From Keygemin Wiki

The Source is a large sphere in the sky that pulses dark and light about every 29 hours. Places in Una are communicated through a 3 dimensional coordinate system; using the distance from source origin, the radial location in degrees from standard sourceout (north), and elevation over the void cloud layer.

Una has no moving sky objects, no sun, no stars, no moons, no other planets, no galaxies, only the source. A powerful telescope can see descending Gemin, but these kilometer wide gemin are not terribly visible without sourcelight. So at night, they appear black.

This orb is the sole object of illumination in the sky, and thus controls Una's day night cycle. It is a perfect sphere of latent energy, said to be radiating a life giving field. It is so far away that no matter how far you travel across Una, it does not appear to move or parallax in the sky.

Time in Una is kept based on the Source's regular and predictable pattern of pulses. The Source is more regular that any manufactured Chronometer. Timekeeping devices used by the people of Una are commonly gravitational water driven clocks, or spring regulated chronometers. More recently adopted timekeeping devices physically measure the light intensity given off by the Source.