I Visible light Over Large Distances

[RobbyQ]

TL;DR

Visible light Over Large Distances

How does light maintain enough energy in the visible part of the spectrum for the naked eye to see in the night sky. Also, how did it start of in the visible frequency part of the spectrum. Was it, for example, photons being ejected at that frequency after high energy particle interaction. Or does the light become visible (spectrum) after hitting our atmosphere or space dust or something?

EDIT: Actually I just thought. Maybe the EM starts off as very high energy (outside the visible spectrum) But then over distance it loses energy and then becomes visisble as it's frequency reduces. Can anyone confirm

 

[Ibix]

Light from stars is emitted as visible light and reaches us as visible light (ditto the other frequencies stars emit). No energy is lost on the way except if there are dust clouds or other stuff in the way that absorbs light, but that doesn't change light into microwaves or something - it mostly just makes it dimmer.

Light from distant galaxies is redshifted in flight, but only really sensitive telescopes can see those.

 

[RobbyQ]

Light from stars is emitted as visible light and reaches us as visible light (ditto the other frequencies stars emit). No energy is lost on the way except if there are dust clouds or other stuff in the way that absorbs light, but that doesn't change light into microwaves or something - it mostly just makes it dimmer.

Light from distant galaxies is redshifted in flight, but only really sensitive telescopes can see those.

Thanks.
So I guess also that light emitted in the non visible (higher frequencies) could interact with, say, dust clouds (as you mention) and then continue their journey to the naked eye in the visible spectrum having been absorbed (lost some energy) and re-emitted as visible?

 

[Ibix]

So I guess also that light emitted in the non visible (higher frequencies) could interact with, say, dust clouds (as you mention) and then continue their journey to the naked eye in the visible spectrum having been absorbed (lost some energy) and re-emitted as visible?

Mostly it's just dimmer, not at different frequencies. There are absorption and re-emission processes, which is why things like nebulae glow at all, but if you're looking at a star (even through a dust cloud) then you're seeing the spectrum the star emits, not some shifted version of it.

 

[Ben vdP]

Essentially true; there are however some additional physical processes to take into account.

Difference in gravitational potential causes a redshift or with satellites a slight blue-shift.
A photon has to perform work to leave a star and looses energy, i.e. redder.

The star (and the galaxy it is in) can be moving in any direction this gives a classical doppler effect.

Light traveling through the universe can also loose some energy due to subtle mechanisms as inelastic or Raman scattering.
As far as I know this is normally neglected.