Hollow’s sun is located in the vacuum at the centre of the huge hollow world. The sun is rod shaped – a bit like a fluorescent tube – with its ends pointing about 25 degrees off north and south. It is split in half along its length. One half is bright and shining, the other is dark. As it spins slowly about its long axis it brings its light to bear on half the world at a time. The area directly underneath the light side of the sun receives the full strength of its light and heat while the area on the other side is in darkness.
To an observer who journeys to the far north or south, the sun appears to foreshorten. This means areas receive less and less warmth and light as the observer moves further north or south. At the poles the sun looks more like an elongated dot, either dark or light depending on the season. Underfoot, the poles are solid ice.
Seasons are produced by the tilt of the sun. It takes a day for the sun to spin about its long axis.
It takes a year for the sun to precess, with the tilt leaning from one hemisphere to another thus giving summer to one and winter to the other.
On a clear night the light shining on the opposite side of Hollow bounces back and gently illuminates the night-time landscape. This is called evenshine and is mentioned in Dangerous Ideals. Evenshine is the reflected light from the other side of Hollow much like the way, on Earth, moonlight is sunlight reflected from the moon.