Skywatchers across the world will witness the first total lunar eclipse in three years. Here’s who will have the best views—and what gives the moon its eerie red tint.

When sunlight hits Earth’s atmosphere during a lunar eclipse, light frequencies toward the blue end of the visible spectrum are scattered outward, away from Earth’s umbra, but those with longer wavelengths, toward the red part of the spectrum, are bent inward and cast onto the moon.