Position of rising moon

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

Question

I have noticed that the moon rises in at least two different places and would like to know if it follows any pattern as the sun does. There doesn't seem to be a connection between the position of the sun rising and that of the moon. In the past few evenings we have seen some spectacular moon rises across the sea, north of east, here on the east facing bay where we live. In the spring the moon rose a good deal further to the east. Sometimes we have cloudy weather and then our moon tracking gets put on hold. With many thanks, Ruth

Answer

Just as the Sun moves north and south during the year, the Moon moves north and south during the month (in fact, they follow very nearly the same path, just at very different rates). So, depending upon where the Moon is in its north-south motion, it could rise well to the north or south of east, and set well to the north or south of west. On a day when it rises in the north, it will also set in the north; but a couple of weeks later, it would rise and set in the south. If you follow the Moon's rising from day to day, you would see this as a gradual change; but if clouds interrupt your observations, the rising and setting positions can seem to shift very suddenly, because of the changes that occurred during the days you couldn't make any observations.

There is a relationship between how the Moon rises and the Sun rises, but it changes during the month, as their separation changes. When the Moon is close to new, it is close to the Sun, so it rises and sets in the same part of the sky as the Sun. But when the Moon is close to full, it is opposite the Sun, so it rises and sets in the opposite way from the Sun. For example, in the winter, when the Sun rises in the south, the full Moon rises in the north; while in the summer, when the Sun rises in the north, the full Moon rises in the south.

Courtney Seligman Professor of Astronomy Long Beach City College

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