# Would a galaxy be visible from outside, but nearby?

We all know the typical sci-fi image of a guy standing on the ship deck and able to see a full galaxy. If you somehow were able to stand a few lightyears away from a galaxy would you be able to see it in full, as in the image below?

• I always thought this was a protostar or early solar system. – Burgi Mar 29 '19 at 11:20
• Do you mean whether the disk would be too faint to see because of the brightness of the center, or whether the size would fit in the field of view? – stackzebra Mar 29 '19 at 11:28
• @Burgi yes, until now I realize that is indeed a protostar, tbh I was a child when I watched that episode and looked a galaxy to me. But I have been wrong. – eli.rodriguez Mar 29 '19 at 15:26
• It might have been "tweaked" in the special editions – Burgi Mar 29 '19 at 15:32
• @Burgi, the canon is inconsistent. – Harry Johnston Mar 30 '19 at 5:15

I am very deliberately not illustrating this answer with an image, because essentially any photographic image will misrepresent what you can see in the sky with the naked eye.

The surface brightness, that is the light per unit angular area, of extended objects is independent of distance$$^1$$. This is because the angle subtended by an object is proportional to the square of its distance, and so is the amount of light reaching an observer.

In other words, a galaxy looks about the same at any distance: it gets bigger or smaller, but its surface brightness (and therefore contrast with the background sky) doesn't change. This breaks down once you get close enough to pick out the individual stars, but with the naked eye you need to be just about inside the galaxy for that to happen$$^2$$.

Now the answer should be obvious: you would never see a galaxy looking like the one in your Star Wars screenshot. Rather, it would look like other galaxies you can see in the sky. If you've been to the Southern hemisphere and seen the Magellenic Clouds, you have a good idea of what another galaxy looks like with the naked eye. Likewise if you've managed to pick out Andromeda from somewhere dark. Actually, the fuzzy band of our own Milky Way also gives a decent idea of how bright on the sky a galaxy would look from outside$$^3$$.

$$^1$$ This isn't true for really distant objects when cosmological surface brightness dimming starts to kick in, but that isn't the case here.

$$^2$$ You could pick out some individual very bright stars from further away, but the majority that make up the smooth looking light of the galaxy start to blend together pretty quickly with distance.

$$^3$$ Because we're inside the galactic disc there's a lot of dust to get in the way of the view which causes some dimming, but it still gives a decent idea.

• That said, the Milky Way is very bright on the sky if you're dark adapted and in a place with no light pollution. Obviously, it wouldn't be visible (without some visual enhancements) in a brightly lit room. – Luaan Mar 29 '19 at 9:04
• @Luaan Under good conditions, the Milky Way & Magellanic clouds are certainly bright enough to be impressive, but saying they're very bright is an exaggeration, IMHO. FWIW, I live in the southern hemisphere, and have lived in areas of low light pollution. A few years ago we had zero light pollution for a couple of days after a big storm knocked out the electricity distribution in our district. The Milky Way & Magellanic clouds looked better than ever. :) – PM 2Ring Mar 29 '19 at 9:19
• Nice answer: Realistically, the characters in the movie should not be able to see any stars at all when they look out that window. At least, not unless their eyes work very differently from ours. – Solomon Slow Mar 29 '19 at 19:21
• @SolomonSlow perhaps their AR TV is really dusty? – John Dvorak Mar 30 '19 at 10:45

From NASA:

Explanation: The Great Spiral Galaxy in Andromeda (aka M31), a mere 2.5 million light-years distant, is the closest large spiral to our own Milky Way. Andromeda is visible to the unaided eye as a small, faint, fuzzy patch, but because its surface brightness is so low, casual skygazers can't appreciate the galaxy's impressive extent in planet Earth's sky. This entertaining composite image compares the angular size of the nearby galaxy to a brighter, more familiar celestial sight. In it, a deep exposure of Andromeda, tracing beautiful blue star clusters in spiral arms far beyond the bright yellow core, is combined with a typical view of a nearly full Moon. Shown at the same angular scale, the Moon covers about 1/2 degree on the sky, while the galaxy is clearly several times that size. The deep Andromeda exposure also includes two bright satellite galaxies, M32 and M110 (bottom).

• Don't upvote this - instead write a letter to your rep about NASA funding cuts. – Keith McClary Mar 29 '19 at 4:34
• So I deduce from the NASA explanation that indeed you would be able to watch the Galaxy as in the picture but not as bright as it appears in the films. – eli.rodriguez Mar 29 '19 at 5:31
• @eli.rodriguez I can see Andromeda with binoculars - just the bright centre blob. Some can see it naked-eye. If you were ten times closer and turned off the lights in the control room and waited for your eyes to become dark-adapted, it would look about that size but not as bright. But still spectacular. – Keith McClary Mar 29 '19 at 6:03
• Andromeda has an apparent magnitude of 3.44 and the moon has -12.6, so the brightness of Andromeda is greatly exaggerated in the NASA image. – Keith McClary Mar 29 '19 at 6:44
• This doesn't answer the question at all, and in fact is grossly misleading with the image, where the surface brightness of Andromeda relative to the Moon is greatly exaggerated. – Kyle Oman Mar 29 '19 at 8:50

Standing one or two light-years would never do it. Length of our Galaxy is about 100,000 light years. In the shown picture, the visual angle would be about 15°. Do the math, they're about 380,000 light-years away from our Galaxy.

• Really like the math, but now what about the brightness? Would a photo from 380,000 light-years away from our Galaxy. would look as bright as in Sci-Fi film (without long exposure) – eli.rodriguez Mar 29 '19 at 5:34
• @eli.rodriguez It would definitely be far brighter than the background stars you see in the picture; however, I'd definitely turn the lights off in the room :) Also, it should be noted that the Star Wars galaxy is much bigger and denser than the Milky Way or Andromeda, so I'd expect you'd need to be more like a million light years away. – Luaan Mar 29 '19 at 8:59
• Just noting that they're not looking at our galaxy, as their story takes place "in a galaxy far, far away". – Doug Warren Mar 29 '19 at 15:04
• then what about standing as far away from the galaxy as the galaxy is wide? Because that was seemingly the true intent of the question, even if the exact values were off. – vsz Mar 30 '19 at 11:02