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What causes "glow" around planets?

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#1 REC


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Posted 31 August 2019 - 10:56 AM

The last few nights,the seeing was pretty good, 4/5 with moderate 50% humidity. When looking at Jupiter, I get a glow around the planet with just medium power. Same but not as bad on Saturn. I was using a Baader moon & skyglow filter in the diagonal. If I dropped the power down, it goes away and in Saturn's case, had it real sharp but small in a nice field of stars. Jupiter was better, but not the best.


I was using my C102 f/1000 f/9.8 scope and a Baader 8-24 zoom. When I switched out to my very good 19mm Pan 50x the glow was gone and a very pleasant site overall.


So, what causes this glow, water in the air, too much power, quality of eyepiece ect?



#2 WarmWeatherGuy



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Posted 31 August 2019 - 11:15 AM

I would also like a good answer to this question.


One answer for me was my diagonal was dirty and cleaning it helped a lot but it didn't get rid of it completely. It is most noticeable on bright objects like Jupiter and Venus. I think the problem is some sort of haze in the optics that you don't notice unless you're looking at a bright object.

#3 db2005



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Posted 31 August 2019 - 11:32 AM

Since you report that the glow was gone when using the 19mm Pan it stands to reason that the glow was caused by internal reflections or light scatter inside the Baader 8-24 zoom. Part of what you pay for with premium quality eyepieces is better control of stray light / light scatter / internal reflections, which is accomplished by internal blackening, better lens polish and better lens coatings, etc.


The most common causes for "glow" or light scatter around planets I have experienced are (in no particular order): atmospheric conditions (haze/light pollution, etc); fogging of optics (main objective and/or eyepieces); poor quality filters (one I tried once caused an almost unbelievable amount of glow around the Moon); using a poor quality erecting prism diagonal (erecting prisms can cause a lot of glow/glare/spiking artifacts that a normal star diagonal doesn't); internal reflections/light scatter in eyepieces. Tube currents during acclimatization can also cause poor performance but I haven't noticed any glow caused by that, but flaring around bright objects is very common in my 4" refractors during their acclimatization process, and usually lasts for 45 minutes to an hour under my observing conditions.


Diagnosing optical problems usually involves swapping components in the optical train one by one, ideally also trying to remove the diagonal and observing straight through to eliminate any artifacts introduced by the diagonal.


You don't mention the color of the glow, but one point worth noting is that your C102 is an achromatic refractor, so some modest but visible amount of blue/violet haze around bright objects like planets (and Jupiter in particular) is to be expected due to the blue/violet colors not being focused. This is not a defect of the telescope, but rather a property of the optical design of achromatic refractors.

Edited by db2005, 31 August 2019 - 11:32 AM.

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#4 Tyson M

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Posted 31 August 2019 - 11:48 AM

Great post above ^, seems to be in line with what I experienced. 

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#5 39.1N84.5W


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Posted 31 August 2019 - 12:10 PM


#6 azure1961p


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Posted 31 August 2019 - 12:19 PM

It's a few things


1.The atmosphere scatters light a bit. Less apparent in Saturn due to dimness.


2.Dirty optics


3. Optics with rough polishing.


4. The eye itself.


Live long and prosper.



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#7 fcathell



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Posted 31 August 2019 - 09:59 PM

A dirty eyepiece lens (eye lens usually) will do it.  If I see a "haze" around a planet on a clear night with no clouds, atmospheric haze, etc, I will usually try another eyepiece.  If it goes away I get out the alcohol, distilled water, and a Q-tip and go to work on the eyepiece.



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#8 jeffmac


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Posted 10 September 2019 - 08:42 PM

I live in NC too and lately, experienced a yellow glow around Jupiter and Saturn. I found out that an eyepiece that was in the cool of the air conditioned house was the cause. Also, getting your eye too close to the eyepiece can cause fogging that displays a glow around planets.

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#9 aa6ww



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Posted 11 September 2019 - 10:19 PM

Warm up your eyepiece and more then likely it will go away.


This happens mostly when the eyepeice is cooler. Take your eyepiece out of your diagonal and hold onto it with your hands and let it warm up, or put it under your arm for a minute and then put it back in your diagonal. 

I see this every year as the seasons begin to change. This happens to colder eyepiece. You can watch the glow just disappear if you wrap a dew heater around it and watch the glow just fade away.


Cover your eyepieces when your not using them and keep them out of the direct path of dew and cooler air.  Put a glove over the eypiece or just drap a small towel over it when your eyes arent over it. You dont have to see dew on the eyepiece, thats not what this is.


Try it, watch what happens.


This seems to happen consistently on Jupiter and Saturn as the seasons change.



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