James Goss Asks: Does the Milky Way rotate and/or revolve clockwise or counterclockwise? Since we rotate around our Sun, which way are the overhead skies rotating? I somewhat understand the Ecliptic, but I’m trying to get a conceptual idea of motion; that is, as an observer on Earth, how should I think about–or orient myself to think about–which direction all these spheres and constellations are going in?

James: There are actually several questions here. First about the Galaxy called MilkyWay. All you see with your naked eyes apart of the Andromeda Galaxy and the two Magellanic Clouds (Southern Hemisphere) are inside the Milky Way. Weather it rotates clockwise or counter-clockwise it depends on how you could look at it. In space there is no up or down. The MilkyWay rotates in the direction in which the arms trail the rotation movement. 


Also keep in mind the solar system’s ecliptic plane is not in the same general plane of the Galaxy. They are tilted aproximately 60 degrees. This iage shows aproximately how our Solar System and our Galaxy are located respectiely.

Ecliptic vs Galactic Plane

Now imagine you are standing on Earth at the equator lets say in Quito, Ecuador. If north is “UP” then your body is paralel to the ecliptic so as you look UP and extend your arms east-west, in that plane is aproximately where the ecliptic is located and all planets and Sun and Moon are on or aproximately on the ecliptic. We say aproximately because Earth is tilted and the planets are not “exactly” rotating around the SUN on the ecliptic but very close to it. There is an amazing set of simulations in this page:  http://astro.unl.edu/animationsLinks.html  under the line Coordinates and Motions look for the simulation called Ecliptic (Zodiac) Simulator. It can show you exactly what constellations of the Zodiac are visible in different months and how the Sun moves through these constellations. Hope this helps. There are also dozens of good apps for smartphones available to help you determine what is visible on any given night. Keep looking up!!

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