Astrophotographers 'hate' sky background at night time. This is worst in cities of course with all the street lights, Billboards and what not. We live on the ground and we light up the sky only because we are careless.

Here is a simple data from a series of images i took from my observatory. Starting from 1 sec and doubling the exposure with each image; these are seven in total.

Celestron C14, SBIG ST9XE CCD camera, Astrodon Luminance filter (and more) was used to acquire this data.

Notice a perfect linear relationship here (notice R^2 value). CCD cameras have excellent linear response to star light photons and here, sky background photons. This is the reason we like CCD's or CMOS for that matter (until they remain linear). CCDs are always better than CMOS.. there are many reasons for that.

I have attached a short clip of these seven images as well.. you will see very few stars in a single second exposure and many more with increasing exposure. Telescope was not being guided so you will see black bands in the images; this is the result of aligning unguided exposures.