Sky Quality Meter.

[Knight of Clear Skies]

Is there an android version of this app?

Unfortunately not, I think because calibration of all the different cameras in Android devices would be a nightmare.

[steppenwolf]

Unfortunately not, I think because calibration of all the different cameras in Android devices would be a nightmare.

Yes, that's exactly the problem.

[Scott]

Although I've seen these regularly in the hands of our guests, I've never had my own... until now that is, because two kind guests, John and Viv, kindly sent me one as a present yesterday. I was thrilled to bits because these devices are so useful, espeically to the imager. Many members will know of them, but for those who don't they look like this;

You simply hold them in this position, pointing to the zenith, and press the button. A sensor on the top measures magnitudes per square arcsecond. If this sounds a bit arcane, don't worry. It appears as a number on the digital scale. The scale is logarithmic so is highly compressed by the time you are in dark sky territory. A value of 21 is roughly where good sites begin and the best reading I've ever heard of was 22.1 in the Australian outback. Sky and Telescope suggest that 22 is generally considered to be the level found under a totally dark site on a moonless night. They discuss the use of the meter here; http://www.skyandtelescope.com/astronomy-resources/rate-your-skyglow/

Last night, with twilight still clearly around, we started at 21.1 and were at 21.6 by midnight. The best anyone has recorded here is 21.9. If I ever see 22 I'll throw a party! (In the morning...)

One use of the meter is to scout around for the darkest site in your area.

For me its usefulness arises from the fact that, when imaging at the PC screen, it is impossible to assess the current sky quality until your eyes are dark adapted - and that takes ten minutes as a bare minimum. With the meter you can check the sky reliably and immediately and so decide whether the clouds have scuppered you or not.

The manufacturer's website is here.  http://www.unihedron.com/projects/darksky/

Very highly recommended.

Olly

I hope for your guests sake this never happens.....you'll be kicking them off your rig(s) 

[Macavity]

Yes, I think I am happy with consistency, rather than absolute calibration.

Once I have a 16MHz Arduino Nano, my DIY version should suffice?

UK Mouser still have a lot of the side-view versions of the sensor available:

http://uk.mouser.com/ProductDetail/ams/TSL237SM-LF/?qs=sGAEpiMZZMu3iiO3VE9n1PeNxttju81LyfRmvn2WZIE%3d

Like Lowjiber (above), I have a fair variation in sky brightless. But more

"Welsh community centre" security lighting than Las Vegas strip!  lol

I may well add a lens to focus the SQM... mount it on the scope even?

The graph relationship (mpsas vs nelm) shown seems to be very much

consistent with (my) various guestimates / and measurements though.

Ever reassuring to see experiment vaguely matching prediction? 

[jetstream]

Oh, that fast! Is it the same time for every magnitude?

And as Per sais, great DIY-project... even though i haven´t used mine that much

/Daniel

My SQM-L is faster the brighter the sky. The darkest I've recorded here was 21.8, with 21.7 being a very consistent reading. At this level of darkness it takes many seconds for it's reading.

I always give it 3 or so warm up readings first and then start measuring, mine says it is calibrated from the factory and it appears very accurate.

[jetstream]

Can we change the above to SQM-L and drop the "W" ?  thanks mods

[Gfamily]

The Mid Cheshire Astro Soc met last Thursday and had an interesting talk about light pollution from Malc Beesley from Macastro. He's part of the MyDarkSky project, which aims to allow followers to plot their own SQL and NELM measurements on Google Maps, with the hope that it will be a resource for locals and visitors, and also maybe a campaigning tool if a locally dark sky site is threatened. 

The site is currently offline (it was up for  a couple of years, but has been down for the last 12 months), but it is now being re-hosted, and will be available on 

http://www.mydarksky.com/defaultsitein due course. 

The maps will look like this, and the hope is for coverage to be national or wider

[Demonperformer]

Got one of these babies at the beginning of the year.  Really jealous of your readings.  I usually get down to about 18.5 - although, if I go inside and close the curtains I can get down to 22.1.  So all I need to do is to work out how to get the sky into my lounge ... (probably easier than getting the streetlights switched off)

[Beulah]

Good readings for the Peak District - might be worth exploring dark sky park status from the IDA.

[Gfamily]

Good readings for the Peak District - might be worth exploring dark sky park status from the IDA.

