Hi couldn't find a similar thread so thought i'd make one. I keep seeing around the web that the far-UV spectrum is unobservable (context is looking at the spectra of AGN) but no-one seems to explain why. I think that its something to do with hydrogen strongly absorbs at these wavelengths so all the dust between us and what we're looking at intercepts all the radiation at these wavelengths. But im not sure if this is the case and im not sure why hydrogen/ or interstellar dust would absorb strongly at these far UV frequencies. if anybody can explain why the far-uv is unobservable that would be greatly appreciated!