I'm an amateur astronomer and lots of things break the immersion for me. But more than anything else, this:
http://i.imgur.com/kmud7Ca.jpg
Why Frontier can't fathom that a partially-illuminated sphere is represented in two dimensions by a semicircle bounded by a semiellipse. It's basic computer programming. This breaks the immersion for me like Christopher Reeve finding the penny in his pocket in
Somewhere in Time.
http://i.imgur.com/k4hhnn9.jpg
(Talking of time, I don't believe in time dilation or relativity, I think it's the post-modern equivalent of Middle Ages quack alchemy and dogma. '
Thou shalt not travel faster than light'. But travelling faster-than-light you would certainly see wildly unusual vistas that aren't represented in
Elite, things that are actually behind you rushing away in front of you in mirror image whilst moving backwards in time. But time isn't actually changing beyond its usual forward motion one second at a time everywhere in the universe at once, the apparent reverse motion of time is just an optical illusion caused by overtaking from behind light that left your point of origin further in the past. It is interesting to consider, that whilst it is theoretically possible to move in such a way as to be able to see
backwards in time, as yet at least it is impossible to conceive of moving in such a way as to be able to see
forwards in time, into the future. But I don't expect the game to emulate any of that.)
Then I can be exploring a remote unexplored star system lost among millions of unexplored star systems 60,000 light-years from the Bubble, land on a barren virgin world, drive around for about ten seconds and then start finding evidence of human visitation what seems like every five hundred yards or so. All over the globe.
Also the holographic HUD. I hate the HUD. I think someone's girlfriend designed it. Having to roll the ship to be able to read the velocity indicator because it's mashed into something on the scanner. Or dive away from a star because its reflection on the dash is obscuring the ship's compass. Why I can't just have a regular dashboard with properly organized indicators on a black background so I can actually read them. I can't even edit the colour scheme except by hacking an .ini file, and even then it's impossible to select a preferential combination of colours. For such an accomplished game the HUD is unbelievably poor, and it really bothers me all the time I'm playing the game.
The stars are all spherical. There are no grapefruit stars, or stars swapping material, or tenuous stars like bags of cats.
The planet types are all pretty much identical, with globally identical terrain.
The layout of star systems doesn't vary much, IRL there are some wildly eccentric orbits of exotic multiple systems of up to nine stars or more looping in gigantic ellipses, sometimes with immense dust discs.
The Milky Way is bigger IRL.
There are no globular clusters.
There is no evidence of alien habitation on plainly-inhabited (by definition) ELWs (night lights).
I don't expect an astronomical simulation of course, but I really think that the planetary illumination and HUD need fixing as top priorities.