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I am building a habitable Earth like planet, but instead of it being in a solar system it is inside a Nebula.

The actual composition of the Nebula is uncertain at this point.

I am thinking the planet still needs one or more stars (that are also in a nebula) to provide it with light and energy.

I am curious about the many possibilities this could give me:

  • What would the sky on such a planet look like?

I am guessing that the nebula would be clearly visible during night time, but would it still be visible during the day? Would the blue sky block out the nebula in a similar way that it blocks out the stars?

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  • $\begingroup$ Does the sky have to be blue? See why the sky is blue; also over here. $\endgroup$
    – user
    Dec 2, 2014 at 12:25
  • $\begingroup$ The sky can be any colour that makes sense - I am just wondering if the daylight would be strong enough to block out the nebula in the same way that daylight blocks out the stars we see at night. $\endgroup$
    – Jimmery
    Dec 2, 2014 at 12:27
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    $\begingroup$ There are different types of nebula I think you'll have to be more specific to get a good answer. $\endgroup$
    – asawyer
    Dec 2, 2014 at 13:53
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    $\begingroup$ Warcraft's Outland world is inside a nebula, albeit a pretty fantasy-y one: fc02.deviantart.net/fs31/i/2008/194/2/8/… $\endgroup$
    – Kroltan
    Dec 3, 2014 at 12:33
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    $\begingroup$ Douglas Adams's planet Krikkit is surrounded by a dust cloud leaving their sky completely black. When they discover the existence of an outside universe, how many people die? "Two grillion, m'lud." $\endgroup$
    – Simon Woodside
    Dec 6, 2014 at 8:26

2 Answers 2

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The January 2003 issue of Astronomy had an article "Under Alien Skies" that investigated what the sky would look like from the surface of planets in multiple locations, including inside a nebular.

There is a making-of article here: http://www.badastronomy.com/media/inprint/underalienskies.html

It starts with the bad (boring) news:

I immediately ran into a problem. Although the nebula is bright enough to be seen by the unaided eye even from 1500 light years away, I quickly realized that from up close it would be invisible! This shocked me, but I knew I was right. The problem is that the gas is almost transparent, what astronomers call "optically thin". It glows because it is energized by the flood of ultraviolet light from the Trapezium stars.But since the nebula is transparent, we see light from every atom of it all at the same time; the light from atoms on the far side of the nebula comes right through the gas. That means that the light we see is all the light there is from the nebula.

But then gets to the good news:

"The light from the thin gas would get spread out, but there are narrow shocked filaments all through the nebula. Those are small, and they'd still be bright.".

"So, " I replied, "the sky would be filled with a web of ghostly green tendrils?" He nodded. "Yep."

And the interesting news:

Then, disaster. Jeff Hester called back... and said everything I wrote about the Orion Nebula was wrong. Gulp! He said it would be accurate for a nebula that is just rarified gas, but the Orion Nebula is far more than that. It's actually part of a much larger thick molecular cloud. This cold cloud of gas and dust is completely opaque to visible light. The Trapezium stars formed in it, and they are so hot that soon after they switched on, their heat and UV light started carving a cavity in the cloud. They were near the edge of the cloud, and eventually ate their way out to the edge. The cloud blows out from there, allowing us to see in.

But those stars also illuminate the thick gas in the molecular cloud. Since this gas is thick, from up close it would still be bright!

The original article had images to accompany it, although they don't seem to be easily found online.

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  • $\begingroup$ I understood Tim B to be saying that nebula may not glow in visible light, so their visibility, asuming that you were close enough to observe it would depend upon your senses - whether you were a person or a cat, or a fish. $\endgroup$
    – J Griffiths
    May 8, 2017 at 23:08
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The reason we don't see stars during the day is not because the Sun is too bright, but because the blue light in sunlight is scattered by Rayleigh Scattering. This means that it appears to come from all directions at once.

If this effect wasn't present then only the sky immediately adjacent to the sun would be bright and the rest of the sky would be dark enough to see the stars.

So, if you assume that your planet's atmosphere has the same properties as Earth's then unless your nebula were bright (as bright as the Moon, which is visible during the day) I don't think you would see it. Having said that, you can see Mars, Jupiter and Venus at dawn and dusk when there is still some sunlight to scatter.

So, you'd see more the nebula if there was less/no scattering of the sunlight or if the nebula were about as bright or brighter than the Moon.

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  • $\begingroup$ Very interesting, can you confirm if I've understood it right? In simple terms the materials the light interact with and the way it does affect how we perceive it? $\endgroup$
    – MVCDS
    Dec 2, 2014 at 18:39
  • $\begingroup$ It has as much to do with the gas as it does the light source. A red giant would produce a very different sky, because of the lack of blue light the stars might be visible while still providing equal heat. If you have a dense dust nebula, you would have a lot of shooting stars (most are the size of grains of sand) and you would have high dust accumulation, less dense gas nebula wouldn't have these issues. $\endgroup$
    – Quaternion
    May 8, 2017 at 23:31

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