Why is Far-UV spectrum unobservable

[PianoDentist]

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 I am not sure if this is the case and I am 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!

 

[Lavabug]

I am inferring this from the literature on AGN I've read but I am by no means confident in what I am saying: I think the optical & UV comes mainly from the accretion disk, which is generally obscured by the dust torii that surround it if it's observed sideways. The jets get in the way for compact objects that are at smaller inclination angles wrt the jet axis. So I think that's why it might by difficult to resolve disk UV emission specifically from other structures like the NLR clouds.

"The physics of AGN at all scales" (Springer) might have the answer to your question.

 

[Chronos]

Earths atmosphere is extremely efficient at blocking UV light - which is good because it keeps the sun from sterilizing the surface of the earth. Life on Earth was limited to the oceans until the atmosphere became oxygenated and the ozone layer formed. To observe the universe in the UV spectrum requires space based telescopes. See http://www.britannica.com/EBchecked/topic/613577/ultraviolet-telescope for discussion.