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High transparency makes such a big difference

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#1 CrazyPanda

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Posted 04 August 2019 - 11:42 PM

Tonight I had one of the top 3 most transparent nights I've had from my backyard observing location.

 

It seemed like all my eyepieces had O-III filters on them. The football shape of M27 with converging shell wisps was very obvious. Those wisps *almost* touched even without the O-III filter. Adding an O-III brought the outer extents of the football into clear view at 214x.

 

Swinging over to the Cat's Eye Nebula (NGC 6543), I don't know if it was my imagination, but it looked like you could see the outer shell glowing very faintly around it at 571x

 

The Fireworks galaxy NGC 6946 showed very faint but visible spiral structure in averted vision at 137x.

 

The southern edge of the North America nebula was strikingly obvious in an OIII filter and 28mm RKE. The Gulf of Mexico region was sharply defined. I had never realized how easily this object could be seen. I actually wish I had a smaller rich field instrument for it.

 

The Veil was was incredible. I spent about an hour with it. Never saw so many knots and wisps and tendrils before. I desperately need a modern 2" O-III!

 

M17, M8, and M20 with O-III were incredible. I've never seen such strong definition in the Trifid before. The Swan was just a small part of the mass of nebulosity I could see in M17. M8 was loaded with well defined structure.

 

The central star of M57 was far more intermittently visible than it has been, even with mediocre seeing.

 

The Draco Group and several other Draco galaxies were strongly pronounced.

 

M81's brightest star cloud was obvious, though I could not quite see a well defined spiral structure due to the low altitude it was at at the time of observation.

 

M31's dual dust lanes were very high contrast tonight, in spite of its low altitude in a light polluted area of the sky. The bright star cloud on the western side of the galaxy was also obvious. Would have loved to have seen this at the zenith. Guess I'll have to wait until late September.

 

The Milky Way in general was almost distractingly beautiful. I had to force myself to look through the telescope tonight :p


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#2 Feidb

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Posted 05 August 2019 - 08:33 AM

Transparency is the key for deep sky. It rates well above seeing as far as I'm concerned. Unless you're after high magnification planetary nebulae or double stars or something, to me, seeing takes a back seat to transparency every time. Of course, it's always better to have both, but usually, I've found that if the transparency is good, the seeing isn't too far behind. Not always but...

 

On most nights, I find the transparency to be uneven. That seems to be the thing the past few years, no matter where I'm at. It'll be clear as a bell one direction while in the other, stars will have nebulae around them that aren't supposed to be there. Not good. Then I'll go back to the clear spot and find it "muddy," while somewhere else will have a clear patch.


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#3 Jeff Morgan

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Posted 05 August 2019 - 09:02 AM

On most nights, I find the transparency to be uneven. That seems to be the thing the past few years, no matter where I'm at. It'll be clear as a bell one direction while in the other, stars will have nebulae around them that aren't supposed to be there. Not good. Then I'll go back to the clear spot and find it "muddy," while somewhere else will have a clear patch.

 

Not surprising to me. Six years ago I was working on an article for CloudyNights on eyepiece coatings (March Madness for Eyepieces). The basic idea was to use Roland Christen's "Sidewalk Test" to photograph blue sky reflections coming back from an eyepiece and then compare histograms between eyepieces.

 

On my trial runs I would start getting inconsistent results. Looking up I could just barely tell the sky was not quite right, then my nose told me the story: smoke. The Forest Service was conducting a controlled burn that day and as the wind picked up mid day the edges of the plume drifted over my location.

 

Days after the burn ended I did another run and noticed more inconsistencies. Looking up, thin streaks of cirrus cloud were observed. How thin? Gossamer. At night I doubt I would have been able to see them.

 

It does not take much high cirrus (or smoke particles) to make a difference in transparency. And given typical wind speed at those altitudes (ballpark 60 knots during the summer), cirrus can move from beyond the horizon to a ground vantage point quickly.

 

And perhaps more often than we realize.


Edited by Jeff Morgan, 05 August 2019 - 09:03 AM.

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#4 paulsky

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Posted 05 August 2019 - 09:32 AM

Which telescope CrazyPanda you use?ç

Thanks

Paul



#5 CrazyPanda

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Posted 05 August 2019 - 11:59 AM

Which telescope CrazyPanda you use?ç

Thanks

Paul

15" F/4.5, sorry meant to mention that.


Edited by CrazyPanda, 05 August 2019 - 06:35 PM.

