Why does the night sky appear to move slowly even though the earth is rotating at 1,000mph?
In: Earth Science
Stars are blurred from the motion, when viewed from earth. We just don’t notice it much with our naked eyes because of the high temporal and low spatial resolution of the human visual system. Take a glow stick, sparkler, or flashlight and spin it very quickly in the dark. You don’t see an individual object anymore, but see instead a circular blur of light. The reason for this is that the spin rate is faster than the rate at which our eyes can discern distinct images. The distinct images of the object get smeared together in a process known as motion blur. So why don’t the stars look like spinning glow sticks? The rotation of the earth does cause the stars to spin in the sky, but the spinning is much slower. Whereas it takes the stars one day to trace out a circular path in the sky, it takes tenths of a second for the glow stick to spin in a circle. Our eyes can mostly keep up with the motion of the stars because they move slowly, but they cannot keep up with the motion of the spinning glow stick. There is still motion blur on the stars, it is just much smaller than that of the glow stick because they are moving much slower.
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