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A retrograde Milky Way?
Looking down on the Milky Way from the north galactic pole, our galaxy
rotates clockwise. For a planet in the solar system, the corresponding rotation would be deemed retrograde. Why was the north galactic pole defined in this way? Because it is in the northern hemisphere (i.e. has positive declination)? Were it roughly near the Earth's northern axis, or the northern axis of the solar system, then this would make sense, but since it has a declination of less than 30 degrees, I think it would be more intuitive to define it so that the rotation is prograde. |
#2
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A retrograde Milky Way?
On 3/30/2015 10:29 AM, Phillip Helbig (undress to reply) wrote:
Looking down on the Milky Way from the north galactic pole, our galaxy rotates clockwise. For a planet in the solar system, the corresponding rotation would be deemed retrograde. Why was the north galactic pole defined in this way? Because it is in the northern hemisphere (i.e. has positive declination)? Were it roughly near the Earth's northern axis, or the northern axis of the solar system, then this would make sense, but since it has a declination of less than 30 degrees, I think it would be more intuitive to define it so that the rotation is prograde. How about the magnetism? The earth's north-pole is actually the magnetic south-pole, so perhaps it was to avoid creating this inconsistency again? :-) -- Jos |
#3
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A retrograde Milky Way?
In article ,
"Phillip Helbig (undress to reply)" writes: Why was the north galactic pole defined in this way? Because it is in the northern hemisphere While I can't cite definitive evidence, I'm sure that was the reason. There is a specific IAU resolution defining the north pole of any solar system body as the pole pointing north of the invariable plane of the solar system. That's a poor definition in my opinion, but it got a majority vote. ... so that the rotation is prograde. The traditional astronomical word is "direct." "Prograde" is a neologism that no true astronomer would use. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
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