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Does the moon remain at a constant distance from earth? If so, then why does the moon appear larger at the horizon, when it would actually be further away from our viewpoint? And, if the moon does _not_ keep a consistent distance from the earth, then why does the moon appear so large at the horizon anyway?

Variations in distance too the Moon over a day are not appreciable enough to cause any change in the size. Moon appears big near the horizon because you have things to compare it with, like a distant building and so on. Next time, do an experiment. Try to measure the angle subtended by the Moon by keeping a coin or nail at an arms' length between you and the Moon. Measure the size when the Moon is near the horizon and when it is high in the sky, nearer Zenith. Compare two sizes.


The apogee and perigee of the moon's orbit are 356400 and 406700 km respectively, a variation of about 10% around the mean value of 384400 km. Of course, it takes 2 weeks for the moon to move from apogee to perigee. (extra credit: why?)

John Hawley

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