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#6 jtsenghas

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Posted 05 August 2019 - 08:34 PM

Yes, for DSOs transparency is almost everything! I now live close enough to Lake Erie that transparency is so often.... "meh", they when I get a week like the last one I get very little sleep. I must rise for work at 5:30 am, and even worked Saturday.

 

It appears that much of the country has had a good week of transparency, except for the regions plagued with smoke.  I've had a good run this week by local standards.

 

I can't wait for real astronomy trips to high altitude clear dry skies.

 

Someday.... 


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#7 stargazer193857

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Posted 06 August 2019 - 12:37 AM

I've seen this too. Transparency matters more than aperture. My best view ever of the Pleiades was naked eye. Blew away anything I've seen in a scope since. My best view of the double cluster was in a 130mm scope. The star density was so intense. Then it darkened to wine before my eyes in the eyepiece, back to normal.

The best scope is the one you take with you and use often so you catch the good skies. That does not mean the smallest scope. It must be big enough to satisfy.

#8 paulsky

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Posted 06 August 2019 - 09:32 AM

Then, transparency, and dark skies it would matter much that the apertura ?

Regards,

Paul



#9 Keith Rivich

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Posted 07 August 2019 - 04:55 PM

Had one of these nights a few years ago. Along with a "10" for transparency we had an "11 (out of 10!)" seeing. 

On that night we started out about average. As the night progressed the temperatures dropped until around 2am then settled down at around 24 deg f. I had a 1/2" of ice on my eyepiece case!

 

That's when the magic happened.

 

We (myself and Larry Mitchell) put his 36" scope on the Egg Nebula. Take a look at the picture. At 1000x it looked just like that, albeit a little smaller. No fooling. It was astounding! We went on to look at quite a few other DSO's with equal results.

 

Daybreak sent us in and the next night we were back to average. Sigh.


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#10 CrazyPanda

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Posted 07 August 2019 - 07:25 PM

Then, transparency, and dark skies it would matter much that the apertura ?

Regards,

Paul

It really depends on the objects you want to look at, but generally yes, aperture is not a substitute for dark skies and transparency.

 

Small bright planetary nebulae are visible even in somewhat heavy light pollution, and big aperture can show you a lot of detail in those objects.

 

Faint galaxies benefit from dark skies, because their contrast is so low.

 

Faint nebulosity (especially large nebulae like M42 and the Veil) benefit strongly from dark skies. M42 doesn't get that much better in bigger apertures, but it does get a lot better in darker skies.

 

But globular clusters like M13? No substitute for aperture. You can "fake" dark skies by increasing magnification to dim the exit pupil, but the stars themselves will get brighter directly proportional to the square of the aperture. For M13, I'd take a 16" telescope in light polluted skies over an 8" aperture in dark skies. But the opposite would be true for an object like M31 or M42.

 

Transparency though is a killer. Definitely would prefer high transparency over aperture for almost all objects (except planets).


Edited by CrazyPanda, 07 August 2019 - 07:27 PM.

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#11 NorthernlatAK

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Posted 07 August 2019 - 07:49 PM

During exceptional transparency I can see rusty-pink in the wings of m42 and grey-pink around the outer edge of m57. Saw this only twice in my 8" dob. M31 revealed dust lanes and it's true size on one of those nights. More is revealed as air clears up. Unfortunately where I am, those nights are usually extremely cold as well. My warmest exceptional night was 15°F but the first great night it was -20°F.
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#12 aatt

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Posted 07 August 2019 - 08:30 PM

I have not had a good night yet this summer. Just spent two days at my sort-of-dark site. I found the group of NGC's in between Pegasus and Pisces fairly disappointing with only two obvious members.M33, which has been great from that site, was not easy to see both of the main arms much less details within them except for the bright nebula at the tip of the lower arm.M101 was a barely perceptible spiral. I did get two members of the Hercules Abell (#?) cluster to the right of M13 though.Stephan's Quintet was a trio.Can't win them all-especially in the Northeast. A few years back in New Hampshire I had three nights of very good transparency in a yellowish/green zone and galaxies were everywhere in Andromeda. Pegasus and Perseus. Simply stunning series of evenings.Bad thing is, note the timeline-a few years back. Being in the right place (dark) at the right time (transparent) does not come often enough for me.Should a cleaned my mirror maybe, but I doubt it would have helped much as the mirror is really not very dirty. The globs were of course spectacular.



#13 Redbetter

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Posted 08 August 2019 - 02:29 AM

 

We (myself and Larry Mitchell) put his 36" scope on the Egg Nebula. Take a look at the picture. At 1000x it looked just like that, albeit a little smaller. No fooling. It was astounding! We went on to look at quite a few other DSO's with equal results.

