Hi Ronaldo,
1) The Orion Nebula is about 1500 light-years away from us (a mere
8.8 trillion miles), which makes it relatively close on an astronomical
scale, allowing us to study in detail its structure. The Milky Way
galaxy is about 100,000 light-years across, and so not only is Orion in
our galaxy, it is in our section of the galaxy.
2) The Orion Nebula is located in the sky very close to the
ecliptic (the plane containing the sun and the Earth's orbit), and very
close to the zero-hour marker on a sky chart (the "right-ascention").
Like everything else in the sky, it rises in the east and sets in the
west, and so it doesn't make much sense to ask if it is in an easterly
direction or a westerly direction because these directions change as
the earth turns on its axis. My guess is that the zero of right
ascention is a meridian over Greenwich observatory in England at
midnight on January 1, but I could be wrong. It's arbitary.
The center of the galaxy is estimated to be about 30,000
light-years away in the direction of Sagittarius (-25 degrees -- south,
and at a right ascention of 19 hours. 24 hours is a full circle). The
Orion nebula is in our arm of the galaxy.
3) Well, in our own frame of reference, the galaxy isn't really
going anywhere (aside from the fact that we are slowly orbiting its
center). In another galaxy's frame of reference, our galaxy may be
moving quite quickly. Nothing prevents galaxies from colliding into
each other, and in fact because they attract each other
gravitationally, it appears that galaxies have collided. Here's a nice
web site with pictures of some colliding galaxies:
http://astrowww.phys.uvic.ca/~patton/openhouse/collisions.html.
In case the site goes away, I'll include a very nice picture from it:
4) The Orion Nebula almost certainly is moving with respect to us,
but I cannot easily find a good estimate of its speed. Because it is so
close, it probably isn't moving very fast at all as we look at it,
because it is orbiting the center of the galaxy at more or less the
same speed as we are. (Quantities like this are never exactly equal,
however).
You may be asking about the Hubble law, which describes how the
average velocity of objects far away from an observer increases with
the distance. All objects in our galaxy are so close to us that their
motion around the center of the galaxy is the most important
contribution to their speed in our frame of reference. Nearby galaxies
also have their own speeds relative to each other and may collide, as
we have seen. Galaxies very far away tend to recede at velocities which
are larger for farther away galaxies, but there is also a bit of random
motion in addition to that, as galaxies move within their own local
groups.
Tom
(published on 10/22/2007)
