refers to the relative brightness of stars in the sky.In general, it also refers to the "apparent magnitude", is to see the brightness of the stars from the earth.
the first set by the Greek astronomer xi pachacutec,, he will be a total of 1025 stars in the sky, the 20 stars as the first one of the most bright stars, and the brightness is only about half of the stars to be classed as second-class star, to the dark sixth magnitude, is almost to the naked eye can see the limit of the dark star.
this classification in the 2nd century AD, by another astronomer Ptolemy published (Ptolemy), included in the quite important works - Almagest (Almagest) in the book.
in the 16th century, Danish astronomer tycho (TychoBrahe) further "the size of the stars" as the stars of the brightness of the classification, the greater the brighter the stars look.
when the telescope was invented, astronomers is to carefully measure the size of the stars to represent its brightness difference.So until the 19th century, the brightness of the stars are still in their "it seems that the size of the" to distinguish between magnitude.
in 1856, English astronomer posen (Norman r. Pogson) found that when using the telescope to observe stars, the greater the telescope, you can see, the dark star.If he will telescope part open cover, dark stars will disappear from view.So he will cover the opening of the telescope, bit by bit the brightness of the comparison between the stars and the star.He found that magnitude difference of five stars, such as brightness are roughly 100 times, he suggested the brightness difference between each magnitude, defined as 1/5 of the power of 100, which is 2.512 times.
but 1 to 6 magnitude cannot describe was found in all the brightness of the object, astronomers extending original level ─ ─ introduce the concept of "negative magnitude".So the apparent magnitude system has been in use today.
图片：维基百科 作者：望天 编辑：虫虫
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