Unihedron Sky Quality Meters

[FLO]

Our first delivery of Unihedron Sky Quality Meters is scheduled for delivery tomorrow. Two models are available: The Unihedron SQM L with a lens for a narrow field-of-view and the Unihedron SQM-LU with a lens and USB connection for continuous measuring of sky brightness.

Measures the brightness of the night sky in magnitudes per square arcsecond.

Designed by Dr Doug Welch and Anthony Tekatch.

[Earl]

Handy device, do you know if they are Hub friendly?

I have had issues with some devices been plugged into hubs as they prefer to go direct into the PC (My Mbox audio device specifically stated in the manual it had to go direct into the PC and not into a Hub).

I have no ports free atm

[FLO]

Handy device, do you know if they are Hub friendly?

James will be playing with testing a SQM LU this weekend so we will know soon. (SteveL uses one, he might know if you need an answer today).

HTH

[SteveL]

I havent had any issues with them in a hub or direct, but as we all know, that doesnt mean anything on someone elses system

[FLO]

I havent had any issues with them in a hub or direct, but as we all know, that doesnt mean anything on someone elses system

Thank-you Steve

[Pingster]

Well done FLO been wantin one for ages (searches for credit card).

[MikeWilson]

Awesome!

Can I rent one? :-)

All the best,

Mike

[pete_l]

Is the LU version weatherproof - so you can leave it outside, maybe mounted with your weather sensors? Or do you need to dash out and cover it up when it starts raining?

[SteveL]

The LU is not weather proof. You would need to build or buy a cover for it (which FLO might want to think about adding!)

Sky Quality Meter - Weatherproof Housing

[FLO]

The LU is not weather proof. You would need to build or buy a cover for it (which FLO might want to think about adding!)

Oops! Didn't think of that. We'll order some then add it to our website tomorrow

[hunterknox]

If anyone's buys an SQM and wants a place to store their readings we're only too happy to oblige: www.mydarksky.com. If you only have your eyes to verify how dark your skies are we'll happily take readings from those too!

[pete_l]

Oops! Didn't think of that. We'll order some then add it to our website tomorrow

Now if you could get a little rain-operated umbrella that opened automatically when necessary, I'd buy one just for that

[Beulah]

Hmmm, I'm thinking of getting one.

[Pingster]

Just ordered one along with a coma corrector. Don't let me down guys!

[BlueAstra]

Surely it doesn't need a coma corrector

[Pingster]

Hahaha! The coma corrector will fix my Nagler 31mm in my F4.5 16in Dob. Last week i was viewing clusters and noticed they looked horrific in the Nag, but in the 17 ethos they were beautiful. Coma effects low powers a lot! Funny how i did not notice it so much before as i focus on the target, globs and nebs. Looking just at clusters gave me a coma shock!

You know you are addicited to astro when you get a sky meter. My misses will kill me!

[Pingster]

Fantastic service, next day delivery. I got a reading of 17.12 in my SE London Garden, Full moon was obsured by clouds. Now how do i convert this to VLM?

[pete_l]

Fantastic service, next day delivery. I got a reading of 17.12 in my SE London Garden, Full moon was obsured by clouds. Now how do i convert this to VLM?

There is no "official" method of deriving one metric from the other - since VLM is dependent on the abilities (and imagination ) of the observer.

[edit. If you really, really want to do conversions, here's a chart I made for my website that uses one of the equations.

Personally, I find it gives results that don't match with my reality. For instance My "home" readings are in the upper 19.8 - 19.9's which the equation gives as over Mag. 5 - but the sky is nothing like dark enough to see dimmer than Mag 4.5 stars.

There are equations you can look up with Google and pages such as this one that offer some ideas. But remember that VLM is generally measured at the zenith, to give the best possible answer, whereas you can point your SQM anywhere.

My view is that SQM reading are roughly like this:

18 - 18.99 Not great

19 - 19.99 OK-ish

20 - 20.99 Good

21 - 21.99 Excellent

22 and above: unbelievable, literally: I don't believe them <Richard Wilson mode off> simply because the sensor used in the meter is operating outside its calibrated range for most SQM values we get, but it's waaaaaaaaaay outside its range at these exceptionally low levels. Above SQM=22 I'd reckon that factory variance and component tolerances probably affect the readings more that the light levels do, so no two meters would produce the same results for very dark values.

[Pingster]

Wow thanks for the fast reply! Saved to iphone for darksite quick reference xD

So my garden works out to be 3.2ishVLM.

[pete_l]

So my garden works out to be 3.2ishVLM.

Only last night. Every day will be different.

[ixalon]

I've finally got my SQM-LU from FLO all set up :-) I put together a DIY weatherproof enclosure for it out of 50mm white waste pipe accessories, the glass from cheap-o 50mm UV filter and some marine silicone sealant, and it's been taking measurements for a week now.

I've got them graphed at:

Sky Quality Ixalon.net

Interesting to see just how varied the sky darkness is over a night.

[MikeWilson]

That's remarkably interesting. Thanks for sharing, Chris.

It's interesting to see how quickly sunset/sunrise effects sky quality as well as how quickly we get to astronomical dark (and how much of it we have!). You've got some very dark skies there too, I'm jealous!

[ixalon]

Yep, they're not bad considering how close to Edinburgh I am. The max I get when very lucky appears to be around 19.5 MPSAS - that is pointing at the darkest part of the sky though.

I'm setting up an all-sky cam as my next pet project, so will be interesting to mark the 20 degree circle the SQM is measuring to see if there are any obvious causes of the fluctuations (e.g. bright objects in or near the circle).

[MikeWilson]

Now that would be a very good idea, please let me know how you get on - I'm intrigued by the fluctuations during the night too.

[hunterknox]

There's an interesting post on Steve Owens blog about trying to find when ligh pollution becomes the limiting factor at a particular location. I might have a go at repeating his experiment the next clear night we get.