Lunation Calendar · — Deep Dives · — Solar Year

Tilt and the seasons

Earth’s axis stays tilted as Earth travels around the Sun. That changing orientation gives the Sun its annual north-and-south motion in our sky. The solstices are its two declination extremes; the equinoxes are its two crossings of the celestial equator. The solstices produce the year’s longest and shortest days, while day and night are nearly equal in length at the equinoxes. Together, these four events divide the tropical year into seasons.

The same four moments are the Sun’s ingresses into the cardinal signs of the tropical zodiac. That is why a solstice or equinox and a Sun ingress can occupy one Rare Event label, while the Astrological Table adds the symbol for the season beginning there. The other eight Sun ingresses divide each season into thirds without beginning a new one.

Orbit and distance

Earth’s orbit is slightly elliptical. Perihelion is its nearest point to the Sun, and aphelion its farthest. These distance extremes are a different pattern from the seasons: axial tilt, not Earth-Sun distance, is the primary reason the seasons change. Their dates sit near the January and July parts of the year rather than at the solstices.

The Wheel of the Year

The eight Wheel-of-the-Year festivals place a traditional calendar over the same solar cycle. The four quarter festivals align with the solstices and equinoxes; the four cross-quarter festivals fall between them. On the chart, each festival is treated as its own local sunset-to-sunset observance even when it corresponds to the same solar longitude as a seasonal event.