Spectrums when there's moonlight?

[Nigella Bryant]

Hi all, can you image spectrum during moonlight or does this affect the results?  Thanks for looking.

[andrew s]

Yes  you can especially with a slit spectroscope. You can subtract the "sky" background which will remove moon light, sky glow and general light pollution .

Without a slit you can still do sky subtraction it but it is not quite so effective.

Regards Andrew 

[Nigella Bryant]

4 hours ago, andrew s said:

Yes  you can especially with a slit spectroscope. You can subtract the "sky" background which will remove moon light, sky glow and general light pollution .

Without a slit you can still do sky subtraction it but it is not quite so effective.

Regards Andrew 

Thanks Andrew, that's great news, I can do something even when the moon's up. 

[robin_astro]

You can indeed do spectroscopy in bright skies but with slitless spectroscopy (eg the Star Analyser) the target does need to be brighter than with dark skies.

With a typical Star Analyser setup the spectrum brightness is about 6 magnitudes fainter than the star because the light is spread out so if you can image say a mag 12 star in bright moonlight the faintest star you could record with the Star Analyser on that night would be ~mag 6.  With dark skies if you can get to mag 20 in an image you would be able to record spectra to ~mag 14.  A slit keeps most of the sky background out  which means it is possible to record faint objects even in full moonlight or bad light pollution. I have a couple of little demonstrations of the effect of a slit on the sky background here on my website

http://www.threehillsobservatory.co.uk/astro/spectroscopy_4.htm

http://www.threehillsobservatory.co.uk/astro/spectroscopy_18.htm

[Nigella Bryant]

1 hour ago, robin_astro said:

You can indeed do spectroscopy in bright skies but with slitless spectroscopy (eg the Star Analyser) the target does need to be brighter than with dark skies.

With a typical Star Analyser setup the spectrum brightness is about 6 magnitudes fainter than the star because the light is spread out so if you can image say a mag 12 star in bright moonlight the faintest star you could record with the Star Analyser on that night would be ~mag 6.  With dark skies if you can get to mag 20 in an image you would be able to record spectra to ~mag 14.  A slit keeps most of the sky background out  which means it is possible to record faint objects even in full moonlight or bad light pollution. I have a couple of little demonstrations of the effect of a slit on the sky background here on my website

http://www.threehillsobservatory.co.uk/astro/spectroscopy_4.htm

http://www.threehillsobservatory.co.uk/astro/spectroscopy_18.htm

Thanks Robin, appreciate your input. I'd love one day to get a slit spectrograph but I'm new to this and learning the ropes with the star analyser 100, lol. If I progress well I'll consider more expensive equipment. To be honest it's great to do something scientific and eventually when I'm good enough contribute to science. I've imaged b4 but honestly don't see the point in producing, although lovely, images just to post on Facebook forum's, etc. But as they say, to each their own, lol. 

[robin_astro]

4 hours ago, Nigella Bryant said:

I'd love one day to get a slit spectrograph but I'm new to this and learning the ropes with the star analyser 100, lol. If I progress well I'll consider more expensive equipment. 

Hi Nigella,

Yep, that's exactly why I developed the Star Analyser.   (Well actually, mainly I just  wanted one for myself !  But I convinced Paton Hawksley that they might sell a few and the rest is history as they say)

Have fun !

Robin

[Nigella Bryant]

1 hour ago, robin_astro said:

Hi Nigella,

Yep, that's exactly why I developed the Star Analyser.   (Well actually, mainly I just  wanted one for myself !  But I convinced Paton Hawksley that they might sell a few and the rest is history as they say)

Have fun !

Robin

Yeah, I realised that, lol. Thanks for your ingenuity.