Friday The moon is set to disappear in the overnight hours between Thursday and Friday, astronomers say. At least most of it will.

A partial lunar eclipse is set to take place from 2:18 a.m. EST to 9:06 a.m. EST — marking the longest astronomical event of its kind in 581 years, according to officials with Chicago’s Adler Planetarium.

It’s expected to reach its maximum eclipse at 4:02 a.m. EST, they say. “At maximum eclipse, almost all of the moon is within the boundaries of the Earth’s darker umbral shadow, leaving only a thin sliver still in the Earth’s lighter penumbral shadow,” reads a statement released by the planetarium.

The spectacle should be visible to sky gazers in North America, Australia, New Zealand, eastern Asia and parts of South America, experts say.