The darkest sky with a fisheye lens

I was wanting to try out some night-sky photography with a fisheye lens, but the early evening was very cloudy and not very promising.  However, when I looked outside around 11:30 pm it appeared to be clear.  I assembled an Olympus E-M5iii with a Rokinon 7.5mm f/3.5 fisheye lens and put it on a tracking mount and got set up in the back yard.

The sky was indeed clear, although I could detect some murk along the north and south horizons.  The measured sky brightness directly overhead  was sqml=21.80 mpsas.  I was shocked.  The darkest sky anywhere generally tops out near 22 mpsas, so this is nearly as good as it gets.  I have measured a darker sky here in Creede only once.

Composition with a fisheye lens is tricky.  If the lens is tilted upward, the horizon will curve up on each side as it is in this image:

Rokinon 7.5mm f/3.5, ISO 3200, 60 s.

 This image was processed from the raw data to bring out the faintest details of airglow along the horizon.  The zenith point, where the sky is darkest, is about 1/8 of the frame down from the top.  The sky can never be truly black because of air glow, which is a natural high-altitude phenomenon caused by the sun.  Most of the time it is imperceptible to the eye, but easily picked up by long exposures with a camera.

The constellation Scorpius and its brightest star Antares was just emerging through the murky airglow above Snowshoe Mountain:

 Higher in the sky, a meteor was captured between Corona Borealis and Arcturus: