Alcove72 wrote:"Amateur asternaut" would be above my rank! Could someone indicate which direction our Milky Way is rotating in this view? It would be tempting to guess that we are rotating toward the blue side; but I cannot readily confirm this. IF we are rotating toward the green side, that would seem very curious.
Good question, which should be answered by someone more mathematically adept than I am.
However, I guess we should start in the middle. The little black dot in the middle of this map might just be the center of the Milky Way. From the location of this black dot, the blue disk to the right of it appears to be approaching, and the green disk to the left of it appears to be receding.
But what about the broad bright disk fragments outside the inner disk, whose rotation appears to be inverted?
Consider this picture of a torus. The Milky Way is not a torus, but to us, it looks like a flat band across the sky. But from any vantage point, we can only see a part of it. At any one time, we can't see all the of Milky Way that is observable from the Earth. At any given time of the year, only parts of the Milky Way are visible from any part of the Earth.
I think today's APOD can be thought of as a torus or a circle that has been "cut it up at the back" and spread out to allow us to see all of the Milky Way that is ever observable from the Earth. This makes the Milky way look elongated. The map has given the Milky Way a shape that it doesn't have, just so that we can "see it".
Today's map obviously doesn't show us the part of the Milky Way that is permanently hidden from us. Nevertheless and in some way, the image of the Milky Way has been "cut up and spread out", so that its apparent rotation curve has been inverted.
At least that is what I think.
Ann
[quote="Alcove72"]"Amateur asternaut" would be above my rank! Could someone indicate which direction our Milky Way is rotating in this view? It would be tempting to guess that we are rotating toward the blue side; but I cannot readily confirm this. IF we are rotating toward the green side, that would seem very curious.[/quote]
Good question, which should be answered by someone more mathematically adept than I am.
However, I guess we should start in the middle. The little black dot in the middle of this map might just be the center of the Milky Way. From the location of this black dot, the blue disk to the right of it appears to be approaching, and the green disk to the left of it appears to be receding.
But what about the broad bright disk fragments outside the inner disk, whose rotation appears to be inverted?
[float=left][img]http://hi.gher.space/dl/CPQN2Q0140HMRGY9CJ7C2JX3XF[/img][/float] Consider this picture of a torus. The Milky Way is not a torus, but to us, it looks like a flat band across the sky. But from any vantage point, we can only see a part of it. At any one time, we can't see all the of Milky Way that is observable from the Earth. At any given time of the year, only parts of the Milky Way are visible from any part of the Earth.
I think today's APOD can be thought of as a torus or a circle that has been "cut it up at the back" and spread out to allow us to see all of the Milky Way that is ever observable from the Earth. This makes the Milky way look elongated. The map has given the Milky Way a shape that it doesn't have, just so that we can "see it".
Today's map obviously doesn't show us the part of the Milky Way that is permanently hidden from us. Nevertheless and in some way, the image of the Milky Way has been "cut up and spread out", so that its apparent rotation curve has been inverted.
At least that is what I think.
Ann