This design is the ancient Celtic calendar which observed four main seasons celebrating transition of the sun through the seasons, time was cyclical, nothing was ever final, everything returned again in a natural cycle.

The outer wheel is the four seasons Samhain, Imbolc, Bealtane, and Lughnassad, along with the Solstice (longest & shortest day) / Equinox (equal day and night), inside this are the Zodiac signs, the inner circle is the Celtic Knot or Triquetra, signifying ‘Life, Death, Re-birth’,  also ‘Mind, Body, Soul’ and ‘Earth, Air and Water’