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Pop cult sci-fi movies like to show nebulae as they appear in photographs, but to a live, real-time viewer: these dazzling, snazzy and amazing backdrops to spaceship flying in front of them in real-time live action 30 fps footage. But anyone with a real astronomy background knows that real nebulae aren't like that. They're dim. They have a low surface brightness, to be more exact, which means that even if you were close to them, you would still see little and, for very faint ones, nothing, because distance does not affect surface brightness.

This is best demonstrated by seeing how that a suitably-long exposure photograph, made of even the night sky around Earth, with no telescope, can capture some phenomenal nebulae that we just don't see at all with our eyes, just because they're just too darn dim. The Rosette Nebula is a great example:

https://www.reddit.com/r/space/comments/qouns6/rosette_nebula_setting_over_mt_whitney_california/

look at that angular size! Yet you never notice it at night, because your eyes just don't have the sensitivity.

When I first heard of this, and then had it hammered home hard with the above pic much more recently, it was a real downer, and I'm sure others here can relate.

Yet, it's also clear not all nebulae have the same equally dim surface brightness, otherwise one would need to use equally long exposures, with general equipment, to see them (given that telescopes don't increase surface brightness).

But how much surface brightness can a nebula get? Can it get enough that, even while it may not look "movie good" to our eyes, were you there close enough it took up a significant angular size on your view sphere, it'd be bright enough to be readily noticeable at a glance along with the background of naked-eye stars? (I'm presuming you're inside a galactic disc for this.)

A perhaps related question is - could a nebula like Rosette be seen, even if not with our eyes, then at least still in real time with a camera of suitably-good sensitivity? Or does the photonic nature of light prevent there from ever being enough photons present in 1/30, 1/24, or 1/15 of a second to see it, at least without an absurdly large aperture connected to the camera (and how much aperture can one add before magnification causes too much loss of FOV)? I.e. to what extent can we "reinterpret" those pop movies as just being imaginarily shot with special super sensitive cameras even if that might not account for other aspects of the VFX?

Are there any spots in the real-life universe where that, in theory, at least with a sensitive but physically reasonable color camera (i.e. small enough that it could be manipulated by a human without powered mechanical aid[*]), something approximating pop sci-fi starship scenes with gorgeous nebulosity in the background while the ship is coasting by at a modest relative speed, could be shot?


[*] NB. I realize this could require some interpretation. You naturally cannot translate your body in space without some form of powered aid because of conservation of momentum, e.g. small rockets attached to your space suit. You can, however, reorient it with suitable twisting. Given that, I am also going to say it can be qualified to "without powered aid that has significantly more force than your muscles and deliverable potential energy than your last meal". Really, what I'm trying to say is "something the size of Hubble or JWST is too big" and what I'm "really really" trying to say is "something about the size of a terrestrial-based videographer's camera and no bigger than a typical studio camera". :D

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  • $\begingroup$ Note that surface brightness is independent of distance. $\endgroup$
    – ProfRob
    Jul 13 at 5:51
  • $\begingroup$ This could easily be done in CGI, but using the real physical parameters of a nebula! I once did a nebula in blender, but I did not pay attention to it being physically accurate, just visually similar to reference pictures. I ought to try this sometimes! $\endgroup$
    – Prallax
    Jul 13 at 5:56
  • $\begingroup$ @ProfRob: Indeed, that's exactly the whole point, so what I am asking is what range of surface brightnesses exist, and whether any of them would be high enough to look movie-good with a suitably capable and equipped camera running in real time that is also not awkwardly enormous by virtue of having a ginormous objective :D $\endgroup$ Jul 13 at 6:48
  • $\begingroup$ (If you want more accurate/simple to understand parameters on that camera, a 6 inch objective is okay, a JWST is NOT okay :) If an astronaut could not hold it and point/slew it with just their hands and the puff puff maneuvering rockets on their suit with most of the dexterity expected of a cinematographer, it's not okay.) $\endgroup$ Jul 13 at 6:55
  • $\begingroup$ You just need to go fast. That'll increase the rate you receive the photons. It will also blue-shift them, making them more energetic. Ok, that will distort the colour, and shift some of the visible photons into the ultraviolet, and near-infrared into the visible. It'll also distort the shape, due to relativistic beaming. (But I guess this doesn't really answer your question, which is why I'm posting it as a comment rather than as an actual answer). $\endgroup$
    – PM 2Ring
    Jul 13 at 8:42

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