Scorpius the Scorpion

Scorpius the Scorpion
Anyone wary of spiders may want to avoid the spider's cousin whose blood red heart gleams in the southern sky. Most constellations don't look like their namesakes, but Scorpius can easily be imagined as a giant scorpion. Over three thousand years ago the ancient Babylonians named it MUL.GIR.TAB (“the creature with a burning sting”).

Scorpius is less overwhelming than it once was, for the Romans declawed the scorpion to make the constellation Libra. The two brightest stars of Libra still have names meaning northern claw and southern claw in Arabic.

Classical mythology
Scorpius is one of the oldest constellations, and part of the zodiac. Because of its position and antiquity, the myths and traditions surrounding it are numerous, and often contradictory. However in many of the classical myths the scorpion is the nemesis of Orion the hunter.

The giant Orion was a first-rate hunter, but he became arrogant and annoyed the immortals. In one story he foolishly laid hands on his hunting companion, the goddess Artemis. In another his crime was boasting of being such a great hunter that he could kill any living thing. Whatever his indiscretion might have been, the gods were quick to punish presumptuous mortals. Either Artemis or the goddess Gaia sent a scorpion to attack Orion, and there was a mighty battle. In the end the scorpion triumphed. His sting gave Orion a wound which couldn't be healed.

Zeus put the victorious scorpion in the sky. Orion is there too as a reminder to respect the gods. Yet they're kept well apart, with Orion a winter constellation and Scorpius a summer one.

Stars and planets
Scorpius is a bright constellation with over a dozen stars of the third magnitude or brighter. (The lower the magnitude, the brighter the star.) The most brilliant one is the heart of the Scorpion – Antares, a first magnitude red supergiant. Its name means like Mars in recognition of its bright red color. Antares is about sixty thousand times brighter than the Sun, and so big that if it were in the Sun's place, it would fill up all the space out to somewhere beyond the orbit of Mars.

Antares is also a binary system. Antares A is the supergiant, and it has a luminous blue companion. Antares B is much brighter than the Sun, but is swamped by the supergiant's glow. Austrian astronomer Johann Tobias Bürg was the first to see it when in 1819, Antares A was briefly occulted (hidden) by the Moon.

Lambda Scorpii, the scorpion's second brightest star, is at the tip of the tail. Its name Shaula means the sting. It's a triple star, and possibly a 5-star system. There's some evidence that Shaula A (the most massive of the three) might two unseen companions.

Theta Scorpii is a yellow-white star much more luminous than the Sun. It's also spinning so fast that it would look quite squashed. Its radius at the equator is nearly twenty percent bigger than its polar radius. It also has the distinction of being one of the twenty-seven stars on the flag of Brazil. Each of the stars represents a specific Brazilian state and Theta Scorpii symbolizes Alagoas.

A very unusual binary system is GRO J1655-40, some 11,000 light years away. It consists of a star about twice the mass of the Sun and a black hole about seven times the mass of the Sun.

A number of stars in Scorpius are known to have planets. The planets range in size from terrestrial to superjovian (bigger than Jupiter). The most exciting planetary system yet discovered is Gliese 667 C. The star is a red dwarf which is part of a triple star system about twenty-two light years away. There are at least six planets, all of which are terrestrial, three of them in the habitable zone of Gliese 667 C.

Deep sky objects
Three of the nebulae are named for their shapes.

The eye of the Blue Horsehead Nebula (IC 4592) is the star Nu Scorpii whose light is reflected in blue by nebular dust. A contrast to the blue nebula is the Cat's Paw Nebula (NGC 6334), an emission nebula discovered by John Herschel in 1837. Hot young stars energize hydrogen in the nebula, making it glow red.

Scorpius has both a Butterfly Nebula (NGC 6302) and a Butterfly Cluster (M6). The former is a beautiful planetary nebula created from the outer layers of a dying sunlike star. The latter is an open star cluster mainly composed of hot young blue stars, which makes its brightest star, orange giant BM Scorpii, stand out.

As well as open clusters, there are also globular clusters. One of the nearest to us is M4. It's visible even in a small telescope, and was the first such cluster in which individual stars were resolved. It contains some 100,000 stars, and formed when the Universe was a mere babe of a billion years old. (It's now 13.82 billion years old.)

Observing Scorpius
Scorpius is the Zodiac's southernmost constellation, so you can see it high in the sky in the southern hemisphere, but it's low on the horizon in the northern hemisphere. The best time for viewing is in July and August. In the northern hemisphere, it's visible up to about +40o with a clear southern horizon, and the top part of the constellation is visible somewhat farther north, such as the Britain.

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