The twinkling effect is caused by the unstable state of the air through which a star's light must pass to reach our eyes. Especially near the ground, the air is almost always turbulent; cold and ...

The stars of the Spring Triangle asterism are shown on a simulated night sky on June 18. Arcturus forms the top of the triangle, with Spica to its lower left.

An unusual atmospheric phenomenon known as a circumhorizontal arc, or "fire rainbow," was spotted in southern Ohio, caused by sunlight refracting through ice crystals in cirrus or cirrostratus clouds.