Star Points for July, 2000; by Curtis Roelle Scorpion's Tail Delights Observers. Have you ever tried locating a constellation in the sky only to find yourself lost amid the stars so that you throw up your arms just wanting to forget the whole thing? Being equipped with the right kind of chart helps. A too simple chart might not show enough stars to match up with what you are seeing. A chart that is too detailed includes far more stars than you can see with the unaided eye alone causing confusion. It also would help if the star pattern you are looking for had any resemblance to the animal, object, or being it is supposed to represent. Fortunately, there are a handful of constellations that more or less do resemble the characters of their namesake. For example, in the winter Orion stands high in the southern sky. His belt, shoulders and knees are easily recognizable. In a dark country sky his club, shield, and dangling sword are easy to pick out amid the stars. This month low in the southern Summer sky the constellation Scorpius the scorpion beckons. It too has an easily recognizable star pattern and later I will point out where you can find an on- line constellation chart on the web. Also we will be discussing a couple of rich star clusters found in Scorpius. Both of these are visible in small telescopes as well as binoculars. But first a short note about the constellation's correct name. In old star atlases such as Johannes Bayer's "Uranometria" (1603) and Alexander Jamieson's "Celestial Atlas" (1822) the constellation is labeled "Scorpio". The contemporary use of this name however is typically in connection with the astrology superstition. When discussed in the context of astronomy the proper name to remember is Scorpius. I prepared a star chart using the "shareware" program Skyglobe and have put it on the star points web page at http://www.erols.com/roelle/starpoints/. To view it go to the bottom of the page to the section labeled "Star Points Illustrations". Click on "Scorpius" to view the chart. In mid-July Scorpius appears to stand on its tail just above the southern horizon at around 10 p.m. daylight time. The green line at the bottom of the chart represents the observer's horizon when facing south. Scorpius' brightest star Antares marks the position of the scorpion's heart. Antares is a 1st magnitude star and is the 16th brightest star in our sky in apparent brightness. A noticeably orangish tinge makes Antares easy to recognize. Also it is the brightest southern star during evening hours this month. The claws of the original scorpion have been lopped off to form the constellation of Libra the scales. The stars to the upper right of Antares form the scorpion's head. The line passing west to east through the head in the web chart mentioned above is the Ecliptic. Each year on November 25-26 the Sun is located on the ecliptic within the head of Scorpius. The tail snakes down toward the horizon and then curls upward where the stars marking the "stinger" are located. The base of the curve just brushes along the horizon. If you are plagued by nearby buildings or trees you may need to find higher ground to view the tail region. Two large star clusters are located just above the "stinger" of the tail. On the chart these are seen as blob shapes near the center of the left edge. From a dark sky site both clusters are visible to the unaided eye. From most locations they are easily viewed with only slight optical aid such as binoculars. Both star clusters are of the type known as "open" or "galactic" clusters. Open star clusters appear as a loose grouping or scattering of stars. The reason they are clustered is that they formed together from the same intra-galactic cloud of dust and gas. The upper cluster is Messier 6, or simply M6. The cluster consists of about 80 stars most of which are concentrated in an area that is about half the diameter of the full moon. In a telescope the cluster is best viewed with low power. I have noticed numerous curved arcs of stars which create a beautiful and pleasing image. These arcs might explain why the cluster is sometimes called the "Butterfly Cluster." To the lower left of M6 is the larger open cluster M7. M7 was known as far back as the time of Ptolemy who mentioned it around 130 AD. He described M7 as a "nebula following the sting of Scorpius." With the unaided eye the individual stars are too close and faint to be distinguished. Instead, the cluster appears misty or nebulous. M7 is another fine binocular object. A telescope will resolve more stars and start picking up the fainter ones. At low magnification I noticed several chains of stars dominating the cluster. Two perpendicular straight lines of stars catch the eye. The star points web site also has photographic images of M6 and M7. Just scroll to the bottom of the page and click on Messier 6 or Messier 7.