Atmospheric distortion of close-by looking stars. Or something like that its called - too low sources get distorted close to nothing, but close by or a bunch of them aether appear as one or makes nice halos - or the milky way. Now i dont know, if a simple "appearance distance" to each other function for this would work well, as the wavelength spectrum of the stars has some part of it too (dwarfs or neutron-ones have a large difference there and atmosphere has some play to it too - also, else wave-lenght fields need some color information - but im not sure if anyone is going to try build an IR, UV and radio-range observatories in OT - might be more actuall when inter-planetary stuff is made for satellites alike - still a thing for people like hardcore NASA staff being nerdy after work), doe, it may be of interesting result. Problem is, you need to somehow define the intensity of each star-light, but may be taken from the star-map texture pixelage. Also, if done for actual frame FOV and magnification, it may give up nicely for lens focusing effect - where, when you look whyte an telescope, this effects fades accordingly to the magnification, giving you the sharpness of it. (there is some limit due to atmosphere/space dynamics, humidity/particles in vision slope and temperature playing whyte the magnetic field motion, but setting some well set max and min on that distortion effect is all it needs for a simple approach). ...
