The first ring of the GaldorCraeft Calendar contains eight concentric rings of the circle of fifths. The circle of fifths is a musical theory tool that helps us understand all 12 notes found in western music and their relationship to each other. I chose to align C major, which has no sharps and no flats, with the summer solstice (the brightest time of the year). F# major is then aligned with the winter solstice (the darkest time of year), and has 6 sharps and 6 flats. At the equinoxes, the time of year where the day and the night are at equal length, is A major and E flat major, which each have 3 sharps and 3 flats. This orientation allows opportunities for creating sound and music that correlates with the turning of the year. It could also be used for playing along with particular times of day, if you imagine the calendar as a clock with noon aligned with the summer solstice.
There are many correlations between music theory and day keeping that can be explored further, but for now it is important to understand that one way musical scales and chords can be described is as sounding relatively darker or lighter. When we move sunwise (or clockwise) around the circle of fifths, from a particular note, the notes get relatively brighter sounding. Whereas when we move counter sunwise, from a particular note, the notes get relatively darker sounding. So, for example, if we take the base note C, all the notes to the right of C, G, D, A, E, B, F# sound bright when played together in a scale or a chord with C as the base note. As we replace these notes with notes from the left side of C, the resulting scales and chords will get relatively darker sounding.
This website was very helpful in understanding the circle of fifths and brightness vs darkness in music.