Does the moon effect your guiding & PHD2? - Forums

Topic starter

Jan 25, 2021

It might just be a coincidence or due to another factor (seeing?), but I'm noticing that my guiding gets better as the moon gets low in the horizon. If I image somewhat near the moon my guiding isn't as good as if imaging in the opposite portion of the sky.

Does anyone make any adjustments to PHD2 to account for moonlight?

I'm interested in the what/if any settings you change i.e. auto star detection, Minimum star HFD, exposure etc.

I'm using a asi120mmc and recently added a ir cut filter and my stars are much sharper and seems to have overall improved my guiding along with using the beta version of PHD2 with multi-star guiding.

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J21_Jas

Feb 28, 2021

I'm a complete newbie to this, but is there a way to compensate for the moon's presence without dimming the rest of the image? I get that the moon, especially when full, can be a source of light that prevents from getting an ideal picture of the rest of the sky, but is it possible, before you take the picture, to reduce only the moon's light, and not the rest's?

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andrea tasselli

Frequent contributor

Feb 28, 2021

Using a narrowband filter would do that. However they are going to be useful only for emission lines objects (e.g. diffuse nebulae such as M42 or M57). Not much good if your into imaging galaxies or reflection nebulae.

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John Hayes

Frequent contributor

Exemplary contributor

Feb 28, 2021

Hahahaha! Yeah...when the moon is full, the seeing always seems excellent and guiding is perfect. The seeing always seems to go all to heck when the moon is new and my seeing numbers look terrible.

Seriously, moonlight shouldn't have much--if any effect on guiding accuracy. Even if the contrast of the guide star goes down a little, that shouldn't significantly affect the accuracy of any guiding algorithm.

John

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Bob Lockwood

Feb 28, 2021

Seriously, moonlight shouldn't have much--if any effect on guiding accuracy

I’m with John on this. The moon or moon light should have no effect on guiding regardless of the program your using. Not sure why you would try to image under moon light unless you were doing NB anyway, and you typical don’t guide through filters.

andrea tasselli

Frequent contributor

Feb 28, 2021

Bob Lockwood:
Seriously, moonlight shouldn't have much--if any effect on guiding accuracy

I’m with John on this. The moon or moon light should have no effect on guiding regardless of the program your using. Not sure why you would try to image under moon light unless you were doing NB anyway, and you typical don’t guide through filters.

Indeed it does not. As for imaging with Full Moon I beg to disagree. There is plenty to do even when the Moon is full. I spent 7 hours just yesterday night and they weren't star clusters. And no NB filter, as that is cheating ;)

David Redwine

Mar 4, 2021

If the moonlight illuminates the objective of your guide scope the answer is yes! If not then the previous posters are correct.

Jared Holloway

Mar 4, 2021

I have never had any issues with my guiding with a Full Moon or a New Moon or anywhere in between - that being said, I always have great SNR looking SE - S and terrible SNR looking NE - N

(Bortle 8 skies)

AwesomeAstro

Mar 4, 2021

Short answer; no, there should be no relationship.

Long, creative answer; there's a ridiculously roundabout way in which you might have problems from this. When this happens, check your actual guide star. Is it round, or at least a single blob? If so, this shouldn't matter.

However, if the guide star (due to seeing, optical imperfections, etc.) is blobby with multiply lobes, then light pollution from the moon could indirectly hurt you (it doesn't cause the blobbiness). Whenever I have a lumpy guide star (here, due to bad seeing), the guiding jumps around terribly because Phd2 is trying to locate the centroid, and sometimes it places it on one half of the blobby star, and sometimes on the other. Even if it's not moving around, the program will think it is. Bright light pollution could decrease the guider SNR enough to exacerbate this problem, although not cause it.

If your star is round and/or is a single blob, this isn't relevant.

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ChrisPeace

Mar 6, 2021 · Edited: Mar 6, 2021

I’d have thought that the SNR of the stars would have to be adversely impacted. If guiding with a OSC camera, which he is, would that not be affected by a full or very bright moon near the target?

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