Moon Phases
Why the Moon waxes and wanes over 29.5 days. Switch between a realistic 3-D Moon and a top-down Sun-Earth-Moon diagram.
InteractiveEclipses
Why solar and lunar eclipses happen only when a new or full moon lands near a lunar node, in two synced views.
InteractiveThe Lunar Nodes
The slowly turning points where the Moon's path crosses the Sun's, and the 18.6-year cycle they trace.
InteractiveSun's Declination & Seasons
How Earth's 23.4° tilt swings the Sun's declination over the year, making the equinoxes, solstices and seasons.
InteractiveThe Equation of Time
Why a sundial runs up to a quarter-hour ahead of or behind the clock, and the figure-eight analemma it traces.
InteractivePrecession of the Equinoxes
The 25,920-year wobble of Earth's axis that slowly reshuffles the pole star and the zodiac.
InteractiveApsidal Precession
How the Moon's and the planets' elliptical orbits slowly rotate: the turning of perigee and perihelion.
InteractiveVenus: the 8-Year Pentagram
The morning and evening star, its ~47° dance with the Sun, and the five-petaled rose it draws over eight years.
InteractiveThe Sunspot Cycle
The Sun's 11-year rise and fall in spots, the 22-year magnetic flip, and the butterfly diagram.
How this section works
Every topic is built around something you can move and explore, not just read. The visuals are kept faithful to the real geometry, simplified only where a diagram has to be (distances and sizes are rarely to scale, and we say so). Where a topic has a measurable cycle, it links through to the cycles by length list and the calculators so you can put real numbers to what you have just seen.
This part of the site is growing. Live now: Moon phases, eclipses, the lunar nodes, the seasons, precession, apsidal precession, Venus's 8-year cycle, the sunspot cycle, and the equation of time, with more on the way.