Moon behavior.

Last Edited By Krjb Donovan
Last Updated: Mar 11, 2014 07:56 PM GMT

Question

Hello,

    For the sake of photography my question is what is the behavior of the moon relative to the sun? Such as Can I expect the moon to be X degrees east when the sun is Y degrees west?

Thanks, -Andrew

Answer

The position of the Moon changes relative to the Sun over the course of a lunation, or cycle of phases. On average, the Moon moves 12 degrees eastward per day relative to the Sun, so if the Sun is Y degrees west today, and the Moon is X degrees east today, then when the Sun is Y degrees west tomorrow, the Moon will be about X plus 12 degrees east.

The above statement is simplified, in that the motion of the Moon varies during the course of the month by as much as a degree and a half per day, compared to the average. Also, it's not clear what reference frame you are using when you say so many degrees west or east. Depending upon the coordinate system you are referring to, your latitude could also affect the angle; but no matter how you define things, whatever angular relationship the Sun and Moon have on one day will be different on other days.

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