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Solar and lunar eclipses are visible because of the precise alignment of the Sun, Earth, and Moon. The relative sizes of these bodies, their distances from one another, and the near‑coplanar nature of Earth's orbit around the Sun and the Moon's orbit around Earth create the rare conditions needed for these dramatic events.
When the Moon lies between the Sun and Earth, a solar eclipse occurs—only possible during a new Moon. A lunar eclipse happens when the Moon is opposite the Sun (full Moon) and Earth sits between the Sun and Moon. Both types of eclipses are simply different alignments of the same celestial trio.
The Moon’s orbital plane is inclined by about 5° relative to Earth's orbital plane. This small tilt prevents perfect alignments every month, limiting eclipses to a few days each year. If the inclination were zero, we would see at least one solar and one lunar eclipse every month. The tilt has a more pronounced effect on solar eclipses because Earth's shadow is larger than the Moon’s.
A partial eclipse occurs when the alignment is incomplete, allowing some sunlight to pass through. A total eclipse blocks all light from the eclipsed body—Moon darkness during a lunar eclipse, and daytime darkness during a solar eclipse. Observers must use proper eye protection when viewing a solar eclipse.
Because Earth’s and the Moon’s motions are highly regular, both eclipse types are entirely predictable. NASA publishes a detailed schedule of all solar and lunar eclipses through the year 3000, including dates, times, durations, and maps showing where each eclipse will be total, partial, or annular. (Solar eclipses can also be annular when the Moon is farthest from Earth and appears smaller than the Sun.)
For the full NASA eclipse calendar, visit NASA’s Eclipse Website.
