July Evening Skies

By Rod Kennedy

July brings nearly oppressive heat to Wyoming and that heat tends to drive some animals to seek cooler hiding places.  These include lizards, snakes and even scorpions.  Although the scorpions in some parts of Wyoming are fairly small, they are nocturnal predators that are deadly to their prey.  However, there is one kind of scorpion that visits Wyoming in July that is larger than any on Earth.  This giant is none other than Scorpius the Scorpion; and it stays in our evening skies well into the autumn.

Scorpius is a very easy constellation to find for two reasons.  The first is that it is one of the few constellations that actually look like what it is supposed to represent.  The second is that a very bright star, Antares, the heart of the Scorpion, marks Scorpius.  Antares literally means ‘rival of Mars’ because of its reddish orange color.  However, Antares is bright because it is a red super giant star.  Red stars are the coolest of all stars, and therefore seem much dimmer than their blazing blue or white cousins.   In addition, Antares lies 604 light years away.   These two pieces of information tell us that Antares, which is cool and far away must be very large.  In fact Antares has a diameter 700 times that of our own sun.  Its huge size makes Antares 9000 times as luminous as our small average sized yellow star.

Scorpius is one of the constellations that lay along the line known as the ecliptic.  This line is the plane of our solar system and the sun, moon and visible planets can be found within a couple of degrees of this line.  Strangely enough however, the constellations along the ecliptic have changed somewhat from ancient times.  Originally the claws of Scorpius extended to include the stars we now know as Libra the Scales.  Sometime later Libra became a constellation in its own right.  In 1930 the International Astronomical Union officially set boundaries where one constellation ends and another begins.  These boundaries, rather like state lines, ensured that every object in the sky would fall within a specific constellation.  Ironically, by setting these boundaries the IAU added a 13^th constellation to the Zodiac.  Today, the Zodiac included the constellation Ophiuchus the Serpent Bearer.  Ophiuchus is north and slightly east of Scorpius, but the constellation boundaries cause the ecliptic to pass through this difficult to find constellation.

East of Scorpius is Sagittarius, the Archer.  Unlike Scorpius, Sagittarius doesn’t look like the mythical Centaur that its name represents.  Instead it looks more like a teapot with the spout pointing west toward Antares.  The area around Scorpius and Sagittarius offers telescope users a treasure trove of objects for observing.  There are literally dozens of nebulae; open and globular star clusters, and variable stars.  The reason for the wide range of objects is the fact that when we look to Scorpius and Sagittarius we are looking toward the center of our Milky Way galaxy. 

For those who don’t own a telescope, you can still catch a glimpse of these deep sky wonders.  Contact your local astronomy club; most of them host free public telescope observing sessions or “star parties” thorough out the summer.   These events are great opportunities to see the wonders of the sky and also try out many different types of telescopes.  Plus most astronomy club members are quite happy to share their knowledge and expertise about the sky.