While people were gazing upward to witness Monday’s spectacular solar eclipse, shadows on the ground were just as fascinating. Some of them even looked like crescents.

According to World Book, in the minute or two before and after the sun is totally blocked, people may notice thin stripes of dark and light shadows moving rapidly, as if in waves.

They are called shadow bands or snake bands. Scientists are unsure what causes it, but it is the same phenomenon that causes stars to twinkle, World Book reported.