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Cycles · The Cycle Explorer

The cycles that govern the sky.

Everything up there repeats: the Moon's month, the year of the seasons, the 18-year rhythm that makes eclipses return, the slow cone of Earth's axis. This is the reference for all of it - every cycle named and measured, from the 29.53-day lunar month to the 25,920-year turn of Earth's axis.

Find your cycle → Where are we right now? →

The panel below is recomputed by the daily build from the open-source Astronomy Engine; the live board and every calculator here compute in your own browser. Each figure states its convention. How this is computed →

the sky right nowbaked daily

Open the full live board →

Find your cycle

Type a body, a family, or a name. Every cycle in the catalog answers - the flagships open their full reference profile, the rest their catalog entry.

The cycles that carry a full reference profile, in five groups. The catalog slices the whole list more finely, into ten families, mapped on the catalog page.

One reference page per cycle: the stated period and convention first, a live or daily-baked reading of where we are in it now, the math, and the next occurrences computed years ahead.

Lunar months

The Moon keeps several months at once, each measured against a different reference: the phase, the stars, the nodes, the long axis of its orbit.

  1. 27.21 d The draconic monthWhat times every eclipse to the Moon's node crossings?
  2. 27.32 d The sidereal monthHow long does the Moon really take to orbit Earth?
  3. 27.55 d The anomalistic monthWhen is the Moon closest to Earth, and why does its size change?
  4. 29.53 d The synodic monthWhy do the Moon's phases take 29.5 days to repeat?

Eclipse & nodes

Everything here traces back to the Moon's tilted orbit crossing the ecliptic: the node-crossing month, the eclipse seasons, and the long cycles that make eclipses repeat.

  1. 346.62 d The eclipse yearWhy do eclipses come in seasons about twice a year?
  2. 10.9 y The tritosWhat eclipse rhythm returns after 11 years less a month?
  3. 18 y The SarosWhy do eclipses repeat every 18 years and 11 days?
  4. 18.6 y The lunar standstillWhen does the Moon rise and set at its widest extremes?
  5. 18.6 y The lunar nodal cycleWhy do the Moon's nodes slide backward around the sky in 18.6 years?
  6. 19 y The Metonic cycleWhy do full moons fall on the same calendar dates every 19 years?
  7. 28.9 y The inexWhat ties one Saros series to the next?
  8. 54.1 y The exeligmosWhen does an eclipse come back to nearly the same place on Earth?
  9. 76 y The Callippic cycleHow did ancient astronomers hold the Moon to the calendar for 76 years?

Solar & seasonal

The years of Earth's orbit, each measured to a different reference, and the Sun's own activity rhythm from the NOAA record.

  1. 365.24 d The tropical yearWhy is the year of the seasons 365.2422 days long?
  2. 365.26 d The sidereal yearHow long does Earth's orbit really take, measured against the stars?
  3. 365.26 d The anomalistic yearWhen is Earth closest to the Sun, and why does that date drift?
  4. 11 y The sunspot cycleWhere does the 11-year sunspot cycle stand right now?
  5. 22 y The Hale cycleWhy does the Sun's full magnetic cycle take 22 years, not 11?

Planetary

What repeats when planets lap one another, seen from a moving Earth.

  1. 8 y The Venus pentagramWhy does Venus trace a five-petaled rose over eight years?
  2. 19.9 y The great conjunctionHow often do Jupiter and Saturn meet in the sky?

Deep time

The slowest turn on the page: Earth's axis tracing its 25,920-year cone.

  1. 25,920 y Axial precession (the Great Year)Why does the pole star change over thousands of years?

Every other rhythm lives in the catalog by length, each with its period and what it governs.

The cosmic spectrum

Every cycle in the catalog on one logarithmic ruler of time, from a day to a galactic year - eleven powers of ten. Drag to pan, pinch or use the zoom buttons (or Ctrl and scroll) to zoom, and click a cycle to open it.

This interactive timeline needs JavaScript. Every cycle, with its period, is listed in the catalog by length.

One catalog, three lenses

The same cycles, three ways of looking: where they stand now, how they fall across history, and how they interfere.

The reference shelf

The deep surfaces this hub routes into, each with one job.

Spot a cycle that belongs here, or a value worth refining? Write to info@cyclecalcs.com.