View Full Version : Galactic disc

04-26-2016, 12:55 AM
Imagine you're stood on a rogue world, flung out into the dark depths of intergalactic space. The air is thin, the sky clear, and the dome of the sky is filled with the flat disk of the milky way. The galactic core directly above, the spiral arms stretch down toward, but never reaching, the horizon in all directions, as the cold dead world spins underfoot.

Is that realistic? Or are individual stars at that distance too feeble to perceive individually with the naked eye?

The light and cloudy band of the milky way is barely visible in my part of the world, even in the hills away from the towns and roads. I imagine my vision for this fictional world falls short of the science. Is this right?

What might you see from the space halfway between. Galaxies?

Dennis E. Taylor
04-26-2016, 01:25 AM
Have a look at the Andromeda Galaxy. You'll need to look up where it is, then you'll probably have to be out of town in a really dark sky, and even then, with the naked eye, it's just a smudge. That's at 2.5 MLy. It has an apparent magnitude of 3.44, which is well above the "standard" lower limit of 6 for visible objects, but most visible objects are point sources, not smudges.

OTOH, if you are just outside the galaxy instead of "halfway between galaxies", then what you would see would be very similar in brightness to what we see at night of the milky way. Depending on whether you were on the same plane of the galaxy or some angle above the plane, you'd see an entirely different view. in fact, if you were more than maybe 20 to 30 degrees off the plane, you'd get a good line-of-sight on the core, which would be significantly brighter. Maybe up to half the brightness of a full moon, depending on distance and angle.

I will say, though, that having that hanging in the sky would have resulted in a significantly different set of supernatural beliefs.

04-26-2016, 01:40 AM
Thanks Angry Guy. I've got dark sky camping on the to do list this year for this reason.

I don't think halfway point between galaxies is right. Just far enough that the disk fills the sky. A bit of trig will give me the distance, but that didn't occur before now.

With you on the supernatural beliefs, but this is a dead dead world.

04-26-2016, 10:58 PM
The outer edge of any galaxy is pretty hard to define. And there are likely a few straggler stars lying at a far distance from the main galactic concentration. But, as a reader, I wouldn't be very concerned about specifics of such stuff. Just describe what is visible in the sky, and let it go at that. Your story itself, what the characters do and why, is much more significant.