The type of high-level cloud you're describing is called a cirrostratus cloud.

Here's why:

* High-level: Cirrostratus clouds are found in the high-altitude troposphere, typically above 20,000 feet.

* Thin: They are composed of ice crystals and are very thin, allowing sunlight to pass through them.

* Halo Effect: The ice crystals in cirrostratus clouds refract sunlight, creating a halo effect around the sun or moon.

Let me know if you have any other questions about clouds!