For the week including July 30, 2010
THE SHIELD
After sunset, the constellation of Sagittarius, the Archer, stands out among the stars in the southeast. This large constellation is fairly easy to locate because its brightest stars suggest a child’s drawing of a teapot. If the Teapot asterism didn’t stand out so well, we would have a much harder time finding the much smaller constellation of Scutum, the Shield. Scutum doesn’t contain any bright stars, but amateur observers need only scan above the Teapot’s lid to get to it.
The constellation of the Shield was one of a series of constellations invented by Johannes Hevelius in 1684. It symbolizes the shield of King John Sobieski III of Poland. That name may not ring a bell to people nowadays, but Sobieski had a profound effect on European history. Starting in the 13th century, Turkish states banded together and absorbed or conquered territories in Europe, Asia and Africa, creating the Ottoman Empire. When the Turks captured the great city of Constantinople in 1453, the people of Europe lived in fear of the empire’s domination. In 1683 John Sobieski led an international army against the Ottoman Empire at a battle near Vienna and won a great victory that halted Ottoman expansion into Europe. Hevelius commemorated Sobieski’s triumph by placing his shield among the stars of an atlas he would publish as Firmamentum Sobiescum in 1690.
Gathered near this “Y” shaped group of stars are several beautiful deep-sky objects that are visible to the naked eye or with the aid of binoculars:
M17, the Swan Nebula (lower squared area): A huge cloud of hydrogen, helium and other gases, M17 is one of the brightest star-forming regions visible from Earth. Look at it closely with a backyard telescope and you’ll see that a portion of its clouds take the shape of a beautiful swan with a sprinkling of newly-hatched stars gathering around it. M17, shown at upper right, measures over forty light years across and is the second brightest nebula visible in our galaxy. Easily found with a good pair of binoculars, astronomers estimate M17’s distance as roughly over 5,000 light years.
M16, the Eagle Nebula (upper squared area): Made popular among the general public by the Hubble Space Telescope’s spectacular close-up images, the Eagle Nebula has been a favorite of astronomers for over a century. Shown at lower right, binoculars will bring out its bright clouds and accompanying stars.
M11, the Wild Duck Cluster (circled area): Shown at upper left, M11 is perhaps the most beautiful of the open star clusters. It contains thousands of stars of varying brightness, but the average telescope reveals hundreds of them. On good nights, the cluster is visible to the unaided eye. Its nickname comes from an Admiral William Smyth of Scotland, who in 1844 said it resembled a flight of wild ducks.
He was mistaken.
The photograph by David Malin of M17 is from the Australian Astronomical Observatory
The photograph of M11 is from the Canada-France-Hawaii Telescope / Coelum
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