Fly me to the cross: the Milky Way gets top billing in June's evening sky.
Wouldn't it be wonderful if we could all fly to the Moon? While that might be in the pipeline for the future, amateurs today can fly just about anyplace they want on Earth (something that was more of a luxury in 1956). As such, an increasing number of northerners make it to southern latitudes where they can enjoy the rich bounty of our southern skies. Observers in the Southern Hemisphere, and indeed also in Northern Hemisphere latitudes near the equator, often admire the Southern Cross. While it is the smallest constellation, it is easily one of the most distinctive and famous. Crux, as it is officially known, is just one highlight of a truly spectacular southern Milky Way that is on show at this time of year.
Crux's lucida is 0.8-magnitude Alpha ([alpha]) Crucis. The twelfth brightest star in the night sky, it is also the sky's southernmost 1st-magnitude star. Alpha Crucis is a brilliant double star easily split in small telescopes. The 1.4-magnitude primary has a companion 4 arcseconds distant and only 1/2 magnitude fainter. Both stars appear bluish white.
Four other stars make up Crux's eye-catching outline--Beta ([beta]), Gamma ([gamma]), Delta ([delta]), and Epsilon ([epsilon]). Near Beta Crucis lie two outstanding treats for binoculars and small telescopes. The most noticeable one is the Jewel Box, NGC 4755, an open star cluster that easily ranks as one of the finest in the sky. It's a must-see destination when I take my telescope to public astronomy nights. Closer to Beta is DY Crucis, popularly known as Ruby Crucis. This carbon star looks strikingly red and varies in brightness between magnitude 8.4 and 9.8.
Under a dark sky, away from urban lights, naked-eye observers see a large cloud blotting out part of the Southern Cross. Called the Coalsack, it's the sky's most prominent dark nebula, lying some 600 lightyears from us. European explorers first sighted it around the end of the 15th century, and it's sometimes called the Black Magellanic Cloud, though this appellation has never gained the popular usage of its luminous brethren, the Large and Small Magellanic Clouds, a pair of companion galaxies to our own Milky Way.
The starry background that enhances the Coalsack's appearances is due, of course, to the Milky Way arcing across this region of the sky. Our galactic plane, in its great circle around the sky, reaches its southernmost point in Crux. Indeed, this point falls within the Coalsack, about 3[degrees] south of the Jewel Box. (The galactic plane's northernmost point lies near the star Gamma Cassiopeiae, which never rises above the northern horizon from latitude 35[degrees] south, for which the facing chart is drawn.)
The southern Milky Way has been woven into its fair share of science fiction, and that's not surprising considering it is home to Alpha Centauri, the closest stellar system to us. But Crux has starred too. In the popular 1975 novel The Mote in God's Eye, authors Larry Niven and Jerry Pournelle use the Coalsack as the setting for a human interstellar voyage.
The Coalsack isn't confined to Crux, however. It extends over the border into neighboring Musca (the Fly), and Centaurus (the Centaur). Musca is twice the size of Crux, but it is far less conspicuous with just two stars of 3rd magnitude and several of 4th. For deep-sky observers, its attractions lie in two globular clusters (NGC 4833 and NGC 4372), a planetary nebula (NGC 5189), and a dark nebula that is popularly known as the Dark Doodad. As seen on photographs, this dark nebula is an absolute treat.
But here's a tip: Just step outside on the next clear night, look up, and undertake your own personal voyage of discovery. You too can fly to the stars.
Contributing editor Greg Bryant can be reached at firstname.lastname@example.org.
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|Publication:||Sky & Telescope|
|Date:||Jun 1, 2006|
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