Are there any observations of the "end" of a Spiral Arm?
I don't think you can define the "end" of a spiral arm. Or the "edge" of the Galaxy.
I am trying to map the Foundation Milky Way, and one bit of information is that Terminus is located at the "terminus" of one Spiral Arm. I take it to mean that the Spiral Arm terminates a little away from Terminus.
What characterists can I suppose this region will have? Again, I would imagine that there would be no O,B or A stars in the vicinity of Terminus except in the direction of the Spiral Arm,
Groups of A stars have been seen in the halo of our Galaxy. These may have formed there recently due to disturbances from other nearby galaxies, or may be some of the remnants of other galaxies which have been cannibalized by the Milky Way.
The arms of a spiral are pretty well defined by the bright OB associations because such stars form there and have such short lives that they do not move far from their birthplace before they die. Long-lived stars like our Sun travel around the galaxy and are frequently found in between the spiral arms.
and that those bright stars in the Spiral Arm would be clumped together.
Not necessarily. The spiral arms can be several hundred parsecs wide in the plane of a spiral galaxy.
This would mean something like a geometry of about 90 degrees [or a little less] for the angle (Center of the Milky Way) - Terminus - (bright stars of the Spiral Arm)
Perhaps, but you wouldn't be able to actually see the central bulge from there unless you were located significantly (a kiloparsec?) above/below the plane of the galaxy, because of extinction by the intervening ISM, clouds of which concentrate close to the galactic plane.
In reality, the sky wouldn't look a whole lot different from there than it does from Earth, unless Terminus were actually some distance beyond where the spiral arm appeared to end in a visible-light photo taken from outside, in which case there might be fewer naked-eye stars all around the sky and a "Milky Way" limited to one side of the sky.
-- Ronn! :)
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