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Young World
WORLD OF SCIECE
How bright?
DR. T. V. PADMA
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Look up at the night sky. It is aglitter with heavenly bodies.
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Photo: AP
Night sky: Sparkling young stars.
When you gaze up at the night sky, you’ll notice that some stars shine more brightly than others — not all are as resplendent as diamonds in the sky. Magnitude
Astronomers today compare the brightness of heavenly objects by how bright they appear as seen from earth. This system of classifying an object’s brightness using its apparent magnitude is based on the ratio 1: 2.512. A heavenly object with a magnitude of 1 is 2.512 times as bright as one of magnitude 2, which in turn is 2.512 times as bright as an object of magnitude 3, and so on. A star of magnitude 1 is therefore a hundred times as bright as a star of magnitude 6. Our sun is so bright that it is assigned a negative magnitude of -26.7.
So how bright is magnitude one, and why chose this brightness? And where did 2.512 come from? The magnitude system is defined such that an increase of 5 magnitude corresponds to a decrease of intensity by a factor of 100. Thus an increase of one magnitude is the fifth root of 100 (i.e. 100 = 2.5125).
Over the next few weeks, this column will be devoted to exploring some bright heavenly bodies.
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