Explore the cycles of time and the sky
CycleCalcs is a home for the rhythms of the heavens: interactive lessons on how the sky moves, live tools for tonight's sky, fast calculators, and a sorted reference of every major astronomical cycle, from the 29.5-day phases of the Moon to the 25,920-year wobble of Earth's axis.
Right now in the sky
The Moon tonight
Live phase, computed in your browser.
- Coming upmoons & eclipses
Planets in the sky tonight
Explore the sky, live
Interactive, always-current views of the solar system and the night sky, all computed in your browser.
The Live Orrery
Scrub time and watch the real planets orbit, Sun-centered or Earth-centered, from Mercury out to Pluto.
LiveToday in the Sky
Tonight's Moon phase, the planets' places in the zodiac, and the next sky events.
CalendarMoon Phase Calendar
Tonight's Moon and a month grid of the new, quarter and full moons, plus each full moon's traditional name.
EclipsesEclipse Explorer
The next solar and lunar eclipses, their dates and types, and the Saros family each belongs to.
Your locationPlanet Parade Tracker
The next planet parade from your spot, where to look and when, with a live countdown.
GuidesPlanet Conjunctions
When two planets meet in the sky: live dates and how close they pass, pair by pair.
Calculators
Fast, free, and built to show their work, with no signup and running entirely in your browser.
Synodic-Period Calculator
Find the synodic period of two bodies, the average time between their alignments, with the pairwise periods for more.
Planetary Alignment Calculator
Real dates of planetary conjunctions and oppositions, and how often three or more planets line up.
Celestial Return Calculator
Where the Sun, Moon and planets sat on any date, and when each one returns to that spot.
Date Calculator
Add or subtract years, months, weeks and days, or find the exact span between two dates.
Pythagorean Numerology
Add up the classic Pythagorean letter values for words and names, with a total across them all.
All calculators →
Every calculator and sky tool in one place, with more on the way.
Learn how the sky's cycles work
Hands-on, plain-language explainers, each built around a visual you can move and play.
Moon Phases
Why the Moon waxes and wanes over its 29.5-day cycle.
InteractiveEclipses
Why solar and lunar eclipses happen only near the lunar nodes.
InteractiveThe Lunar Nodes
The 18.6-year turning of the Moon's tilted orbit.
InteractiveSun's Declination & Seasons
How Earth's tilt makes the equinoxes and solstices.
InteractivePrecession of the Equinoxes
The 25,920-year wobble that turns the pole star and the zodiac.
BrowseAll Learn topics →
Explore the full, growing Learn section.
Why CycleCalcs
CycleCalcs started as a set of calculators and is growing into a place to understand cycles of every scale, and to make connections between the rhythms of the sky, the calendar, and the patterns people have tracked for millennia. The goal is simple: a site where anyone can come to learn how these cycles work and see them clearly.
- World-class interactive visuals built to make the science click.
- Faithful to the real astronomy, with the method behind every number.
- Free and mobile-first, running in your browser with nothing to install.