Can I See the Stars?
For the first time since this year’s GLOBE at Night started I have a clear sky, so I popped out into my back garden to find Orion and measure how light polluted my sky is.
I live in Glasgow, on the south of the city, in an area that is probably fairly described as being on the urban / suburban interface, so my sky isn’t great, even when clear. That coupled with regular cloud cover and tall trees to the south mean that my garden is far from ideal for stargazing. Even still, the small patch of sky visible to me never fails to impress on a clear night, even through the light pollution. At this time of year (late spring) Orion sits nicely in the space between the nearest buildings and the trees.
And tonight is no exception. Orion is standing proudly overhead, and using the GLOBE at Night star maps I could make out that my sky is magnitude four. Not bad, but not great. There are probably two or three times as many stars visible here as would be seen in the city centre of Glasgow, but go out into a truly dark site, such as Galloway Dark Sky Park, and you’ll see ten times as many again.
Sky Quality Metre
Using my nifty little Sky Quality Metre I can get a much more accurate measure of how bright my sky is. The metre gives a reading of magnitudes per square arcsecond (i.e. brightness per unit area in the sky). The readings, if taken of the zenith point directly overhead, range from around 16 in a bright city up to 23 in a very dark place indeed (Galloway Dark Sky Park, at the darkest part, registers 22.7 magnitudes per square arcsecond). The sky above my garden at the moment is reading 18.3, which is much better than I expected. I must get my telescope out before summer arrives…