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Astronomy/Sunset at summer Solstice same location on Horizon as a full moon set on Winter Solistice?

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Expert: Jesse Martinez - 12/16/2009


Question
A friend observed this and I recently confirmed it is fairly accurate (at least for Seattle WA) with the recent full moon set on a clear night now near the winter solstice. The full moon set at dawn near where I have the seen the sun set at the summer solstice, over the Olympic Mountains NW of Seattle. There probably is a connection between the plane of the earth's orbit and plane of the moon's orbit; either a fixed angle or perhaps precession of some type?

Answer
Hi Bob. Thanks for the question. It is another head scratcher. Fortunately I love these.

The sun travels along a path in the sky called the ecliptic. The moon's orbit is inclined by 5.1 degrees to the ecliptic. When the moon is full and it sets, it could anywhere from +5.1 to -5.1 degrees off the ecliptic. This varies over time. There are about 12.37 moon cycles in an earth year, so one year from now, the moon would not set in the same place on the same specific day since its inclination will be different than it was the year before whereas the sun will, even though the two solstices are six months apart, since its path *is* the ecliptic. The point here is that at any time of year, the sun is traveling on the ecliptic, while the moon is not. That is the first reason I thought of for there being no connection between the two events in your question.

Intuitively, I know there is no connection. However, if there were exactly 12.000 months in a year, I would be "inclined" to think it was possible or even true. But that is not the case. I do believe there are other reasons why the relationship between these two events was a coincidence and not a rule, but I can't think of any right now. Nor do I think it is the only factor involved in this scenario. I will update the answer if something else comes to mind.

So there you are. My shoot from the hip answer to this question. I hope this helps. In the meantime, here is a site I am going to be looking over. Maybe you should too.

Jesse

http://en.wikipedia.org/wiki/Orbit_of_the_Moon

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Jesse Martinez

Expertise

General and specific questions about the solar system and stellar and galactic astronomy, are what I can easily answer off the top of my head. For example, what is the largest planet in the solar system? How far away is the moon? Have there been any confirmed planets in orbit around stars other than the sun? How many stars are there? The tougher ones like explaining the big bang theory and black holes I will leave to the PhD’s. Even though I could muster an answer, I would have to research it more than I would like. I would also like to answer questions that involve Astronomy with other sciences, chemistry, biology, physics, geology and mathematics as long as they are not PhD level.

Experience

I have been into astronomy since I was 8 years old. I have kept detailed journals of my observations through small telescopes. Over the years I have participated in amateur observation projects for organizations like ALPO. My personal research has involved "discovering" the moons of Jupiter with a 4½-inch Newtonian reflector without any outside information like charts and tables. In a summer long project, I determined the existence of and plotted the orbits of the four major moons of Jupiter. From these observations, my data on orbital elements was surprisingly accurate (orbital radius and orbital period).

Education/Credentials
80 hours of college credits while studying physics and geophysics. Completed correspondence photography course while in high school. Took two semesters of electronics training at a community college. Studied computers and graduated from a technical school at the turn of the millennium, gaining A+ and Microsoft Certified Professional credentials. Hablo Español. Si quieres preguntar en Español, estoy a su servicio.

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