Why does a star appear dimmer when observed near the horizon compared to overhead?
Answer
Its light travels through a much longer column of the atmosphere.
When an astronomical object is positioned low on the horizon, the light originating from that star must traverse a substantially greater vertical distance through the Earth's atmosphere compared to when the same star is located directly overhead (at the zenith). This increased path length means the light encounters a larger quantity of air molecules, dust, and haze, resulting in significantly more light being scattered away and absorbed before reaching the telescope or eye, causing a demonstrable dimming effect known as atmospheric extinction.
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