Jump to content

 

1825338873_SNRPN2021banner.jpg.68bf12c7791f26559c66cf7bce79fe3d.jpg

 

Moon + skyglow spectrum?


SteveL
 Share

Recommended Posts

Can anyone tell me what the spectrum of the moon (and associated skyglow from the moon) looks like? Am trying to determine why Ha imaging during full moon nights works, whereas OIII aparantly doesnt. Am assuming there is more blue/green in it than the dark red of Ha, but would like to see the spectrum anyway, just for curiosity's sake :D

Link to comment
Share on other sites

good question, I briefly thought about this before as well. The moon is reflecting sun light, so I would have thought that the glow would be all parts of the spectrum, unless it doesn't reflect the red end very well.

Link to comment
Share on other sites

Moon has the same spectrum as the Sun, as it reflects sunlight with nearly no absorption. Narrowband filters can work good when moon is glowing as they limit his glow greatly, and do not limit nebula emission - "extreme" boost of contrast.

Green O-III should perform as well, however green is more refracted by the atmospehere and slight ammount of light pollution can go through the filter (emission line between O-III lines). Also does O-III has the same band length as H-a filter?

Edited by riklaunim
Link to comment
Share on other sites

Guys,

Look's like you got the answer without me!

Yes it's just reflected sunlight so a very even Planck curve energy distribution.

The bandwidth of the various filters and the sensitive of the CCD will have some impact.

Link to comment
Share on other sites

Yes it's just reflected sunlight so a very even Planck curve energy distribution.

The bandwidth of the various filters and the sensitive of the CCD will have some impact.

Yes but don't forget for DSO imaging is the spectrum of the scattered skylight that is of interest, not the spectrum of the Moon. That's Rayleigh scattering, amount proportional to the inverse square of the wavelength ... so there's much less at extreme red / near IR (say 800 nm) than there is at extreme blue / near UV (say 400 nm) even if the input energy spectrum is completely flat.

As for OIII, it's in the green i.e. short wavelength relative to Ha, and at the peak of the solar / lunar spectrum whereas the intensity in Ha is falling off.

That's why you get much less interference from moon glow in Ha.

Incidentally you can use the same principle to image the Moon or planets in broad daylight - a deep red (Wratten #29) or IR pass filter will darken the blue sky background enough to make the object stand out ... in fact e.g. the Astronomik Planet Pro 742 actually works even better than a DSO Ha filter for this purpose. Not so good for DSOs because it will not transmit the Ha which you probably do want to record.

Edited by brianb
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.