Sky Quality Meter
Published on Oct 9, 2007 at 12:48 pm.
2 Comments.
Filed under observing.
A few days ago, I wrote about light pollution. One of the classic ways to figure out your seeing conditions and to monitor light pollution is simply to figure out the dimmest star that you can see. But, this is sometimes a subjective task. Also, because the atmosphere dims the light of the stars, the results can really only truly be compared between locations if the constellation is observed at the same altitude in the sky. The altitude of the constellation depends upon latitude and time of the observation. Now, this does not mean that the data is useless. But, it does mean that you need to be a bit cautious in interpreting that data. However, a while back I ran across a device that seems to take a lot of the subjective qualities out of sky brightness determinations. It is called the Sky Quality Meter, from Unihedron.
For most people, just looking up at the sky is sufficient to tell if it is dark enough to see things. But, for serious amateur astronomers, you may want to have some quantitative measure of the sky conditions. Often if you are looking for the dimmest objects, you will have a tough time if the sky is too bright. If you are working on an observing project, like one of the Astronomical League’s projects, then you don’t want to waste your time trying to find objects that are too dim to see in whatever the current sky conditions might be. But, how do you really know what is too dim? That would be where something like this might be useful. You might start off observing a number of objects that have a variety of surface brightnesses. Then, record your observations and the sky brightness at the time of observation. You might rate visibility as good, marginal, or none. Do this over a range of nights and sky brightness conditions. Next, you can tabulate or plot the results. Then, on future nights, you can pull out the sky meter, measure the sky brightness, and look at your data to decide what objects are too dim to try to observe under those conditions. This sort of device might also come in handy if you are doing astrophotography. It might be useful to know the sky brightness to determine the optimal exposure.
Now, at a price of $120, this is a bit much for the casual amateur. After all, if most of what you do is just go out and look at the Moon, planets, or a handful of the brightest objects, then there is really no need to buy one of these sky meters. But, I know a lot of amateur astronomers who take their work seriously and spend thousands of dollars on their astronomy avocation. For them, this might be just the right gadget. As I said, if you are working on an observing project that requires you to observe a number of very dim objects, then it might be very helpful to have solid data to make a reasonable guess as to what is too dim to see on a given night. After all, the sky brightness changes continually as the Moon’s phases change, light is scattered by atmospheric haze, or light pollution changes as outdoor lights go on and off. Often amateurs carry their telescopes to different observing sites, too, with different ambient light conditions. Again, such a device as this meter might be useful if they want to save time and frustration when looking for the dimmest objects possible.
But, when I saw this thing, I immediately thought of other uses. This is a great educational tool. It can be used to measure changes in sky brightness for a laboratory exercise for students. They can have an actual measure of sky brightness changes over the course of a lunar cycle. They can also monitor sky conditions under different types of outdoor lighting configurations if you want to teach about light pollution. You can also monitor any changes in sky brightness and correlate those changes with sunspot activity. So, this seems to be me to be a great teaching tool, and there are a variety of different projects that you can do with it.
-Astroprof
Astrolink [International Edition] » Blog Archive » Astrosphere for October 9th, 2007 on October 9, 2007 at 4:08 pm: 1
[…] First up, Astroprof reviews a device that can help you measure just how light polluted your skies are. […]
Paul Moss on October 10, 2007 at 3:35 pm: 2
thanks for this review, I am very active here in New Zealand campaigning for dark skies and open space, energy saving public lighting, and generally using astronomy to raise awareness for environmental issues. I want one of these meters!!! I plan to use the data to create maps, as I am a digital cartographer, with all the necessary boundaries, points and software platform.
I have aready prepared maps using a proxy of human population density, and I believe that going out and measuring the actual values will enable me to fine tune that, and perhaps create a new proxy, to predict the areas that we cant measure. I will put that up on my website called Sharing Space at http://www.astronomy.net.nz cheers Paul Moss