'a dark sky' is a correct and usable phrase in written English.
You can use it to describe a physical feature of a setting, for example: "The sun had set and a dark sky had blanketed the town."
A dark sky beyond Coney Island's contorted steel skyline.
A dark sky and a telescope or a good pair of binoculars should reveal it.
"There is really nowhere you can go to really see a dark sky," he said.
A brightly lit face against a dark sky -- a modern western".
You need a headlamp to get around at night, biking on unpaved trails under a dark sky spackled with stars.
On the slope above, silhouetted on a dark sky, a wall of white descended toward our perch.
The ship is set against a dark sky and not distorted by the artificial light you find in cities.
"The country was a ship afloat with no compass and a dark sky," says Mohsen al-Awaji, a cleric and former government critic.
He and his playing competitors Mickelson and Harris English had a dark sky behind them but a clear path in front of them.
And it wears a bit of show-car bling: a grille with gleaming metallic points supported by almost invisible black stems — like stars in a dark sky.
"I came here in 2008 because my husband died and I had to bring up three children," said Abigail Dza Dza, as a dark sky overhead threatened rain.
