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Observing in moonlight

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potterrb's picture
Observing in moonlight

Hi All,

I am a visual observer by choice. For years I struggled with a portable photometry setup, wheeling out a reasonably high end Goto setup (200mm reflector on Tak EM200, SBIG with UBVRI filters), but I found that many nights I would work until 2-3am just trying to get everything working in anticipation of a couple hours of photometric imaging before dawn. Completely frustrated, I decided to sell that setup and go completely visual until I can afford to setup a permanent observatory. I learned a good deal about photometric imaging and image reduction during that period which I am sure I can Leverage when I get back to it.

For now, I am enjoying visual variable star observing. Not only that, but I have gone eau naturale, replacing my old setup with a 10-inch dob and binoculars. I have assembled both a binocular and a telescopic variable star observing program and am becoming fairly adept at star hopping and visual observing, and am now working at increasing my tempo/productivity during observing sessions.

My question goes out to those experienced visual observers out there who also choose to star hop. What do you do during nights around a full moon, like tonight? Do you just pack it in, or do you have a strategy to remain productive in spite of the moon? I am already light pollution challenged here in suburban Detroit, but during moonlit nights find it difficult to star hop with much success. Your experiences and advice would be most appreciated.

Thanks -- Brian

SNE's picture
Hi Brian, Years ago I

Hi Brian,

Years ago I watched a lot of cataclysmics with a buddy.  Most observations were "fainter thans" and with our 12-inch telescope we often were seeing 14th magnitude stars in our suburban sky.  Unless the sky was really hazy with humidity (typical of Upper-Midwest summers) we could still do these cv's provided we turned the dome to block us from direct moonlight and avoided looking out onto the landscape.  Star hoping was quite the challenge on those nights.  Our "fainter thans" were not nearly as faint, but they provided the observations to show that outburst did not occur.  We avoided red stars on these nights as well since the moonlit sky seemed to enhance them and we did not trust our estimates.  This way we got something out of the evening and at the last we would indulge in some thrill seeking by turning the telescope to the moon and ruining our night vision in the exploration of what little of the lunar terminator was available.


Neil Simmons (SNE)

PYG's picture
Re: Observing in Moonlight

 Hi Brian,

Like you I too live in a high light pollution city - Birmingham, England - so I immediately sympathise with your conditions.


As a visual observer who uses a Dobsonian, I have always observed in any Moonlit conditions.  I find that after VS observing for nearly 40 years, I can point the scope to the part of sky I want to be and be pretty close to the field on first attempt. I then use a large'ish finderscope to drop me onto a field star and away I go.  You will find this becomes easier to do the more time you spend doing it. You might also find that an extra light shield around the 'back edge' of the scope projecting about 18 inches above the top of the tube is a good idea too. This prevents Moonlight (and in my case bedroom lights too) from illuminating the eyepiece field, and you can get quite close to the Moon if you use one of these.  I use heavy duty black card which is fixed with velcro.  I take it off when 'old white face' isn't in the sky or if it's windy!  There are of course some occasions when the Moonlight is just too overpowering (high in the sky with high clouds scattering light). On these occasions I might spend time with my back to the Moon and concentrating on other area's of the sky, but I will always go out and observe.  Who knows what CV activity you might detect!


It's always great to hear of someone who has taken up visual VS observing, and I wish you lots of luck with it.  


Gary [PYG]

potterrb's picture
Observing in moonlight

Hi Gary,

Thanks for the feedback! Your observing career is legendary, and  I would have imagined based on the sheer number of observations you have made that you were not deterred by moonlight, light pollution, or a few measly clouds.  That in itself is encouragement enough for me to just get out there and get it done!

I do have a set of circumpolar targets, had considered them to be prime for moonlit nights since they would put my back to the ecliptic. I'll try the light shield as well, and see if that helps.

