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Bortle 8 to 4 in Full Moon

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#1 FLord

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Posted 31 October 2020 - 01:42 PM

Hi,

 

I live in a Bortle 8 location, where the NELM is about 3.8 at the zenith. (SQM ~18.66)

 

Very unfortunately, my trip to a Bortle 4 location (SQM ~ 21.2) has coincided with the Full Moon. Today (ignoring the partly cloudy conditions with moderate transparency) the NELM is about ~4 at the zenith.

 

Before I called it a day I tried M57 in my portable 100mm reflector. I couldn't make out the Ring Nebula, at all.

 

Cygnus & Lyra were away from the moon and slightly better than home (we're talking naked-eye Sheliak, Sulafat & Albireo undecided.gif) but Cassiopeia, Pegasus and Andromeda were utterly washed out. This is is especially annoying as they are behind a house at home.

 

Is it worth observing when the moon is about 10° up? What can I observe, if anything, better than i do at home? How will globs, open clusters etc be affected?

 

And a final question: what am I missing out on? (some of the milky way maybe (?) .Frustratingly, I've  been to a Bortle 3 location before on holiday, before I took up astronomy, and didn't look up!

 

Thanks again.


Edited by FLord, 01 November 2020 - 05:55 AM.


#2 RocketScientist

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Posted 31 October 2020 - 04:09 PM

When the Moon is up, focus on small objects with high surface brightness. Use as much magnification as possible. Ignore anything within 20 degrees of the Moon.

This suggests focusing on double stars, planetary nebulas, the brightest globulars, etc.

Don't bother with bright nebulas. Galaxies? Forget it.
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#3 esd726

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Posted 31 October 2020 - 06:09 PM

Hate the Full Moon. 


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#4 BrooksObs

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Posted 31 October 2020 - 07:51 PM

Hi,

 

I live in a Bortle 8 location, where the NELM is about 3.8 at the zenith. (SQM ~18.66)

 

Very unfortunately, my trip to a Bortle 4 location (SQM ~ 21.2) has coincided with the Full Moon. Today (ignoring the partly cloudy conditions with moderate transparency) the NELM is about ~4 at the zenith.

 

Before I called it a day I tried M57 in my portable 100mm reflector. Icouldn't make out the Ring Nebula, at all. Cygnus & Lyra were away from the moon and slightly better than home, but Cassiopeia, Pegasus and Andromeda were utterly washed out. This is is especially annoying as they are behind a house at home.

 

Is it worth observing when the moon is about 10° up? What can I observe, if anything, better than i do at home? How will globs, open clusters etc be affected?

 

And a final question: what am I missing out on? (some of the milky way maybe (?) .Frustratingly, I've  been to a Bortle 3 location before on holiday, before I took up astronomy, and didn't look up!

 

Thanks again.

 

When under ~3 degrees elevation it is possible to still do some limited deep sky object observing even at full moon, providing that the object of interest is 60 degrees or more removed from the moon. Nevertheless, it won't be comparable to what you might see in that same Bortle 4 sky without a moon. And if the gibbous, or full moon is any high up, then it is time to turn to the planets, double stars, or similar features that will suffer much less from moonlight.

 

BrookObs


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#5 erick86

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Posted 01 November 2020 - 11:19 PM

I’m planning an early session tomorrow morning, and the moon will still be high in the sky. It’s a good time of month to hunt down the brighter Messier open clusters, since the stars in them are usually fairly bright and distinct and not as easily washed out. Anything that is seen as a diffused object under a really dark sky (galaxy or unresolved globular cluster, or comet) is quickly obliterated by a bright moon.

In general, the light from a full moon at a dark site has similar effects to the light pollution downtown with no moon. So not really much benefit to leaving the city during a bright moon, I find. You’ll find all the same brighter deep sky objects from the city.
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#6 alphatripleplus

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Posted 04 November 2020 - 09:58 PM

I usually quit trying to  observe any extended DSOs (galaxies or nebulae) once the moon has cleared the horizon.


