Myrion has a single moon. It is named Hiropion by astrologers, but everyone simply calls it “the moon”. It figures prominently in many religious and cultural traditions.
According to modern astronomical understanding, the moon is a spherical body with a radius of precisely 1/3 Myrion’s radius, which completes a single orbit of Myrion every 30 days exactly. Over the course of these 30 days, it undergoes a series of phases depending on which part of the moon is lit: three nights of new moon (dark), twelve nights of waxing (getting more light from right side each night), three nights of full moon (completely lit), and twelve nights of waning (getting darker from right side each night). The Orthonic Calendar is lunar-based: the night of the first day of each month is always the middle night of new moon.
The moon’s rotation is a bit out of sync with its revolution, meaning that the moon is seen at a slightly different angle at each full moon. It takes 20 years for the moon to complete a full rotation (relative to Myrion). The rotational positions of the moon relative to Myrion are called aspects, and they play an important role in lunar astrology (see below).
Powerful spellcasters can cast magic to teleport themselves to the moon. Their writings say that it is cold, with a thin atmosphere. It has hills, mountains, ridges, valleys, craters, and at least one sea of ice. There are a few scrublike plants, but no animal life that the travelers could find.
The moon figures centrally in various religious and cultural traditions. It is understood to be a powerful nexus of spiritual power, and possibly a gateway to another plane.
Hiropeh is the goddess of the moon in Celestialism. The moon is the eye of Hiropeh, shining down on anyone who would use the darkness as a cover for their wickedness. Hiropean clerics feel stronger connections to their goddess or enhanced powers during nights of the full moon, and some experience mystical visions during the new moon.
Onsha, goddess of the ocean, is also connected with the moon. It is taught that Hiropeh formed the moon out of ice from the ocean depths. The ocean and the ice at the core of the moon are still mystically connected, and this phenomenon is what creates the tidal effect by which the world’s oceans “bulge” out towards the moon.
The moon rotates slowly with respect to its orbit around Myrion. To a viewer on the planet, the moon appears to complete one rotation every 20 years. The ancient Idoyans recognized various shapes and figures in the light and dark patches on the surface of the moon. They called them aspects. The Idoyans derived a lunar horoscope system based on which of these aspects was closest to the apparent center of the moon each year. The same system is in use throughout much of the world today, including Orthon and Tornon.
It is possible to determine the current aspect by dividing the current year by 20 and comparing the remainder to the following chart. (Treat 0 as 20.)