In astronomy one of the biggest confusion that newcomers face when they go out for observations seems to revolve around the brightness of stars. An enthusiastic new student knows that the pole star will help him find directions since it is always north and this ‘specialty’ of the pole star probably puts a psychological fact in his head that the pole star would also be the brightest star. Psychological because this statement about pole star being the brightest star is not present in any literature and is not announced anywhere and when corrected, always draws a response saying “But I thought pole star was the brightest”.
The pole star is called that because it happens to lie almost exactly above the Earth’s north pole. Due to this, even as the Earth rotates this star appears stationary. In addition, given its position it can help observers in the northern hemisphere locate north. The ‘pole star’ is this star’s designation. Its name is Polaris. And Polaris is not the brightest but the 48th brightest star in the sky! Fairly ordinary isn’t it?
The glowing title of brightest star goes to Sirius. It lies in the constellation Canis Major, loosely translated as the Big Dog and hence Sirius is also called as the Dog Star. Incidentally the name Sirius comes from a Greek word Seirius, meaning “scorching” or really hot! At 8.5 light years, Sirius also happens to be the fifth closest star to the Sun.
After Sirius come the stars Canopus in constellation Carina, Rigel Kentaurus (or the Alpha Centauri system) in Centaurus and the fourth brightest star is Arcturus in the constellation Bootes. All these stars have negative magnitudes. Magnitude is the term used by scientists to denote the brightness of stars. According to this scale, lower the magnitude number, brighter will be the star. So the Sun is brightest at -26! In the more preferred night sky, Sirius has the brightness of about -1.5 followed by Canopus at -0.72, Rigel Kentaurus at -0.27 and Arcturus at -0.04. After this all stars have positive magnitudes.
On a perfectly clear night, with no light pollution the faintest stars we can see are around 6th magnitude. Facing north we see Pole star or Polaris at magnitude 2.0 as an ordinary and faint star.
Nikhil Pawar
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Posted on April 21, 2008
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