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Northern Rockies Skies for August

July 26, 2012

A monthly look at the night skies of the northern Rocky Mountains, written by astronomers Ron Canterna, University of Wyoming; Jay Norris, Challis, Idaho Observatory; and Daryl Macomb, Boise State University.

What a great time to view our home galaxy, the Milky Way. Around 10 p.m., this subtle, hazy band of stars is high in the southern sky and is best explored with the naked eye and binoculars. The "milky way" is a myriad of faint stars and dark dust lanes confined to one plane.

The constellations Scorpius and Sagittarius, the teapot, mark the direction to the center of our galaxy, located on the southern horizon. The scorpion contains the brilliant red star, Antares.

Directly overhead, the bright star Vega dominates most of the night. It is the brightest star in the constellation Lyra. Also overhead, the Milky Way traverses the Northern Cross and Cygnus the Swan, and then plunges into the northern horizon through Cassiopeia, the big "W" in the sky.

Note that the Milky Way "haze" is broken up by very prominent dark patches. The dark patches are dust lanes that are projected against the background of fainter stars, blocking out their distant light. Also, a large number of star clusters can be easily recognized with binoculars.

Planet watch: At sunset, note that Saturn and Mars are close together -- near Spica in Virgo -- on the southwest horizon. Right before sunrise, you will see a spectacular display of Jupiter, Venus and Mercury (if lucky) as you look toward the east horizon.

August2012 Interest -- Famous Astronomers:  Fraunhofer
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In his youth, Joseph Fraunhofer (1787-1826) was an orphan, consigned as an optician's apprentice in a glassmaker's workshop. When the building in which he worked collapsed, he was rescued by the future first king of Bavaria. This was a fortunate circumstance that led to the furthering of Fraunhofer's education and advancement toward scientifically oriented circles.

Fraunhofer invented a machine to polish the spherical surfaces of large object glasses very accurately, and many other devices for grinding and polishing optics. He improved the quality of crown glass for large telescopes. In 1818, his contributions had become so important that he was appointed director of the Optical Institute in Bavaria, which overtook England as the center of the optics industry.

By a combination of methods, Fraunhofer most notably achieved the production of light sources of homogeneous wavelength, which he then used to measure the refractive power of glasses. This was a necessary step toward his invention of the first spectroscope of the prism variety.

Fraunhofer trained his telescope, outfitted with a spectroscope on the sun, and discerned more than 500 dark spectral lines. Later, in the mid-1800s (after his death), physicists determined these dark lines to arise by atomic absorption in the sun's photosphere of light emanating from lower layers. Spectroscopy is a primary method by which assays are made of elemental and molecular abundances in stars and terrestrial samples. The solar lines he discovered are still referred to as Fraunhofer lines.

He also developed wire diffraction gratings, more often used in modern spectroscopes as the light- dispersing element in lieu of a prism; as well as microscopes and heliometers. The latter instrument was used to measure stellar parallax, one of the primary methods for determining stellar distances.

In the early era of glassmaking, many workers succumbed to poisoning by heavy metal vapors, as did Fraunhofer at the age of 30. Many people think he took many of his glassmaking recipes to the grave.

To view this month's sky chart, click here.

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