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29 September 2026 2518 stories tracked

Glossary · The Solar System

Synodic period

How long until two moving bodies return to the same alignment — the number mission planners live by.

The synodic period is the interval between successive identical alignments as seen from a moving observer, rather than against the fixed stars. Mars orbits in 687 days but returns to opposition every 780, because Earth has moved too. That 26-month rhythm is why Mars launches come in clusters, why rovers arrive in batches, and why a missed window is a two-year delay. The Moon's synodic month, 29.5 days, is the one everybody already knows: new moon to new moon.

Related terms

Gravity assist Stealing a fraction of a planet's orbital momentum to go faster for free. Regolith The layer of broken rock and dust covering an airless world — and a serious engineering problem. Sample return Bringing a piece of somewhere else back to a laboratory on Earth. Opposition and conjunction The two alignments that decide when a planet is worth looking at and when it is unreachable.

Questions

What is Synodic period?

How long until two moving bodies return to the same alignment — the number mission planners live by.

Why does it matter?

That 26-month rhythm is why Mars launches come in clusters, why rovers arrive in batches, and why a missed window is a two-year delay. The Moon's synodic month, 29.5 days, is the one everybody already knows: new moon to new moon.

Written and computed by . Corrections and errors to hello@cantinalabs.dev.