 

 

I wandered over to that one last week after doing a few galaxies in Cygnus, hadn't researched it all in advance but figured since it had a name it would be easy despite the PK designation...I should know better.  Seeing was mediocre and I was looking for a larger planetary, not a small proto-planetary with the characteristics of a reflection nebula.  I was using minimum magnification at first, didn't see it, put in the OIII, didn't see it, went to 154x and realized there was something there but not enhanced with the OIII.  I figured it would be better to save it for a night of better seeing and higher power, so I moved on.  When I got home I confirmed that the odd thing I was looking at was it.

 

Contrast this with extremely poor transparency a couple of nights ago...I had actual thin cloud covering the whole sky shortly after set up.  I estimated NELM as less than 6 at a site that typically gives me ~7.  Decided to target the SN associated with NGC 7236.  No luck on the SN, as it is probably near 17 mag at this point.  But despite the lack of transparency and clouds lit up to about 21.2 MPSAS, half a magnitude brighter than the sky is on a transparent night, I was able to see the three galaxies essentially overlapping.  I was also able to track down 6 others in the surrounding are between 15 and 16g magnitude, but man were they difficult.  I kept seeing the first one while looking for the SN as the galaxy was preceding to the NW.  I logged them, but didn't really describe any of the 9 because there was so much contrast lost that the descriptions would have been meaningless as a guide later.  Most were mere detections rather than characterizations. 

 

That's what I get for preparing for a session with a nice chart...  Preparation is the kiss of death to getting a clear night or good seeing.  This past and present years' fickle weather have made me so superstitious about this that I have taken to unloading my truck even when I plan to go up the next night.  If I leave the scope loaded the weather is nearly always opaque...but if I unload, make other plans, and don't prepare an observing list, then skies magically clear a few hours before nightfall.  The universe hates organization...


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#14 Araguaia

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Posted 08 August 2019 - 11:20 AM

I just had a session with excellent transparency.  I was gauging it by looking at M33 by naked eye.

 

I found that if I put my hand out to block the band of the Milky Way, it became much easier to see M33 with direct vision.  Without the hand it would keep popping in and out.

 

Now, here is my point: M33 was just below 50 degrees altitude, and directly over what has to be the light pollution from the nearest town, 20 km away.  It is not a lot of light, and the trees hide it, it but when it is hazy I can make it out glowing faintly in the sky above.  So I would say that the sky in that direction could not be called Bortle 1.  But on nights of great transparency, it is an easy 1 on the Bortle scale, as evidenced by M33.  I think high transparency nearly eliminates weak light pollution.


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#15 Arcticpaddler

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Posted 09 August 2019 - 08:11 PM

Transparency trumps everything.  Last night I was camping in the Bortle 2 zone an hour north of my house.  After the moon set M33 was only vaguely visible to the naked eye due to the thin layer of high-altitude smoke from Alaskan/Canadian wildfires that has plagued this area on and off all summer.  The Milky Way was also subdued.



#16 havasman

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Posted 09 August 2019 - 09:50 PM

It's fun to read about transparency these days anyway. We have the typical summer pattern solidly in place - big high pressure system parked overhead, heat, high humidity and a haze so brown and thick I have to look twice late in the day to see if the high cirrus that take away the last potential for any observing are still in place. (>100 degrees f and dew points @ 75 degrees f) Last week I set up about 1am thinking it had "cleared" only to find clouds in place, high and thin but debilitating. 

 

I do still remember those transparent skies and hope to see them again. C'mon winter!


Edited by havasman, 09 August 2019 - 09:51 PM.


#17 Jon Isaacs

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Posted 13 August 2019 - 09:39 AM

This is an interesting topic to me.  There is no doubt that the darkness of the skies is very important and there are dark skies in many parts of the country.  But I also think transparency is important and typical transparency probably varies greatly with location, just as seeing does.  Dick describes the heat and high humidity that result in a brown haze. 

 

And I remember standing at an overlook at the Capitol Reef National Park.  There was sign that said:  "The average summer visibility from this point is 150 miles."

 

A few thoughts and questions:

 

What is your gut feeling about the typical transparency in your area?

 

What do you thinking are good indications of high transparency?

 

My gut feeling is that the transparency where I observe is probably better than average, probably much better than average.  It is located in the desert mountains about 70 miles from the Pacific Ocean so the high altitude transparency is generally determined by winds from the Pacific, not a lot of pollution and smoke. The local humidity is typically quite low, day time very often under 20%.  

