Author Topic: Highest SQM Reading  (Read 471 times)

soamezquipack

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Re: Highest SQM Reading
« Reply #15 on: January 12, 2018, 09:52:31 AM »
Kent,

Any time you are in the neighborhood, a 12" Dob, a 5" Tak and a 3" Tak plus a ton of eyepieces and filters and toys are at your disposal

olnceratge

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Re: Highest SQM Reading
« Reply #16 on: January 12, 2018, 09:55:18 AM »
I can only get SQM readings of 21.3 max about a 50 minute drive from home (ride will be provided) but hey, it ain't that bad

scenunhadef

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Re: Highest SQM Reading
« Reply #17 on: January 13, 2018, 01:30:06 AM »
Kent,

I am liking what I am reading here

Gregory Plummer

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Re: Highest SQM Reading
« Reply #18 on: January 16, 2018, 11:35:58 PM »
Quote
Kent,

Any time you are in the neighborhood, a 12" Dob, a 5" Tak and a 3" Tak plus a ton of eyepieces and filters and toys are at your disposal

Thanks, Nick. I would love to visit. I followed your thread on your new FS128. Congratulations! Of course, you are welcome here any time as well.

Zack Tucker

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Re: Highest SQM Reading
« Reply #19 on: January 22, 2018, 08:39:00 PM »
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Kent,

I am liking what I am reading here

The area really is beautiful but they call it "poverty with a view." Wages are very low and cost of living is quite high though not as high as California. We get some snow in the winter but it isn't too bad most winters. Phoenix is 2 hours away down the mountain and is 20-25 degrees warmer. Nice in the winter. Sedona, voted by many as the most beautiful place in the US is only 20-30 miles away and is 15 degrees warmer so we hike there a lot in the winter. If Flagstaff gets too hot in the summer and it only rarely reaches 90 (sorry Fahrenheit) then we can hike further in the mountains. 15 minutes higher and it is 10 degrees cooler. Grand Canyon is 70 miles north and all the wonderful National Parks of Utah are close as well. A dream come true for us. I wasn't even thinking of the dark skies and astronomy when we moved here. That has opened up a whole new world for me. I enjoy all the hiking too of course. And if I miss the big cities and art, Los Angeles, San Diego and San Francisco are not too far away.

Calvin Dolla

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Re: Highest SQM Reading
« Reply #20 on: January 23, 2018, 07:10:00 PM »
Yup, the whole region seems very attractive...

akbrevecop

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Re: Highest SQM Reading
« Reply #21 on: January 23, 2018, 07:16:52 PM »
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@ Kent,

21.2 from you back yard?

@ Jetstream

21.8 from your home???????

Where do you guys live & are there any plots of land nearby???

I'm in NW Ontario very near the border and there are dark skies like this for 100 miles high by 250 miles long... at least-and then it starts like this past Thunder Bay again for hundreds of miles... The portion of Rainy Lake I live on overlooks Voyageurs National park in Mn...

I love this site Nick and it shows what I mean if you zoom in around here.

Gerry

https://blue-marble....ightlights/2012

Trendsetters Branch

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Re: Highest SQM Reading
« Reply #22 on: January 26, 2018, 12:47:28 AM »
Gerry,

Is there a super envious emoticon here somewhere and I missed it?

I just can't get over the number... 21.8... This is an astronomer's hog heaven....

John Fimbres

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Re: Highest SQM Reading
« Reply #23 on: February 02, 2018, 02:57:00 PM »
Here is an article from Brian Skiff at Lowell Observatory:
http://www.astropix....y/skybrite.html
The gist is that 22.0 is about as dark as it can get on Earth.
Because of differences in calibration between units, it's possible for someone to get a 22.1.
Anything darker is because:
--sky is being blocked by buildings or nearby trees
--there are clouds in the sky (the darkest sky is with full cloud cover at a pristine site)
--the SQM is malfunctioning

I own both units. I didn't even get 22.0 at Mauna Kea with the wide SQM, but I've seen 22.0 at Kitt Peak at the zenith with a narrow version.
IF the Milky Way is on the horizon all the way around (NGP above), the narrow version will likely give you a slightly darker reading at the zenith than the wide version
because more sky below +50° is measured. If the Milky Way is overhead, the wide version may actually measure darker because the narrow version will see
only Milky Way in its view.

I have 3 local sites and the wide SQM gives me annual ranges at each site, heavily dependent on weather conditions over the SoCal cities, of:
Closest site: 21.1-21.4
middle site: 21.2-21.6 (occasional to 21.8 or darker)
far site: 21.3-21.7

I have some desert sites with lower altitude and transparency with readings of 21.4-21.8

Those sites are all in SoCal and fairly close to LA as the crow flies. Sky transparency is heavily determinant of a dark reading. Sky glow over the cities is heavily dependent on clarity of the air.

My darkest readings in SoCal ever was 21.95 at the middle site. It was just about the only point in SoCal above clouds that were 6000' thick from the ground up.
My darkest reading ever was a 22.0 with the narrow SQM at the zenith at Kitt Peak. The wide SQM measured 21.4 simultaneously because it also caught a lot of the glow from Tucson.
The 21.4 corresponded to my visual evaluation of the sky. The 22.0 did not. I have been in MUCH darker skies.

ziecouvicog

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Re: Highest SQM Reading
« Reply #24 on: February 02, 2018, 03:23:45 PM »
It's worth pointing out that with the wide-field SQM, it's easy to get over-dark readings because of obstructions in the field of view, including trees behind your back that you're not even aware of. The total field of view is almost 180 degrees, although the central 90 degrees of that is much more sensitive than the rest. Still, that means that any tree that's as tall as it is far away will affect the reading.

Tom Durham

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Re: Highest SQM Reading
« Reply #25 on: February 02, 2018, 08:00:16 PM »
Quote
It's worth pointing out that with the wide-field SQM, it's easy to get over-dark readings because of obstructions in the field of view, including trees behind your back that you're not even aware of. The total field of view is almost 180 degrees, although the central 90 degrees of that is much more sensitive than the rest. Still, that means that any tree that's as tall as it is far away will affect the reading.

+1 on what Tony says. I bought the wide field SQM (because it was a little cheaper) and was getting readings of 23.0-25.0 because my observatory is surrounded on three sides by ridges going up to 25* e-w and 30* n. I contacted the vendor (Agena Astro) and explained my problem and they graciously allowed me to return the SQM and get an SQM-L. Now my readings are 21.30-21.70 depending on the night.

tradneedcoegen

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Re: Highest SQM Reading
« Reply #26 on: February 09, 2018, 10:14:10 AM »
Response curves for the SQMs,
http://unihedron.com...y/fovcurves.jpg
Full width half maximum response:
SQM +/- 45° At +/-60° (120°), response is pretty much gone.
SQM-L +/- 10° At +/-20° (40°), response is gone.

Aimed at the zenith, you should have a clear sky down to around +30°to 40° to get an accurate reading with the SQM.
For the SQM-L at the zenith, you only need clear skies down to +70° to 80°