Thanks again!

pox's picture
I side with my compatriot

I side with my compatriot Gary - although I don't observe when the Moon is absolutely full (respect!!) Generally I find that once you get used to star patterns down to about 7th-8th mag a low power wide-angle eyepiece does it. You soon get used to these patterns - examples might be the wide double just north of the coathanger that sits on top of WW Vul, the little equilateral triangle whose 'bottom' edge points east to the guide stars to V Sge, the asterism around gamma Cam that is useful for finding several faint variables nearby. The bright asterism between beta and gamma Cep is also very useful for finding some of my fave YSOs in the area (BO, SV, BH, BI Cep). And of course some variables are simply near bright stars, such as RT Dra.
Another way of 'screwing up your instrument' pace Herschel (I assume the phrase meant something entirely different in his day) is to have as many matt-black surfaces as possible, especially both inside and outside of the tube, areas around the eyepiece, and so on.

Best of luck with your dual organic variable star detectors!

HNL's picture
observing in the moonlight

Hi:  Well, there is always doing fix up around the scope. I have taken to naked-eye observing sometimes. Our club has a full moon night and we have a workshop day. Reading a book. Thinking about the moon.  Checking out the Nasa website to see if they are really sending robotic scopes to the moon for people to observe there.  Doing a lot of retrospective  thinking.

   What ever works, That is pretty much it.   

SXN's picture
Observing in Moolight

It is a harder to star hop in moonlit and light polluted circumstances. I have a few things for you to consider that may get you a couple more nights per month.

Use a larger finder scope. I have an 80 mm short tube refractor that makes it a lot easier to find my way around with. It also doubles as a small aperture scope for bright targets, like Nova Del 2013 or Miras at max, brighter than I want to observe with my 12".

Customize your target list to only go after the variables that are easy to find. Some variables are close by bright stars, Messier objects or star clusters you can easily hop from. Skip trying to wade through Leo or Virgo where there's next to nothing to help you find your way. Come back to them when the Moon goes down. 

Put something between you and the Moon, like a building or a hedge, or Gary's trick of using a light shield. A bright sky not only makes it hard to star hop, it keeps you from getting fully dark adapted, which doesn't help anything. Try getting out of the light. 

There are plenty of cloudy, or in our case bitterly cold nights, for staying inside and reading or spending time with the family. Don't let the moon chase you away if you don't have to.

Let's sway under the moonlight, 

This serious moonlight

David Bowie, Let's Dance

lmk's picture

Hello Brian,

Like you, near the beginning of my observing career, I toyed with CCD ("cookbook" and portable setup) and quickly became frustrated just fiddling with it to get it to work! I gave up on the likelihood I would ever get it to give me measurements as good as my own eyes can. Of course, nowadays, the equipment and software has become much more "turnkey" and likely to be less of a pain to use (but also quite pricey compared to a basic large Dob).

So, I applaud your decision to stay visual. We so need more observers like you and me out there contributing!

Regarding the problems of bright moonlight - well you hit a tough one there. I'm sure it negatively affects every visual observer to some degree. I typically do only a third of the number of stars under bright moon than under dark skies. As you know, the bright background really changes the appearance of star patterns for star hopping. "Squares" become triangles when the fainter star disappears into the moonlight, etc. Slows me down by a factor of 3, I have to take a lot of time to find the right field and verify again I am still looking at the proper place. Add in clouds and haze, and pretty much you can forget star hopping for the more difficult ones!

So, I end up concentrating on the brighter variables and ones located near bright stars or patterns during the bright moon. Examples are - HL Cma next to Sirius, HV Vir near a bright star pattern, T Crb bright and easy to find, etc. And leave the fainter variables for the dark nights. So, it kind of works out pretty well this way.

Mike LMK

potterrb's picture
Observing in moonlight

Thanks all for your feedback...I'm sufficiently motivated to get out there and observe on moonlit nights.  Between circumpolar targets, brighter & well placed targets, and light shielding techniques I will work to get the most out of these far less than ideal nights.

