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Moonshane

Tell us your sky quality

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Here's mine...

1866797165_SkyZenithBrightness52N1E.jpg.4a0e0d58cf558fa5f0b87e4e973488b5.jpg

.....though my iPhone DSM app has given several readings better than SQM 21.3, so potentially Bortle 3 (21.3-21.5), but then the iPhone app is likely not reliable.

Cheers, Geof

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2 minutes ago, DaveS said:

Map says 21.66 and Bortle 4 where I am now.

I'm at the wrong end of the county.

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3 minutes ago, Demonperformer said:

That is always a possibility as I have never had anything to which to compare it. Possibly the proximity of my two nearest streetlights are having a disproportionate influence. When I put my Ne3 filter in front of the lens (I did this to measure the sky brightness for each of my filters to enable me to calculate appropriate sub-lengths) it goes way down to 23.0. So if my meter is reading 1.5 mag too bright, then that would mean I would be getting a sky brightness of 24.5 with that filter. I think that might be a little too hopeful!

Not really if you think about how magnitudes are calculated - it is ratio of brightness to a reference point (0 magnitude). Just because natural sky has brightness of mag22 - that does not mean narrow band can't have much lower brightness.

Simple example would be as follows: let's take 400-700 spectrum and we approximate uniform brightness over that spectrum. Full spectrum under consideration contains 300nm. Now take 3nm narrow band filter. It will collect x100 less light. x100 is 5 magnitudes of brightness down. Such filter would measure mag27 if our source is mag22.

Now take into account that light spread is not uniform and that some wavelengths carry more brightness than others - you can easily see that this difference can be over 5 mags for narrow band filter.

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Sorry for my ignorance I have tried all the overlay buttons and different combinations and cannot get the Information everybody else is. Can some kind person give me a walk through please

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Posted (edited)

Zenith sky brightness information

Coordinates 
SQM 21.73 mag./arc sec2
Brightness 0.220 mcd/m2
Artif. bright. 49.1 μcd/m2
Ratio 0.287
Bortle  class 3
Elevation 154 meters
 
Not too bad in North Devon! As well as the Sky Quality I have also done a quick check on the Sky Quantity and as far as I can tell it goes all the way around the house and all the way up too.
Happy New Year to all
Regards, Hugh
Edited by hughgilhespie
security
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I did it on my phone as follows.

Click the link and then keep double clicking to find your street / house (like Google Earth)

I then double tapped on my house (well, where my house is) and the box pops up. 

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Such things are better in Ireland?

We get 21.1 where I live (alt. 65 m latitude 53N on the East coast 30 miles S of Dublin) i.e. Bortle 4..

The deeper Wicklow Mountains get down to 21.7 at 350m elevation with fair vehicular access (Aghavannagh area) but more oiks driving around at night

Finally down in Kerry there is the Cahirdaniel area of the Dark Sky Reserve (on the Ring of Kerry) where 21.97 (Bortle 2) at 50m elevation is available when the weather cooperates - which is rare.

Tony

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2 minutes ago, wookie1965 said:

Sorry for my ignorance I have tried all the overlay buttons and different combinations and cannot get the Information everybody else is. Can some kind person give me a walk through please

Exactly the problem I had. Simply click your mouse on the desired location and the display pops-up.

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In fact on my laptop, the box comes up every time you double click or single click anywhere

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Posted (edited)

Thank you just found once you have located your position if you click on print it opens a page in the browser and you can take a screenshot from there. Now what do all those numbers mean.

Screenshot_20190102-165338_Photo Editor.jpg

Edited by wookie1965
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Actually, according to the map, down the road a bit (Not saying how far or what direction) the West Bexington beach car park hits 21.72, or Bortle 3 with a deep sea-horizon

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Posted (edited)

The map is a little optimistic. The best I have measured with my SQM is 21.6, though 21.5 is not uncommon when the moon is down.

sqm.png.b304657c267ab3321a926cc25afc1c21.png

Though I do have a 360° view and 200+ clear nights a year :)
And hours of full darkness during the summer :) :)

 

For reference, here's the data for the Calar Alto observatory. It's about 50km from my place and is home to the largest telescope in mainland Europe. I was up there last June and I was surprised that the inside of the main dome was illuminated. They do get a bit of LP from Almeria city and their numbers are theoretically a bit better than mine. However being 7000 feet up, they have much steadier skies which seems to count for a lot.
1825385465_Screenshotfrom2019-01-0218-07-32.png.6e20022a8fd6853cee9be4b46241d03f.png

Edited by pete_l

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Posted (edited)

Ooh! This seems overly complex!  Not in its actual complexity but in its necessity.  I've seen statistics and I've seen dark sky charts and don't really find them to be of much value. Dark sky charts for example show my site to be questionable. The reality is that I get some excellent seeing, and on occasion some great transparency. I can easily see M31 with the naked eye and on transparent nights mag 6 at the zenith. The milkyway is generally visible from my garden on pretty much any clear night. I don't really worry myself about what my site is determined to be by any source other than what I personally experience. Sometimes, thinking too long on the negatives can negatively affect our joy. 

