heracles, this heroic figure is perched upside-down near the zenith at nightfall in July.
At the center of Hercules is something you can focus on – a group of four stars in the shape of a trapezoid called the Keystone. Along its right side is one of the finest star clusters in the summer sky.
The cluster’s name, the Great Globular Cluster in Hercules, sounds practically generic, but it’s snappier than M13, the number 18th century astronomer Charles Messier gave to it in his catalog of fuzzy objects that resembled comets.
From rural skies, M13 is a little fuzzy patch visible to the naked eye if you know just where to look.
Binoculars bring out its two-part structure – a brighter core surrounded by a fainter halo. In telescopes as small as 4 inches you begin to see what all the excitement’s about as the outer haze begins to resolve into a starry sprinkles. Bring an 8-inch or larger scope to the task and M13 scintillates with hundreds (thousands?) of stars. Let’s just say too many to count.
Hercules’ Great Globular was discovered by Edmund Halley of Halley’s comet fame in 1714 and belongs to a class of dense, spherical-shaped assemblies of stars called globular (GLOB-you-lur) star clusters.
I always tell people to buy a telescope – or at least find one to look through – if only to see the planet Saturn, the single most amazing sight in the universe. Globulars come in a close second. The throng of stars that meets the eye through 8-inch and larger instruments is nothing short of stunning.
Hercules is also home to a very special spot called the solar apex, shown in the first map above. This is the direction in which the sun is traveling as it orbits the nucleus of the Milky Way galaxy. As seen from the galaxy’s north pole, the sun, with planetary bling in tow, circles around the galaxy in a clockwise direction at 137 miles per second. Sounds fast, doesn’t it? Not fast enough. Our galaxy’s so big it still takes the sun 225 million years to go around once. Astronomers call one full cycle a cosmic year. Life on Earth began only 15 years ago – cosmic years that is.
Other stars and gas clouds in the sun’s vicinity travel at nearly the same speed, moving very little with respect to one another. It’s not unlike a multi-lane road where everyone is traveling at 35 miles an hour in the same direction. Very frustrating if you’re trying to pass.
Aside from this general streaming motion around the galaxy, the sun has a slight additional motion of 10 miles per second in the direction of the constellation Hercules southwest of Vega. When you go out the next clear night and gaze almost straight up at nightfall, picture yourself on a very long journey with our hero Hercules.