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#7 birger

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Posted 05 November 2020 - 02:15 AM

The full moon is ridiculously bright. The moon is peculiar, as it gets a "boost" of brightness once it's in full phase. That means, a full moon is NOT twice as bright as a half moon, but rather 10-12 times brighter (a full moon is approx. -12.72, while a half moon is about -10 mag.). In fact, a full moon is about twice as bright as a 95% illuminated gibbous, so the few days around full moon gives a dramatic change in light received from the moon.

 

A full moon ruins a night unless you need its light to navigate. A full moon itself isn't interesting to look at either. You can't really see much features on the lunar surface, except for the maria.

 

I remember seeing about +5 mag. stars with a full moon up, but I guess transparancy were more or less perfect. Milky Way invisible of course, even through Cygnus. Perhaps one could have seen it through Sagittarius, but it wasn't visible from that location.


Edited by birger, 05 November 2020 - 02:17 AM.

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#8 FLord

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Posted 05 November 2020 - 06:51 AM

The full moon is ridiculously bright. The moon is peculiar, as it gets a "boost" of brightness once it's in full phase. That means, a full moon is NOT twice as bright as a half moon, but rather 10-12 times brighter (a full moon is approx. -12.72, while a half moon is about -10 mag.). In fact, a full moon is about twice as bright as a 95% illuminated gibbous, so the few days around full moon gives a dramatic change in light received from the moon.

 

A full moon ruins a night unless you need its light to navigate. A full moon itself isn't interesting to look at either. You can't really see much features on the lunar surface, except for the maria.

 

I remember seeing about +5 mag. stars with a full moon up, but I guess transparancy were more or less perfect. Milky Way invisible of course, even through Cygnus. Perhaps one could have seen it through Sagittarius, but it wasn't visible from that location.

Indeed. I've come back now, and can report on my observations.

 

The night on which the full moon fell was very poor, as you say: NELM in the high 3's. However, two days after, I was able to observe M31, M103, Double Cluster, Alpha Persei Cluster, M15 & M71 (very faint), the tiniest hint of the Dumbbell Nebula, and a few other DSOs,  all in my 100mm. Some views were pretty good, some were mediocre and some were probably not worthwhile. But it's the most objects I've ever observed in a day, so all in all it was a nice experience. 

As you say there was no hint of  Milky Way visible at all, which was quite annoying. I wonder how much more I could've seen in my 5" spherical f/7 (Explorer 130/SpaceProbe 130) but it isn't very portable.



#9 aeajr

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Posted 07 November 2020 - 11:24 AM

Indeed. I've come back now, and can report on my observations.

 

The night on which the full moon fell was very poor, as you say: NELM in the high 3's. However, two days after, I was able to observe M31, M103, Double Cluster, Alpha Persei Cluster, M15 & M71 (very faint), the tiniest hint of the Dumbbell Nebula, and a few other DSOs,  all in my 100mm. Some views were pretty good, some were mediocre and some were probably not worthwhile. But it's the most objects I've ever observed in a day, so all in all it was a nice experience. 

As you say there was no hint of  Milky Way visible at all, which was quite annoying. I wonder how much more I could've seen in my 5" spherical f/7 (Explorer 130/SpaceProbe 130) but it isn't very portable.

My sky NELM is about 3.7 when there is no Moon.

 

Understanding ground and sky light pollution is the key to dealing with light pollution.

 

Light Pollution
https://telescopicwa...ight-pollution/



#10 FLord

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Posted 07 November 2020 - 01:13 PM

My sky NELM is about 3.7 when there is no Moon.

 

Understanding ground and sky light pollution is the key to dealing with light pollution.

 

Light Pollution
https://telescopicwa...ight-pollution/

Interesting. How's your telescope limiting magnitude (aperture-dependent as it is)?



#11 aeajr

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Posted 07 November 2020 - 02:46 PM

Never tried to gauge a limiting mag of the scope.   


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