What's a galactic telescope? It's a kind of telescope. So that means the word galactic is a classifier—it classifies things.
Now, what about ultraviolet? Is it a describer or a classifier? We generally think of colours as describers. You can intensify them (that car is very red), you can put and or a comma between them (a red, dusty car)... So how come we can put a classifier in front of a colour, like in galactic ultraviolet? Classifiers go after describers, right?
What's really going on here is that the colour ultraviolet, which we'd normally consider to be an adjective (specifically, a describer) is instead being treated as a noun. Again, this is something native English speakers do without thinking.
- We say: That is a red firetruck.
- We can also say: That is firetruck red.
One sentence is talking about a truck, one is talking about a colour but treating it like a thing in its own right, instead of a describer attached to a noun.
Colours are a bit weird like this!