By Marie Clay Updated Mar 24, 2022
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Occasionally, the planets in our solar system appear to line up in a row. These configurations can be straight out from the Sun, offset from it, or merely apparent when viewed from Earth. Different types of alignments have distinct names and varying degrees of rarity.
A planetary alignment, or conjunction, occurs when at least two celestial bodies share the same position in the sky as seen from Earth. NASA defines a conjunction as a moment when planets either line up with the Sun or appear in a straight line from Earth's perspective, even if they are on opposite sides of the Sun.
When three bodies—typically the Sun, Earth, and another planet or the Moon—align within the same gravitational system, the configuration is called a syzygy. Syzygy is most commonly associated with eclipses: a solar eclipse happens when the Moon lies between Earth and the Sun, blocking sunlight; a lunar eclipse occurs when Earth sits between the Sun and the Moon, casting its shadow on the Moon.
Partial alignments are relatively frequent; they require only that two bodies occupy the same apparent constellation from Earth's viewpoint. A full alignment with all planets on one side of the Sun is extraordinarily rare—John Savard of Quadibloc estimates it will occur only once every 1.6 million years. A balanced alignment, with planets positioned on both sides of the Sun, can happen roughly every 516 years.
Throughout history, planetary alignments have fueled superstitions and apocalyptic predictions. Recent claims, such as the 2012 Nibiru prophecy, suggested that a hidden planet and a shift in Earth's rotation would trigger global disasters. NASA has debunked these ideas: no such planet exists, Earth's rotation remains stable, and the predicted alignment never materialized.