 

One indicator of transparency seems to be the blueness of the sky.  Visitors from the midwest often comment on just how blue the sky is out west. How often does your chart look like this?

 

clear sky chart 8-13-2019.jpg

 

(That's tonight)

 

Jon


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#18 Jeff Morgan

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Posted 13 August 2019 - 10:35 AM

A few thoughts and questions:

 

What is your gut feeling about the typical transparency in your area?

 

What do you thinking are good indications of high transparency?

 

1) My area, generally excellent. Humidity is often under 10% Typically over 100 miles of visibility. High pressure domes that linger too long can change that though. The air does not "cleanse" itself through convection so ground sources of contaminants (dust in my area) get trapped in the lower atmosphere.

 

2) I use horizontal visibility. From Prescott, how well I can see Mt. Humphries (60 nautical miles). If that is good, I look north of them for some other un-named peaks at 80nm. 


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#19 Araguaia

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Posted 13 August 2019 - 11:45 AM

My transparency is excellent in the dry season, dismal in the rainy season.

 

My indications of good transparency vary with the season, but they include:

 

- blueness of the sky in the afternoon

 

- color of the Sun at sunset

 

- extent and detail of the Milky Way by naked eye;

 

- Horsehead and friends - even if I can't see the HH I can judge transparency from how the Flame and IC 434 look;

 

- Galaxy groups, where the fainter members are progressively tougher;

 

- Color in certain objects;

 

- Faint outer spiral arms in the usual suspects.


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#20 CrazyPanda

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Posted 13 August 2019 - 12:14 PM

What is your gut feeling about the typical transparency in your area?

 

What do you thinking are good indications of high transparency?

Late fall I tend to have very, very good transparency. Low humidity, deep blue skies, even as it gets near the sun. Climate change has reduced the frequency of those nights in my area over the last 23 years or so, but *when* I get clear skies, they are usually very transparent. The full extents of M31 are visible when it reaches the zenith.

 

Winter can be hit or miss. After a snow storm, I usually get very deep clear blue skies. On those nights, the full loop in M42 becomes obvious even without a filter. Other times I get high altitude ice crystals that scatter and reflect incoming light, and reflect light pollution back down. On those nights, the full M42 loop is invisible even with a filter.

 

Very early spring is usually poor since snow is melting and forming high clouds and moisture in the atmosphere. Mid spring when the snow is typically gone, I get good transparency, and some of the best summer Milky Way views possible if I stay up late enough. Late spring usually starts the rainy season, and transparency is hit or miss.

 

The best indicator for me is how much scatter I see when the sun is about an hour away from setting. If the western sky behind my tree line is an obvious rich blue color, I know I'm going to have a great night. If it has a dull blue, almost pewter-like color, I'll have a good, but not great night. If it's almost white-washed and doesn't turn blue again until you're 90 degrees away from the sun, it's going to be a poor night (though typically the seeing will be very good on those nights).


Edited by CrazyPanda, 13 August 2019 - 12:17 PM.

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#21 Starman1

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Posted 14 August 2019 - 02:29 PM

Transparency is the primary reason I usually observe at 8350' altitude.  Clearer skies are one of the usual attributes of high altitude observing.

I've observed in enough spots all around the world that I will gladly sacrifice a tad of darkness for improved transparency.

I have two sites I frequent:

one is about 21.4-21.5 with the SQM but is at 8350'

the other is about 21.7-21.85 with the SQM but is at barely 850'.

Site #1 is better for galaxy viewing and though the very faintest stars are less visible, the sky, overall, is less murky and a lot clearer.


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#22 Redbetter

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Posted 14 August 2019 - 03:41 PM

Transparency in the summer in the valley is typically poor.  It might be mostly clear most summer nights, but there is a hot soup trapped in the natural bowl formed between the coastal range and the Sierra.  Seeing mountains 40 miles away as the crow flies is often difficult even though it is technically clear.  Descending from the mountains one can actually see the beige haze layer at about 4,000 feet.  Transparency has been a little better than mormal this year so far in the valley, but there has been a lot of cloud forming in the mountains at night shortly after astronomical twilight ends.  And the seeing has been horrible in the valley this year, the worst I have experienced in the few years I have been here...so really no reason to observe down low unless higher elevation sites are inaccessible or clouded due to weather.  At elevation I can get better transparency at a darker site (unless it clouds over), with better seeing...although still not great with regard to the latter.

