Starlit Sky: 2. Brightness of a star

….contd from Starlit Sky: 1. Gazing up


 

When you look up at the sky, all the stars do not shine with the same intensity. Some are very bright and some not so much. Some of them are barely visible.

The difference in the brightness between stars is measured using “apparent magnitude”. Apparent magnitude is the measure of the brightness of a celestial object as observed from Earth. The brighter the object is the lower is its magnitude. The Sun which is the brightest for us has an apparent magnitude of -27.

All the visible stars are divided into 6 categories of brightness. The brightest ones are in 1st category. The stars in the 2nd category will have a brightness 2.5 times less than category 1 stars. The 3rd category stars will have brightness 2.5 times less than ones in 2nd category and so on. The stars in the 6th category are barely visible. The 1st category stars will be 100 times more brighter than the 6th category stars.

One thing to remember here in that this brightness is an apparent measure. These are categorized based on an observer on Earth. In reality, a 6th category star may be bigger and brighter than the 1st category star. But since its distance from the Earth may be farther than the 1st category star, it “looks” more bright to an observer on Earth.

 


…to be continued…………….

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One Comment Add yours

  1. Really interesting. You have explained it in such a simple manner.

    Liked by 1 person

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