The head of Scorpius the Scorpion with its bright star Antares reachest its highest altitude in the southern sky this time of year. It’s ideally placed for viewing at the end of evening twilight a little more than two outstretched fists above the southern horizon. Details: 35mm f/2.8, ISO 800 and 20 second exposure. Photo: Bob King
Most of us don’t have ideal skies. We live with light pollution and views of the celestial sphere that are compromised by trees and buildings. I know how good it feels when every so often I drive out to a treeless, open place and experience the starry sky all around me. It’s positively liberating when the barriers to the cosmos are removed. But most of the time I’m like you and have to contend with missing pieces of the sky. One piece missing from my neighborhood is the bottom 20 degrees of the southern sky, which prevents a complete view of one of the coolest of the 88 constellations, Scorpius the Scorpion. Cool because it’s one of the few that really resembles its name.
The view of Scorpius is compromised for observers in the northern U.S. but not by much. If you do have access to an observing spot with an open horizon to the south, you’ll be able to see all the way down to Shaula, also called the "Stinger" star in the scorpion’s tail. Maps created with Stellarium
Scorpius never rises very high for sky watchers at mid-northern latitudes, so I’m going to guess many of you are in the same situation as I am. From my home, only the head of the Scorpion clears the trees on June and July evenings. Much of the tail is hidden by branches and leaves, while the very bottom of the constellation scrapes the horizon. We northerners content ourselves just the same with the pleasures of red Antares, the scorpion’s brightest star, and the three-stars-in-a-row that form the head, a summertime version of Orion’s famous Belt.
As Donald Trump might say, Antares is "YOOGE!". While cooler than the sun, it more than makes up for its dimmer surface by sheer size. That’s the reason it shines brightly despite its considerable distance of 600 light years. In the diagram, R stands for radius which is equal to 1/2 the diameter.
In contrast to the tiny stars we’ve been examining over the last week, Antares is a red supergiant 800 times the diameter of the sun. Its expansive girth would fill the solar system beyond the orbit of Mars if it plopped in place of the sun. The Mars connection is an apt one, since the name Antares comes from the ancient Greek "anti" and "Ares" or Rival of Mars, referring to its color which is nearly identical to the planet.
Traveling this summer? If you’re headed south or if you live in the southern U.S. , you’ll have better luck than us northerners at seeing the complete scorpion. For every degree of latitude you drive or fly south, the stars in the southern sky rise higher by an equal amount. One degree is equal to two full moons side by side.
Sky watchers in the central and southern U.S. might be more familiar with the whole scorpion. As you travel south of my town along the curvature of the Earth, the stars in the southern sky rise ever higher while those in the north drop closer to the northern horizon. By the time you’ve reached Denver’s latitude of 40 degrees north, Scorpius’ tail easily clears the horizon. Continue to New Orleans and it literally sails across the sky. There are many deep sky treats in Scorpius for both binocular and telescope users, not to mention the Milky Way is magnificent there when seen from a dark sky. Tomorrow we’ll drop in on a few of these beauties.