David Wills

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APOD: Perseid Meteors Over Ontario (2013 Aug 13) Image Credit & Copyright: Darryl Van Gaal; Annotation: Judy Schmidt http://apod.nasa.gov/apod/ap130813.html Explanation: Where are all of these meteors coming from? In terms of direction on the sky, the pointed answer is the constellation of Perseus. That is why the meteor shower that peaked over the past few days is known as the Perseids -- the meteors all appear to come from a radiant toward Perseus. Three dimensionally, however, sand-sized debris expelled from Comet Swift-Tuttle follows a well-defined orbit about our Sun, and the part of the orbit that approaches Earth is superposed in front of the Perseus. Therefore, when Earth crosses this orbit, the radiant point of falling debris appears in Perseus. Pictured above, a composite of 13 early images from this year's Pereids meteor shower shows many bright meteors that streaked through the sky the night of August 11 near Oakland, Ontario, Canada. http://darkclearskies.blogspot.com/ http://www.geckzilla.com/ Starship Asterisk* • APOD Discussion Page http://asterisk.apod.com/discuss_apod.php?date=130813 #APOD

APOD: Nova Delphini 2013 (2013 Aug 16) Image Credit & Copyright: Jimmy Westlake (Colorado Mountain College) http://apod.nasa.gov/apod/ap130816.html Explanation: Using a small telescope to scan the skies on August 14, Japanese amateur astronomer Koichi Itagaki discovered a "new" star within the boundaries of the constellation Delphinus. Indicated in this skyview captured on August 15 from Stagecoach, Colorado, it is now appropriately designated Nova Delphini 2013. Sagitta, the Arrow, points the way to the newcomer's location high in the evening sky, not far from bright star Altair and the asterism known to northern hemisphere skygazers as the Summer Triangle. The nova is reported to be easy to spot with binoculars, near the limit of naked-eye visibility under dark skies. In fact, previous deep sky charts do show a much fainter known star (about 17th magnitude) at the position of Nova Delphini, indicating this star's apparent brightness suddenly increased over 25,000 times. How does a star undergo such a cataclysmic change? The spectrum of Nova Delphini indicates it is a classical nova, an interacting binary star system in which one star is a dense, hot white dwarf. Material from a cool, giant companion star falls onto the surface of the white dwarf, building up until it triggers a thermonuclear event. The drastic increase in brightness and an expanding shell of debris is the result - but the stars are not destroyed! Classical novae are believed to recur when the flow of material onto the white dwarf resumes and produces another outburst. http://www.jwestlake.com/ http://faculty.coloradomtn.edu/jwestlake/ Starship Asterisk* • APOD Discussion Page http://asterisk.apod.com/discuss_apod.php?date=130816 #APOD

APOD: M8: The Lagoon Nebula (2013 Aug 17) Image Credit & Copyright: Ignacio Diaz Bobillo Explanation: This beautiful cosmic cloud is a popular stop on telescopic tours of the constellation Sagittarius. Eighteenth century cosmic tourist Charles Messier cataloged the bright nebula as M8. Modern day astronomers recognize the Lagoon Nebula as an active stellar nursery about 5,000 light-years distant, in the direction of the center of our Milky Way Galaxy. Hot stars in the embedded open star cluster NGC 6530 power the nebular glow. Remarkable features can be traced through this sharp picture, showing off the Lagoon's filaments of glowing gas and dark dust clouds. Twisting near the center of the Lagoon, the small, bright hourglass shape is the turbulent result of extreme stellar winds and intense starlight. The alluring color view was captured with a telescope and digital camera while M8 was high in dark, rural Argentina skies. At the nebula's estimated distance, the picture spans over 60 light-years. http://www.pampaskies.com/gallery3/index.php Starship Asterisk* • APOD Discussion Page http://asterisk.apod.com/viewtopic.php?f=9&t=31932 #APOD