Another hero in the sky
By Vernon Whetstone
Orion is not the only celestial strong man in the sky. Now that he has exited stage-right for the summer, there is another constellation depicting a mythological hero taking his place, Hercules.
Strangely, Hercules clears the eastern horizon in the same manner as our old friend Orion—he is laying down, parallel to the horizon with his head to the right and his feet to the left.
Hercules is the fifth largest constellation in the sky and though it has a Greek name, it was also known in antiquity to Babylonian astronomers. It is not a very bright constellation, most of its stars are no brighter than third and fourth magnitude.
The most prominent feature of Hercules is an almost rectangular shape in the middle called “The Keystone.” It represents the body of our hero. It can be best found by drawing a line from bright Vega to the lower left up and right to another bright star we have visited before, Arcturus, in Bootes.
As one claim to fame, Orion boasts the beautiful, gaseous nebula, M42, the Orion Nebula. Hercules also has a couple of extra added attractions, both are very nice globular star clusters equally visible using binoculars.
The first is M13, which is probably the brightest globular in the northern hemisphere. It can be located this month by looking east after 9pm MDT on the top side of the Keystone toward the left end.
From a very dark sky location away from city lights, M13 can be seen with just the eyes alone as a faint, fuzzy spot. In binoculars it takes on the fuzzy form of thousands of stars grouped in a tight cluster.
The other globular cluster, M92, is located about 10 degrees from M13, to the left of the Keystone between the legs. It is smaller than M13, but can still be seen very well in binoculars.
A word about the difference between a globular star cluster and an open star cluster. An open star cluster consists of many stars in a loose grouping held together by mutual gravity numbering into the hundreds.
They are found throughout the spiral arms of the Milky Way Galaxy. Good examples of open clusters are M44, the Beehive star cluster in Cancer, and M45, the Pleiades star cluster in Taurus.
Whereas a globular cluster is an often large group of stars numbering into the thousands, again, held together by mutual gravity, but are located in close orbit around the center of the galaxy such as M13 and M92.
There are also a number of nice double stars located in Hercules. A slow scan with your binoculars will be rewarded.
SKY WATCH: Third Quarter moon On Friday, May 31. This week continues the triple-planet, planetary conjunction in the west after local sunset. Watch each night during this week into next as Jupiter, on the bottom, through bright Venus in the middle, to dimmer Mercury on the top, move into a straight-line formation going from the horizon up following the ecliptic.
As the week progresses, Venus and Mercury rise higher and Jupiter sinks lower toward the horizon leaving the sky totally by the first week of June.
Have your binoculars handy for the evening of June 4, when Venus will masquerade as a member of the open star cluster, M35, and then in July Venus will cozy-up with M44.
NEXT WEEK: Another astronomical giant, and more astronomical blather.