An eclipse occurs when one object gets in front of another, eclipsing it in the sky. An eclipse can be total or partial, depending on the alignment of the Sun, Moon and Earth. The shadow cast by an eclipse has two parts: the umbra, or total shadow; and the penumbra, or partial shadow.
When Earth blocks the sunlight that normally reflects off the Moon, the result is a lunar eclipse, which can only occur at full moon.
A total eclipse occurs when the Moon passes into the umbra, or total shadow of Earth. A partial eclipse occurs when the Moon passes through part of the umbra. A penumbral eclipse occurs when the Moon passes only through the penumbra, or partial shadow of Earth.
When the Moon blocks light from the Sun, casting a shadow on the Earth, it's called a solar eclipse. A solar eclipse can only occur at new moon. Solar eclipses occur over a narrow band of the Earth.
The Sun is much larger and farther away than the Moon, but the apparent size of each is sometimes the same (depending on minor changes in distance based on non-circular orbits). When this is the case, a total eclipse can occur. If a thin ring of the sun surrounds the moon, it is called an annular eclipse. In a partial solar eclipse, the moon covers only a portion of the Sun, giving it a crescent shape.
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