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Earthsky Tonight—March 10: Is Sirius the most luminous star in the sky?
Posted By Gary Wamsley On March 9, 2010 @ 4:55 am In Earth & Sky | Comments Disabled
Courtesy of EarthSky
A Clear Voice for Science
Look south at nightfall and early evening, and you can’t miss Sirius , the brightest star in the nighttime sky. Mia asks, “Isn’t there a brighter star in absolute magnitude which appears dimmer because of its distance?”
Yes, Mia, you are right. Sirius looks extraordinarily bright in Earth’s sky because it is only 8.6 light-years  away. Many stars on the sky’s dome are intrinsically more luminous than Sirius, but appear fainter because they lie farther away. Apparent visual magnitude refers to a star’s brightness as seen by the eye from Earth and absolute visual magnitude measures the star’s brightness as it would appear to the eye at 32.6 light-years away.
At least three stars in the constellation Canis Major are thought to be thousands of times more luminous than Sirius: Aludra, Wezen and Omicron 2. Although the distances to these faraway stars are not known with precision, Aludra and Omicron 2 reside an estimated 3,000 light-years distant, and Wezen at 2,000 light-years.
At 32.6 light-years away, our sun would barely be visible as a speck of light, but Aludra, Wezen and Omicron 2 would outshine Sirius by some one hundred to two hundred times. At 32.6 light-years, Sirius would be about the same brightness as the Gemini star Castor .
Written by Bruce Mcclure
Space Com 
Amazing Space 
Scope City 
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URLs in this post:
 www.EarthSky.org: http://www.EarthSky.org
 Image: http://www.berthoudrecorder.com/wp-content/uploads/2010/03/10mar10_430.jpg
 Sirius: http://earthsky.org/tonightpost/brightest-stars/sirius-the-brightest-star
 light-years: http://earthsky.org/tonightpost/astronomy-essentials/how-far-is-a-light-year
 Castor: http://earthsky.org/tonightpost/brightest-stars/best-castor-brightest-second-magnitude-star
 The Stellar Magnitude System by Alan M. MacRobert: http://www.skyandtelescope.com/howto/basics/Stellar_Magnitude_System.html
 Sky and Telescope: http://www.skyandtelescope.com/observing/ataglance/
 National Geographic: http://news.nationalgeographic.com/news/
 Space Com: http://www.space.com/nightsky/
 Amazing Space: http://amazing-space.stsci.edu/tonights_sky/
 The York County Astronomical Society: http://www.ycas.org/tonights_sky.htm
 Scope City: http://www.scopecity.net/
 James S McDonnell Planitarium: http://www.slsc.org/WhatToDo/Planetarium/NightSkyUpdate.aspx
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