A lunar eclipse occurs when the Earth passes directly between the Sun and the Moon, casting the planet's shadow onto the lunar surface. This celestial alignment causes a temporary dimming or obscuring of the Moon, as its reflected sunlight is blocked by the Earth's orbital plane. The depth of the eclipse is categorized based on how deeply the Moon passes through the Earth's shadow, ranging from a partial eclipse, where only a portion of the lunar disk is eclipsed, to a total eclipse, where the entire visible surface enters the darkest part of the shadow, known as the umbra. These events are predictable based on gravitational forces and orbital mechanics, representing a fundamental demonstration of the relationship between the three major bodies in the solar system.