Today's Astronomy lesson

In local coordinates, besides 0º altitude being the (ideal) horizon, we have two other key points - the zenith at an altitute of +90º, and the nadir at -90º. These are both originally English words, though they're used less often lately. Zenith means "peak, height, best", for example "The pop star was at the zenith of her career." And nadir means "lowest, worst," as in "Brittaney Spears is at the nadir of her career."

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