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Astronomy Picture of the Day
Posted By Editor On April 28, 2011 @ 7:39 am In Photo Essays | Comments Disabled
An ingenious and creative 10 second exposure from a swinging camera recorded these gyrating trails of the celestial pairing. Can you tell which trail belongs to the star and which to the planet?
Explanation: On June 4, 2010 Regulus, alpha star of the constellation Leo, and wandering planet Mars were at about the same apparent brightness, separated on the sky  by 1.5 degrees. An ingenious and creative 10 second exposure from a swinging camera  recorded these gyrating trails of the celestial pairing. Can you tell which trail belongs to the star and which to the planet? Hint: atmospheric turbulence causes the image of the star to scintillate  or vary in brightness and color more readily than the planet. The scintillation is more pronounced because the star is effectively a point source of light seen as a narrow bundle of light rays. Rapidly changingrefraction  due to turbulence along the line of sight affects  different colors of light by different amounts and generally produces a twinkling effect for stars . But Mars is much closer than the distant stars and an extended source of light. Though tiny, its disk is seen as a bundle of light rays that is substantially broader compared to a star’s and so, on average, less affected by small scale turbulence . The result is the varied, rainbow like trail for Regulus (left) and the steadier, consistently reddish trail for Mars.
Visit the NASA/JPL website to view more Astronomy Pictures of the Day 
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URL to article: http://www.berthoudrecorder.com/2011/04/28/astronomy-picture-of-the-day-64/
URLs in this post:
 Copyright: http://apod.nasa.gov/apod/lib/about_apod.html#srapply
 Juergen Michelberger: http://www.jmichelberger.de/
 separated on the sky: http://apod.nasa.gov/apod/ap100610.html
 a swinging camera: http://apod.nasa.gov/apod/image/1104/CamerapendularMichelbergerX.jpg
 star to scintillate: http://www.astrophys-assist.com/educate/starry/starrynight.htm
 refraction: http://www.physicsclassroom.com/class/refrn/u14l4a.cfm
 line of sight affects: http://www.scientificamerican.com/article.cfm?id=why-do-stars-twinkle
 twinkling effect for stars: http://adsabs.harvard.edu/abs/1952IrAJ....2....5E
 turbulence: http://www.islandnet.com/~see/weather/elements/twinkle.htm
 Astronomy Pictures of the Day: http://antwrp.gsfc.nasa.gov/apod/
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