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I live in the Pacific North West (Washington State, US). I have watched the skies for years, looking for constellations that I recognize and keeping track of them. One of them is Orion. As I have watched Orion I noticed that it travels East to West as I look to the south. It traverses the line that is the Milkey Way...

My question is. If the stars that make up the constellation of Orion move East to West from my position, looking up and South. Why does the Milky Way seem to stay in the same position? How is it that the stars that make up Orion move but the stars that make up the milky way appear to be fixed?

Thank you in advance for any input.

Makoa
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  • For this kind of questions and curiosities there are plenty applications for smartphones as well packages and programs for PC. Perhaps they might be not accurate for professionals, but I can tell you you can have a virtual seeing of things like this. – Alchimista Feb 18 '18 at 19:29

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The Milky Way consists of numerous faint stars near our galactic equator. Many of these are visible in binoculars. As time lapse videos show, they move across the sky along with the bright stars. The light and dark patches in those digital images are easier to see visually near the galactic center in Sagittarius than in the opposite direction near Orion.

Due to its oblique angle, the galactic equator appears to go through a special cycle as everything revolves around the celestial pole. From mid-northern terrestrial latitudes, it runs overhead NW-SE when Orion is highest, low in the north when Virgo and the Big Dipper are highest, and overhead NE-SW when Cygnus is highest. We see no more than half of this cycle on any given night, which may explain the illusion you perceived.

Mike G
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    A timelapse is great way to demonstrate this! I found one with orion and the milky way both visible https://vimeo.com/205750804 – James K Feb 18 '18 at 20:10
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The East to West motion of the stars of Orion is due to the rotation of the Earth.

The Milky Way also moves across the sky during the night for exactly the same reason.

The stars that form Orion do not transverse the milky way. They remain in exactly the same position relative to the Milky Way. You are simply mistaken in thinking that the Milky way remains in the same position.

James K
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