Effect of full moon on nebula observing through UHC filter

[RobH2020]

Hi all,

I had first light on Saturday with both my new 8" dob (upgrade from 6") and my Astronomik UHC filter.

The moon was very bright, it's getting on towards being full. 

I was wondering, to what extent would the moonlight affect my view of the Orion nebula? I understand the UHC filter should filter out a lot of the light from the moon. But I think the wavelengths that the filter lets through are also heavily represented in the moonlight's radiance...

I also guess the presence of the moonlight would mean that my eyes could not fully adapt to the dark, because it wasn't as dark as it could be.

For reference I'm in a "bright suburban" type location (red/orange boundary, in the home counties around London).

For what it's worth, I was impressed with the upgrade, but it's true what people say - the difference between an 8" scope and a 6" scope is much much less than between a 6" scope and no scope at all!

But my question is - should I expect to see the Orion nebula through the filter better on a dark night (no moon)?

Thanks!
Rob

Edited January 25, 2021 by RobH2020

[wibblefish]

I don't have any experience of the type of filter but I would imagine you will get better views on a darker night as a general rule with any filter as you will have more light to work with. That said M42 is a fairly bright nebula from what I have observed so it is likely still fairly visible even in bright moonlight unlike some other DSO's.

I would suggest you try it on both nights with and without the filter to see what you think is the best option 

[Kon]

The moon will have some impact but the Orion nebula is bright enough t see. I was out in Saturday from a bortle 4 sky with an 8" Dob and i could see it. It had less features than without the moon. Light pollution will of course impact. Did you mange to see it at all?

 

[RobH2020]

1 hour ago, Kon said:

The moon will have some impact but the Orion nebula is bright enough t see. I was out in Saturday from a bortle 4 sky with an 8" Dob and i could see it. It had less features than without the moon. Light pollution will of course impact. Did you mange to see it at all?

 

Oh yeah I could easily see it, it always looks like a giant manta ray to me, so i could see its big wings spreading out a long way, and its mouth near the trapezium!

I would definitely expect fewer features to be visible with the moon washing it out when looking at the full spectrum of light, I just wasn't sure about with the UHC filter...

[John]

All nebulae will look better in a dark sky regardless of whether a filter is used or not.

Filters like the UHC and O-III  enhance the contrast of emission nebula by permitting the wavelengths of light that they emit while excluding most other wavelengths. So they help to see the nebula a bit more under moonlit conditions but under a dark sky will have even more impact.

 

 

 

Edited January 25, 2021 by John

[John]

2 minutes ago, John said:

Posted in error.

 

Edited January 25, 2021 by John

[Zermelo]

To put some pictures onto John's words:

The UHC passes light in a couple of visible bands, to catch the main nebula emission lines:

while cutting out most of the rest to improve the contrast.

 

But the moon just reflects most of the incident sunlight in a continuous spectrum:

So the UHC will cut out a lot of the moonlight, but will still transmit the parts within its bandpass regions, so reducing the contrast.

 

I was also observing M42 with (and without) an Astronomik UHC in the last few days, and I was surprised how little of the structure was lost, compared with previous dark nights.