Do you know how to measure the brightness of the stars? Actually, the brightness of a star is measured in terms of its ‘magnitude’. Before the invention of the telescope, stars were grouped by what we would today call their apparent magnitude –that is, their brightness as seen from the earth. The brightest stars were said to be first magnitude. The next brightest second magnitude, and the dimmest that can be seen with the naked eye sixth magnitude. This scheme was retained by astronomers even after the invention of the telescope.
It is fascinating fact to mention that stars actually tend to be grouped together in the sky. About two-thirds of all the stars you see in double-star systems- that is, systems of two stars in orbit around each other, in addition, the galaxy has many large clusters of stars, ranging in size from hundreds to millions of stars each. What a big number that is.
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