Just out of curiousity, what would the Milky Way look like to someone, say, 100,000 lightyears away? That's about the same distance as the diameter of the galaxy. Would it be visible to the naked eye?

Visit this site, go to manual mode, and adjust the setting to 100,000 light years away:

http://micro.magnet.fsu.edu/primer/j...su/powersof10/

Quick answer: it would not only be visible to the naked eye, it would be spectacular! At that distance it would cover about half the sky.

I'm not so sure it would be spectacular.

Sky and Telescope had a little cartoon article about this a few months back--the brightness of galaxies are pretty diffuse. They claimed that a nearby galaxy would be dim. Sorta like when we look at the Milky Way now--hey, we're closer to it now than we would be if we were outside of it.

It'd be like looking at the Magellanic clouds. Naked eye, anyway. Wait, I guess the Milky Way in a dark sky is spectacular. What am I thinking?

That's an interesting point - in an urban area, a nearby galaxy might be invisible. But it would be truly amazing to see an entire spiral in the sky in a dark sky.

Assuming that the vantage point is far enough above (or below [img]/phpBB/images/smiles/icon_biggrin.gif[/img] ) the galactic plane that the core is visable, the view would be stupendous. The spiral arms would have a a similar surface brightness to the Milky Way as seen from Earth (you would need a dark sky site to truely appreciate them). The core, on the other hand, would be awesome.

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T. Anderson

Isn't part of the Milky Way we see in the sky actually the core of the Milky Way Galaxy? Why isn't it considerably brighter or "awesome" in that direction?

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SeanF

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There are actually a lot of dust clouds in the way, aren't there?

There are dust clouds in the way from all directions. When we look at other galaxies, the core is not significantly brighter than the rest, is it?

GrapesOfWrath says:
There are dust clouds in the way from all directions. When we look at other galaxies, the core is not significantly brighter than the rest, is it?

J-Man says:
Let's vote....

<url>http://oposite.stsci.edu/pubinfo/nearbygalaxies.html</url>

My vote is that the "core" is generally brighter.

[img]/phpBB/images/smiles/icon_smile.gif[/img]

I just looked at the first couple, so my vote is no.

What do we mean by "significantly"? I guess, the question is, is it bright enough to make us impressed if we were to see it in the manner we are imagining.

For instance, here are pictures of the Large Cloud of Magellan and the Small Cloud of Magellan. In those photos the core does look brighter, but does it make that much of a difference when we look at them naked eye from 200,000 light years away?

1. If viewed from Earth: I would vote for a galaxy like the Milky Way to be spectacular from 100,000 light years away if viewed from a remote area as are the Magellanic clouds also spectacular from Earth in a very dark sky.

2. If on the other hand, the actual Milky Way were viewed from 100,000 light years away (in an unobstructed view,) without interference from a bright moon or artificial light such as an alien baseball field, I'd still vote for an impressive view. (You would tend to see more of the spiral galactic shape than we do here within it.) That doesn’t mean it wouldn’t be faint to human eyes, but it would still be impressive in a dark sky.

Chip

The Magellanic Clouds are dwarf Irregular galaxies and are not in the same brightness class as full size spirals like the Milky Way and M-31 in Andromeda.
The core of M-31 is visible to the unaided eye from over two million light years away, but the spiral arms require a large amateur 'scope two be seen clearly. If the Earth were situated above the disk of the galaxy so that the view of the core was unobstructed, the spiral arms would be similar in brightness to the Milky Way as seen from our present location, but the core would be several times brighter than the arms.

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Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson

Considering that M31 has less optical output than the Milky Way by virtue of it's larger size and lower mass and M31 is still very visible from two million light years away, then at a distance of 100,000LY, the Milky Way would be truly spectacular.
I'm estimating here, but the core would be of a magnitude well below mag. 0 and the spiral arms would also easily break through the mag. 4 required for visibility from a moderately urban location - such as where I live.

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Anyone know what the magnitude of the Milky Way is, for comparison? The point of the Sky and Telescope article was that Hollywould sometimes portrays extraterrestrial skies with dramatic views of galaxies, but the surface brightness doesn't increase that much--so the views are more like our Milky Way, rather than the popular photos of galaxies, even from close up.

Magnitude has a divisor of distance. Thus, since you are "in" the Milky Way, you can not justify a proper magnitude for the entire galaxy because you would be dividing by zero. For the same reason you can not assign a magnitude to Earth unless you are speaking in terms of some exterior reference point like the moon.

This site lists the absolute magnitude of the Milky Way at -21, and that of the small magellanic cloud as -17. That's four magnitudes, and the milky way is much bigger, right?

That site also lists the visual magnitude of the SMC as 2.2. Given this, the Milky Way would be -1.8 at 195,000 LY (brighter than Sirius). At 40,000 LY it would be nearly 24 times brighter. This is about 3.5 magnitudes.
Therefore at 40,000 LY the Milky Way would shine at -5.3 magnitude (about two and a half times brighter than Venus [img]/phpBB/images/smiles/icon_eek.gif[/img] ). Granted, it would be spread out over nearly half the sky, but most of this light would be concentrated in the core which would only occupy about 50-60 sq. degrees of the sky.
I still feel that it would be an awsome sight.

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Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson

Yes, like Chip says, it would be spectacular, of course.

The Milky Way, and the Magellanic clouds, are spectacular. The only remaining question is, would the Milky Way from outside be more spectacular than from inside?

It already stretches completely accross the sky, and we do get glimpses of its core--obscured somewhat, sure. Let me see if I can dig up that S&T...nope, can't. Someone want to come over and help me look?

From inside, the core is obscured. Just look at any wide angle shot of Saggitarius.
From outside, the core is not obscured. It will be very bright. We can see M31's core from 2,000,000LY away as a mag 3 object. Our galaxy's core is brighter than M31's is and we're only talking 100,000LY distance.

Truly spectacular.

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"We want a few mad people now. See where the sane ones have landed us!" - George Bernard Shaw

Yep, have to vote with the Truly Spectacular crowd here, unfortunately, it might be awhile before we get to see such a view for real. How long will it take the Voyagers to leave the galaxy? Or is it true to say that they never will?

Andromeda is visible in our skies with the naked eye, but only the central core can be seen clearly; so there is definitely a difference in brightness between the arms and the core.

Here is a fictional representation of the Milky way galaxy I have made using Celestia;

click on the thumbnail for a larger image. The Sun is at the centre of the graticule...

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