Sky brightness and sky quality meters

[Mark at Beaufort]

I live on the outskirts of the City and my east/west horizon is free from light pollution. I am interested in obtaining a reading of the sky brightness and I know that you can purchase a sky quality meter which you point at the zenith.

Has anyone used one of the products and what is your opinion?

I have tried to read up on this topic and as I far as I can tell the darkest locations in the world has a reading of 22 - Arizona I expect!!. How does this relate to star magnitude at a giving site? What would be a typical reading for a good site in the UK and again how does this relate to star magnitude?

I would be interested in members knowledge and views.

Mark

[DrRobin]

Hi,

You can use a digital camera to measure your 'Visual Limiting Magnitude', I did mine using the links in the following post and it came out at 5.5, about right for my home location.

http://stargazerslounge.com/topic/153613-measuring-your-dark-sites-skies/#entry1553953

Robin

[Mark at Beaufort]

Thanks for that Robin. I have a Canon 50D DSLR so I will give it a go.

Mark

[Mike73]

I bought a SQM meter about 18 months ago with the intention to use it for finding good dark sites and as far as thats concerned its been a very good investment.

I expected the results to be pretty depressing after looking at light pollution maps but have found the skies darker than those maps suggest.

Meter reading can be thrown off in the summer / autumn if you point it at the zenith and the milky way but I usually aim it just off the milky way to get a better reading. I've also found that it will give you a lower reading if the sky transparency is poor, last night I was at my local dark site where its usually around SQM 21.3 but it was only showing around SQM 21.1.

I take it you've seen My Dark Sky Mark? A lot of SQM and NELM reading for the UK on there.

My best reading in the SW is SQM 21.83 but theres darker in Scotland and probably Wales.

I always take a SQM reading after every sketch and then the next day I convert it from MPAS (SQM) to NELM using this page.

SQM meters are nice little luxuries to have but for me it was money well spent.

[Mark at Beaufort]

Mike that is an excellent reply and 'mydarksky' site is very interesting - I had not seen it before. So using your example of SQM 21.83 that converts to a magnitude of 6.55 which is about the limited of the normal human eye. I notice that FLO sell the meter for £108 - http://www.firstlightoptics.com/unihedron-sky-quality-meters/unihedron-sqm-l-sky-quality-meter.html - is this the one that you have Mike?

Mark

[Mike73]

Yep thats the one Mark.

Its not cheap but the the type of observing I enjoy is all about dark skies, before I got it I used to drive 40 minutes to a dark site but using Google Maps and the SQM meter I found a place just 15 minutes from home which is still around 21.4 SQM which is a lot better if the weather forecast isn't perfect.

[Wyvern]

Mike,

Thanks for the link for converting SQM readings to NELM.  I'd been trying to find such a simple conversion site with out any luck, but you've shown the way.  Will get some serious use !!!!  Ta

[swamp thing]

Great thread, very interesting stuff. This is an area of great interest to me.

Thanks all