There's a lot of intrusion from the surrounding cities - and Peak Star Party (at Shallow Grange) was affected by flood lighting of local quarries. More affected by rain as it happens, but still, the skies can be significantly affected by LP

[davedownsouth]

I have got the one you've got Olly and find it very useful.  Best result I have ever got was at Turf Hill in the New Forest last New Moon.  At ~1:30am I got a value of 21.1, and this took ~2 - 3 seconds to registrar (at 20 or less it is <0.5 second, pretty much instant).  Closer to home, the best I have seen is 20.8 in East Tisted, which is just 4 miles down the road from me.  Would love to see what a 21.5 plus site is like  

[m.tweedy]

Iain have you ever done a reading at Derwent

[ollypenrice]

I have got the one you've got Olly and find it very useful.  Best result I have ever got was at Turf Hill in the New Forest last New Moon.  At ~1:30am I got a value of 21.1, and this took ~2 - 3 seconds to registrar (at 20 or less it is <0.5 second, pretty much instant).  Closer to home, the best I have seen is 20.8 in East Tisted, which is just 4 miles down the road from me.  Would love to see what a 21.5 plus site is like

It's nice! (It would be nicer still to have one tonight but there seems to be a mania for thunderstorms at the moment!!)

Olly

[laser_jock99]

I have had one a couple of years and find it interesting to see how much the readings can vary from session to session. Typically at the obsy site in Mid Wales 21.2 to 21.6 and rarely 21.8

I think a lot of this boils down to moisture/transparecy. On ultra clear nights the readings get lower- possibly because starlight is contributing to the photon count.

It also depends on where you point the device- ideally the Zenith, but if The Milky Way is overhead you'll get a false reading.

The SQM can also be used to evaluate sites on a cloudy night since they are very good at measuring the illumination on the underside of the cloud base.

Interestingly from my obsy site on cloudy night I get a reading of >22 simply because there is no light either from stars or local light pollution. So the blackness of the clouds might be a better indication of light pollution levels?

To illustrate the point see how bright the background sky is compared to the passing clouds in this video:

Maybe we are measuring the wrong thing?

[pete_l]

Maybe we are measuring the wrong thing?

That's the problem. A real SQM measurement would only look at the gaps between stars, not a starry sample of the night sky.

I have a feeling that to do so would require a very long F/L refractor and to compare sky darkness with the light intensity from a defocused known brightness star. All sounds a bit too difficult.

Personally I'm satisfied with my SQM and the ability to just look upwards and think to myself: Yup, that's pretty dark!

[jetstream]

At one of my dark sky sites the clouds will pick up the town's light dome 15 miles away- I now use this as a guide along with the SQM. The sites I use are the same darkness as laser_jock99's and vary almost exactly the same. The darkness changes with the seasons and on a truly dark, transparent night the Milky Way is a sight to behold.  The SQM is a valuable tool for astronomers and can identify dark zone edges in towns or cities in addition to finding remote dark sites.

[scarp15]

Iain have you ever done a reading at Derwent

I would like to implement a succession of readings Michael, at both Millshields and Pow Hill, which I believe is regarded as being perhaps a little darker. Infrequency of opportunities to observe at Derwent (last visit the cloud stubbornly remained, in defiance to BBC weather) compared to two other sites that I observe at with a little more continuity, has meant that at this location, I have so far not taken a reading. Actually last time I did get to observe at Derwent during a club meet, to be honest I simply forgot 

It has begun to become more of a routine ritual since then though, so come the Autumn can make a start on logging readings. 

[Thonolan]

I love my SQM-L, and I'm regularly measuring the sky darkness (or brightness) during my observing sessions. My best readings are around the 20.90 mark which is not bad I suppose, even though I have to suffer some terrible medieval style street lamps nearby. Most nights it reads between 20.80 and 20.85. Waking just one kilometre away from the small village the sky darkens to 21.20, but there's nothing like the comfort of a nice home observatory.

[jonathan]

This sounds like something I could get into, I am curious about all the different versions though (USB, LAN, etc) - are they mostly for automation, the only one I would need for handheld use being the -L (lens) version?

What about things like firmware - does it have such a thing, and is there any chance of it being outdated (or is it possible to update for better readings, etc)?

 

[Jkulin]

I use the "Dark Sky Meter" for my iPhone and it appears pretty accurate, although I very much doubt that it is as good as the proper jobs.

When I compare against Clear Outside and the app, they really are very similar, more info: - https://www.darkskymeter.com/

[pete_l]

With the next full moon coming up on Friday (Jan 10) it would be interesting to use that as a "standard candle".
If everyone who has a clear sky and some means of getting a number for sky brightness pointed their device at the Moon on that night, we could get some sort of idea how much variation there was between different instruments.

[sloz1664]

7 hours ago, pete_l said:

With the next full moon coming up on Friday (Jan 10) it would be interesting to use that as a "standard candle".
If everyone who has a clear sky and some means of getting a number for sky brightness pointed their device at the Moon on that night, we could get some sort of idea how much variation there was between different instruments.

The "big if" is the clear night, unfortunately