Ha imaging with the moon

[Shibby]

I've been having a go at the heart nebula recently with my DSLR and Baader Ha filter. So far I have 2 nights' worth of data but the faintest areas are still rather noisy. I think this will mostly be thermal noise as it's been quite warm recently and I'm taking 10min subs with an uncooled DSLR!

My question is; if I go and gather a load more Ha data with a nearly-full moon, will this really be worthwhile? People always seem to claim you can do Ha imaging no problem with the moon out, but is this really true?? Some moonlight must make it through, so will the faint bits still stand out well from the background?

Maybe I've no hope in achieving a smooth narrowband image with DSLR, but I'm planning to gather as much data as possible to see just how far I can go.

Thanks

[Uranium235]

I guess it depends on where the moon is in relation to your target. If its right next to it, then I wouldnt attempt it myself. But if the moon is the other side of the sky or low down (and your target high up), then no problems - go for it!

[JacobvonChorus]

If the moon isn't right beside the target you are fine. I've imaged with 10min subs with the full moon not far away, and gotten a perfectly fine result. Yes some moonlight leaks through but it is insignificant and easy to deal with.

Jacob

[Earl]

I think the Moon at 10pm tonight M31 is 85 degrees away from the moon would that be OK for Ha?

[Shibby]

Well it looks like it's a good 50degrees away tonight, so I'll give it a pop! Well, I probably won't because it's bound to end up cloudy!

Earl, I'm not entirely sure how to calculate it but I think it's a bit closer than that isn't it?

[Shibby]

[Can we not edit posts at all any more?]

Just wanted to say, thanks for the comments!

[Earl]

Well it looks like it's a good 50degrees away tonight, so I'll give it a pop! Well, I probably won't because it's bound to end up cloudy!

Earl, I'm not entirely sure how to calculate it but I think it's a bit closer than that isn't it?

Id really like to know how

[Shibby]

I just used this calculator: http://celestialwonders.com/tools/starAngleCalc.html

For Heart -> Moon at midnight tonight I got 96deg, so I was way out! (or I used the calculator wrong...)

[Earl]

71d 12m 20.0s for my targets

[ollypenrice]

My feeling is that near full moon does affect even Ha images. I find they have significantly more noise. However, if you are going to combine the moon-time data with dark time data I think it will be worth having. You just have to suck it and see, I reckon. One thing I've found is that the low contrast in moonlight can make guiding more tricky. Has anyone else had this?

Olly

[pilkinn]

I'm attempting an imaging run in Ha at the moment of the Veil nebula and the moon isn't too far away. You're right Olly in that there is significantly less contrast in the guiding images but so far so good. I'll have to see how the stacking goes as I'll be combining tonight's subs with other subs from other nights where there was no moon at all.

[JacobvonChorus]

I have no guiding issues when imaging under the fulk moon.

Jacob

[JacobvonChorus]

I have no guiding issues when imaging under the fulk moon.

Jacob

[Shibby]

Well, there was too much cloud around last night to even attempt it. Looks more promising tonight, though, so I'll see how it goes with an even brighter moon!

I'm attempting an imaging run in Ha at the moment of the Veil nebula and the moon isn't too far away. You're right Olly in that there is significantly less contrast in the guiding images but so far so good. I'll have to see how the stacking goes as I'll be combining tonight's subs with other subs from other nights where there was no moon at all.

How did you images come out, Neil?

[martin_h]

No guiding issues here last night on the veil with the moon close by, the contrast was way down but not a problem. I'm on OIII subs and the moon does effect them slightly, the black point is a tad higher than usual and the contrast looks a bit flat, I havn't stacked them yet so cant realy tell.

[Shibby]

Well, they say a pictures tells a thousand words. I think these images clearly show the moon makes quite a big difference. Whether the subs are worthwhile or not I have yet to find out - it looks as though with a quick process there is some reasonable signal to pull out but I'll see how it comes out when all stacked together.

On the left is a 10min Ha ISO-800 sub with no moon, with the levels stretched.

On the right is the same exposure but with a 97% full moon; the levels are stretched the exact same amount.

[ollypenrice]

Ouch, this is pretty much what I found. (I say found because I no longer do it. Moon time is bed time for me.) However, what happens if you cut back more aggressively on the moon-affected image? Can you rescue the contrast?

Olly

[Shibby]

Yeah, from the playing I've done so far it appears the background can be processed out to improve the contrast. I've also just discovered that it's a very good idea to use Per Channel Background Calibration when stacking these 2 sets of data together.

Thankfully, the noise does seem to have reduced, even in the fainter areas. Some extra work is required on the contrast, but even then the noise is significantly reduced (total integration time is doubled with last night's set).

Olly, I didn't have any guiding troubles (at least, once the wind had died down). However, I always guide on quite bright stars anyway because I use an unmodded webcam. As I say, the wind was a nightmare for some time until eventually the weather settled and resulted in this very pleasing graph