Planetary Alignment Calculator

What this calculates

For the models, accuracy and data behind these figures, see the methodology and sources page.

There are two questions hiding in the phrase "the planets line up," and this tool answers both. The aspect finder takes two or more bodies, an angle, and a date range, and lists every date the bodies reach that angle in our sky. The line-up option takes three or more planets and finds how often they fall close to a single line drawn through the Sun.

Aspects over a date range

An aspect is the angle between two bodies measured along the ecliptic as seen from Earth. A conjunction (0°) is the same direction in the sky and an opposition (180°) is the opposite direction; the presets also include the sextile (60°), square (90°) and trine (120°), and you can type any angle from 0 to 180. Set a From and To date, and the tool scans that span and lists every matching date with its zodiac position. Choose three or more bodies and it checks every pair. Earth has no place in our sky, so for a sky aspect the Sun stands in for it: the Sun opposite a planet is that planet at opposition, and the Sun conjunct or opposite the Moon are the new and full moon.

This is the companion to the Synodic-Period Calculator. A synodic period is the average time between alignments; this calculator gives the actual dates. Every position is computed in your browser from a built-in astronomical model, so no two visitors ever see a stale answer.

Line up through the Sun

For three or more planets, "aligned" here means they lie within about twelve degrees of one line drawn through the Sun. A planet on the far side of the Sun still counts, because it still lies on that line. This through-the-Sun line is the geometrically meaningful one, and it is the sense in which Venus, Earth and Jupiter "line up" about every eleven years. Such a heliocentric alignment is a geometric configuration, not a force: the planets do raise a real combined tide on the Sun, but even when they line up it is only about a millimeter or two high, thousands of times too weak to affect solar activity, the weather, or anything else, so a line-up carries no predictive meaning. It is not the same as a naked-eye "planet parade," where the planets are bunched on one side of the sky at dusk or dawn; that is a separate, viewing-based idea covered by the Planet Parade Tracker.

A truly perfect line-up of many planets effectively never happens, because their orbital periods are not simple multiples of one another. So rather than a single mythical date, the honest answer is how closely a set comes to a line and how often it does so. When a set never even comes close within the search range, the tool says so plainly instead of inventing a number.

Conjunctions and oppositions

A conjunction is the moment two bodies share the same ecliptic longitude in our sky. Paired with the Sun, an inner planet (Mercury or Venus) can be at an inferior conjunction, passing between us and the Sun, or a superior one behind it; an outer planet at opposition to the Sun sits opposite it in the sky and is at its brightest. Each event in the table shows where in the zodiac it falls.

How rare is an alignment

Two planets meet once per synodic period, from a few months to a couple of decades apart. Three planets line up far less often: Venus, Earth and Jupiter manage it about every eleven years, but the spacing wobbles because the orbits are tilted and elliptical. Add more planets, or demand a tighter line, and the rhythm stretches out fast. This is why headlines about "all the planets aligning" are always about a loose gathering in one patch of sky, never a true straight line.

How this tool works

Positions come from the open-source Astronomy Engine running entirely in your browser. For aspects the tool scans your date range and refines each crossing of the target angle to about a minute; for the line-up it finds the moments the chosen planets come closest to a line through the Sun. Zodiac positions are the tropical (of-date) ecliptic longitude, with 0° at the spring equinox. The model is accurate to well under a degree and reliable for roughly the years 1700 to 2200, the limits of the date range.