|Moonrise in San Francisco|
Before we dive into the specific factors, let's review the basics. The moon, like the sun, rises in the east and sets in the west, but of course the precise point of sunrise varies throughout the year. The sun rises either north of east in the summer when the days are longer, or south of east in the winter when the days are shorter. The full moon, which Scott was observing when he sketched the images last month, has an opposite behavior compared to the sun ... that is, the moon is in the opposite part of the sky compared to the sun and as such, in the winter the moon rises north of east (when the full moon nights are longer) and south of east in the summer (when the full moon nights are shorter).
In addition to that macro change in the position of the moonrise compared to sunrise throughout a year, there are daily changes to the position of the moonrise. The moon, being much closer to Earth than the sun, moves rapidly in its 29 day orbit around the Earth and from one day to the next is approximately 12 degrees further eastward in comparison to its location the night before. That is the main reason that a rising moon rises approximately one hour later each evening, and the primary factor that is illustrated in the drawing above. The Earth has to turn more to get to the place where the moon has moved, in this case from 8:00 pm to 9:00 pm/.
|Moonrise position changing|
There is a third factor for the change in the location of moonrise on consecutive nights which is based on the moon's orbital inclination, but that requires fairly expert knowledge of celestial mechanics to fully comprehend so we will save that for another time ... or a star party.
Today is the full moon, March 9th, 2020. You can try to reproduce Scott's experiment now, looking closely at the eastern horizon and locating landmarks where you can spot the moonrise on consecutive evenings. For the next 3 or 4 evenings the moon will rise about an hour later each evening, and also will rise at a point further to the south of east compared to the night before.
I wish you clear skies and happy viewing.