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Physics - Formulas - Inverse Square Law

The brightness of an object decreases dramatically as we move farther from the source. The result is due to a larger "sphere" of influence. Light from a source like a star shines in all directions, to the area of illumination increases with increasing distance so the total brightness thins out.

This is called the Inverse Square Law:

If we know the distance to a star, we can use this equation to determine its brightness.

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