Under the base of the cloud, which is often very dark, there are commonly low ragged clouds that may or may not merge with the base. They are low-level clouds that climb to very high altitudes.

They Are Earth’s Highest Clouds Noctilucent clouds are Earth's highest clouds. They form between Earth and space, about 47–53 miles (76 to 85 kilometers) above the ground in the mesosphere.

Since altocumulus or cirrocumulus clouds often cover a wide area, several of these holes may appear on the horizon, especially in busy flight paths. The clouds also appear quite visibly on satellite.

How weird, and especially so because Enceladus has what's called a high "albedo." That basically means the world is really bright — it's therefore unexpected to find a dark spot on it at all ...

Nimbostratus: Dark gray cloud layer diffused by falling rain or snow. It is thick enough to blot out the sun. Other low, ragged clouds often occur beneath this cloud and sometimes merge with its ...