The thing that bothers me most are aircraft vapour trails, which utterly destroy good seeing and transparency. I can't wait for the next Icelandic volcano to erupt and those monstrous flying polluting machines get grounded again!

Edited by mikeDnight
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Great site.. thank for sharing....

Heres my report...

IMG_7068.JPG.6c382fef60b8ee084426981cbed7ea29.JPG

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Mine is Bortle class 6. I want /need to move to Cornwall!!!

Alan

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1 hour ago, jetstream said:
SQM
21.97 mag./arc sec2
Brightness
0.176 mcd/m2
Artif. bright.
5.24 μcd/m2
Ratio
0.0306
Bortle
Elevation
345 meters

 

So far I've measured only 21.8 repeatedly and as very few 21.9's.

Those are really impressive results. :)

What time of the night do you take the readings?

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1 minute ago, Beulah said:

Those are really impressive results. :)

What time of the night do you take the readings?

Whenever I'm out.. I checked many times over the past few years and typically the highest readings are after the snow and ice are out. SQM-L readings vary in my experience. I have recorded at least .25mag difference between the MW and the rest of the sky, sometimes .3-.4 mag.

I always warm up the meter and take many readings. NELM with my eyes have gone 6.6-6.8 at best so far.  These days I use the MW as a guide- how chiseled the features look.

I see we have similar skies.

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Posted (edited)

Here's my back garden:-

Zenith sky brightness information

SQM    19.09 mag./arc sec2
Brightness    2.49 mcd/m2
Artif. bright.    2310 μcd/m2
Ratio    13.5
Bortle    class 6
Elevation    14 meters

And here's where I went last night and will be going again tonight in the Brecon Beacons:-

Zenith sky brightness information

SQM    21.76 mag./arc sec2
Brightness    0.213 mcd/m2
Artif. bright.    41.7 μcd/m2
Ratio    0.244
Bortle    class 3
Elevation    378 meters

It's worth the 1 hour and 20 minute drive.

Edited by David Levi
My home reading was way out at 20.8, Checking the map again has given a more realistic 19.09. I can't see the Milky Way from my house.
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image.png.1d25c3ba4afba04dc1f90f83536ff40f.png

It maybe a bit better now as recently the street lights around here have been replaced with LED fittings

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That online mapping resource is misleading, inaccurate and delusional and certainly should not be used for quoting as a reference in any observers reports. If I was to quote from this map based upon locations I go observing within then I would be implying SQM 21.88.  Whilst I gain 21+ mag skies, this particular reading is quite simply - at least so far - untrue. A Unihedron SQM-L (check FLO) is a highly useful tool for measuring / assessing an average and monitoring sky brightness over a given period during your observing session. Anything else is quite simply for the birds, at least in my opinion.

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Probably fairly accurate, except I have some local sources which are close that affect the low down badly, especially to the northeast.

image.png.007828f5e32766d976c78ec16dbc777e.png

The local 'dark' spot is also classed as Bortle 5 but is VASTLY darker.

 

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37 minutes ago, scarp15 said:

That online mapping resource is misleading, inaccurate and delusional and certainly should not be used for quoting as a reference in any observers reports. If I was to quote from this map based upon locations I go observing within then I would be implying SQM 21.88.  Whilst I gain 21+ mag skies, this particular reading is quite simply - at least so far - untrue. A Unihedron SQM-L (check FLO) is a highly useful tool for measuring / assessing an average and monitoring sky brightness over a given period during your observing session. Anything else is quite simply for the birds, at least in my opinion.

lol!

I agree Iain, while the maps can be accurate it is not necessarily so. One map indicates my current place as quite a bit brighter than my remote dark sites-yeah right... the SQM-L dispelled this (&NELM) and saved me many miles of driving. I have mapped a huge area in my travels and its all the same, including my home.

A very useful thing the SQM-L does is find the edges of darker places, even near towns and cities.

A truly good test of skies is the ability to see M33 IMHO.

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Our skies just outside Mold in Flintshire are pretty good tonight. I'm off out to photograph the Pleiades. 

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