The distance to such an object can be worked out by comparing its apparent brightness with its known, absolute brightness.

经过比较表观亮度和已知的绝对亮度，即可得出该天体和我们的距离。

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V4, where the light reflected from a surface is compared with that reflected from surrounding surfaces, in order to control for relative rather than absolute brightness.

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It is similar to a Hertzsprung-Russell (HR) diagram but the latter plots luminosity (or absolute magnitude) rather than just apparent brightness and a knowledge of the distances of the stars plotted is also needed.

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