What physical law governs how the intensity of starlight drops dramatically as it travels vast distances to Earth?

Answer

The inverse square law

The intensity of light from a distant source diminishes according to the inverse square law as it traverses space. This physical relationship dictates that if the distance to a light source is doubled, the apparent brightness that reaches the observer decreases to one-fourth (1/2 squared) of its original intensity. Because stars are extremely far away, this continuous drop-off means that even intrinsically brilliant stars arrive at Earth as very dim photons. This effect is a fundamental principle explaining why distant celestial objects inherently appear faint, setting the baseline challenge before atmospheric or artificial interference is even considered.

What physical law governs how the intensity of starlight drops dramatically as it travels vast distances to Earth?

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