And Mike S you're absolutely right about our bitterly cold nights.  My brother is a biker and suggested heated motorcycle gloves.  Between that and a trip to Cabela's to check out their cold weather hunting gear, even the cold may not be able to stop me!

Clear Skies,

WWJ's picture
  GO TO !   OK, I




OK, I appreciate that most observers in this discussion haven’t this facility on their scopes – in parenthesis; there's also this strange notion that it's not quite playing the game to use GOTO's.


I operate GOTO throughout my sessions. There's enough star hopping even with it: sometimes the location's not precise, or one's in doubt about the orientation of the field. Even in the case of a well known position, there's time for a few gulps of a hot drink or a shuffling about of charts whilst droning along to the next target.


Fully endorse large finders. I added an 80mm finder to my Celestron 11' SCT. A crucial advantage over the supplied 9x50; which I only employ now for aligning. Everyone should have one...needn't be pricey.


Seldom driven to exploring the Moon with these provisions. A clear moonlight sky, subtracts not more than one magnitude... if that.

PYG's picture

Without wanting to start up a 'for and against GOTO mounts' thread (again), I have to say that having used an exceptionally accurate GOTO for a few years, I got absolutely bored to death with it. Sitting there twiddling my thumbs whilst the scope went from start to star.  Nah. Too slow!  Adding stars to my list without knowing whereabouts in the sky they were (I didn't need to know)!!  What was I becoming?  I saw the light and went back to a Dob!

GOTO's?  Been there, done that and threw the T-shirt away :-)

Gary [PYG]

WWJ's picture
To Go To...


Well... there you have it folks.


“To go to, or not to go to”. Let the jury withdraw! Bear in mind, though, that Gary's a top rank visual observer of vast experience. We're talking to lesser mortals in this discussion – like myself, for instance.


I must say, though, I've never experienced “boredom” out there in the night; but, perhaps I'm rather easy to entertain?


I take it we're in broad agreement on the matter of big finders. As a codicil; the field here needs to be the same way up and the same way round as in the eyepiece of the scope!

pox's picture
POX is with PYG again (at

POX is with PYG again (at least we support different football teams).
GoTo's are NoNo's. Just learn your way around the sky - it's not rocket science ;-) and as Gary says, it's much much quicker. Sometimes I sight along the tube, just for fun. I do agree that you need a decent finder though, and one that presents the field in the same orientation as the main scope.

TYS's picture
Moon Light Observing

Brian, I will observe variables even under a full moon. I simply go for those variables that are as far away from the moon as possible. Rich (TYS)

drob's picture
Observing in Moonlight

Hi Brian,

In Vermont if it is cloud free there is either a full moon or it is -20 F outside.  During  full moon I shy away from making observations,  shortly before or shortly after I go after the brighter stars, or stars located far away from the moon.  I am bless with dark skies, theoretically the limiting magnitude of my 8" Dob is 14, in reality and with my bad eyes it is around 13.5.  With the full moon up one can easily knock off a couple of magnitudes from the limiting Magnitude, so one can tailor ones observing list for the full moon.


Cheers and clear skies

Bob in VT

Aldebaran's picture
Observing in moonlight

I'm a visual observer, and I'm doing 99% of my observations with either 4'' or 3'' refractors. I don't use any kind of GOTO, I'm only doing star-hopping.

I'm living in Finland, where we have really cold winters! During summers, the night are light, and only the brightest stars can barely be observed in southern Finland. And added to this, in our climate it is often very cloudy, especially during winter months.

During moonlit nights, I'm also observing! I can do observing efficiently if NELM is around 4.0 and SQM reading about 18.0. The observing conditions can be like this during moonlight night or in a night during mid May (when the white nights are beginning) or late July, when the nights are getting dark again.

When observing during moonlit nights, I'm only avoiding the area very close to the moon. Otherwise you just have to be more careful with recognizing the star patterns in the sky!


Juha Ojanperä (OJMA)

Turku, Finland

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