 

Dark is great, transparent is great, but if the seeing is poor it is still quite limiting--at least a full magnitude difference for the 20" on the worst nights.  The most favorable conditions are a three legged stool:  sky darkness/transparency/seeing.  I would trade a few tenths of darkness for some good seeing if the transparency was unchanged.  A 0.2 MPSAS reduction in darkness only costs about 0.1 magnitude for stellar limiting magnitude, but poor seeing costs half a magnitude to a magnitude depending on how bad it is.  This is particularly true for smaller and fainter targets once the aperture goes from medium to large.  For apertures of 10" or more seeing has more impact on telescopic stellar limiting magnitude than differences in sky darkness.  Why?  Because as one tries to boost magnification to detect the faintest stars they become extended objects, "pseudo-galaxies", or disappear completely in poor seeing.  Dust lanes in galaxies disappear, knots, bars, and arms are blurred.  Faint inner moons go missing--this latter is even noticeable in small/mid apertures in the backyard.  Poor seeing kills contrast over a wider scale than one might assume. 

 

Now for large targets transparency and sky darkness are the primary considerations and seeing has little impact.  However, for seeing details in moderately sized galaxies, planetaries, and such one needs good seeing as well.  It is reminiscent of the difference of using a larger scope with marginal optics, vs. an incrementally smaller scope with good optics.  Poor seeing makes a "light bucket" of both.


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#23 ChristopherBeere

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Posted 21 August 2019 - 03:52 PM

Transparency is the primary reason I usually observe at 8350' altitude.  Clearer skies are one of the usual attributes of high altitude observing.

I've observed in enough spots all around the world that I will gladly sacrifice a tad of darkness for improved transparency.

I have two sites I frequent:

one is about 21.4-21.5 with the SQM but is at 8350'

the other is about 21.7-21.85 with the SQM but is at barely 850'.

Site #1 is better for galaxy viewing and though the very faintest stars are less visible, the sky, overall, is less murky and a lot clearer.

I was down in New Mexico in 2003, lodged in the foothills of the Sangre De Cristos at about 7500 feet (Star Hill Inn). It wasnt what i would call a really dark site but the transparency from the altitude was exceptional. Did all of the background galaxies in Lyra through a 22.5 reflector.

 

Went down south to Apache Point (the home of the Sloane digital sky survey) next to Alamogordo at about 10,000 feet and despite the local light pollution the sky was good because there was no light scatter from down below at 7k and a steady laminar airflow across the range.

 

Went further to Mayhill upto NMSkies and it was pretty dark out there (class 2/3) but the seeing was insane. Super steady.

 

So, yeah, above 7k things really start getting good despite localised artifical light sources because of the transparency (and in a lot of cases you are above the inversion layer at that altitude so you have cloud cover - La Palma is a good example - which suppresses the artificial light from sea level towns)

 

Of course there is no substitute for truly remote high altitude desert environments in the Kalahari and Atacama deserts where conditions are near perfect and the sky brightness is consistently 22+ at the zenith when the galaxy sets. 


Edited by ChristopherBeere, 21 August 2019 - 04:10 PM.


#24 Eric David

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Posted 21 August 2019 - 09:08 PM

I would also vote for transparency being the most important factor in observing most objects (except planets and double stars, of course).  I live in central Virginia, but my best nights of observing in terms of transparency were in New Mexico.  Just like Christopher Beere said, I also visited the Star Hill Inn in 2003 (August, coinciding with the great Mars opposition) where I viewed mostly with Phil Mahon's 22.5 inch dob.  Spectacular views, the transparency then was superb.  My other great night was in early December 2008, from a point between Magdalena and the VLA, off of route 60.  Even with an almost first-quarter Moon out, I was able to pick out numerous galaxies and had a great view of M42 even though I only had 20 x 80 binoculars and my little Meade 2045 4" SCT with me.

 

Speaking of the Star Hill Inn, I read that it is closed and was abandoned.  Does anyone know the story behind that?  Google satellite images still show the observing deck and the dome for his 24", as well as the cabins.

 

Eric David

Fredericksburg, VA



#25 Keith Rivich

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Posted 21 August 2019 - 10:28 PM

When transparency and seeing come together its magical...Tuesday night at TSP comes to mind!

 

In reality though the two seem to oppose one another. Here in SE Texas transparency is usually abysmal but seeing can be spectacular. When transparency is great seeing usually suffers. 

 

Now, if I had to pick...where I usually observe I would take seeing over transparency. On my dark sky trips I much prefer transparency. I can tailor my observing list to take advantage of either. 


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