Oberon is a small, spherical planet that is physically very similar to Earth which makes it quite unusual in a cosmological sense.
Oberon, as a planet is approximately the same size as Earth. From poles to the equator, Oberon is about 11000 miles (17700 km).
Position in the Universe
Most learned scientists agree that Oberon is at (or very close to) the centre of it's local planetary system, if not the centre of the Universe itself. The sun and moon orbit Oberon on a regular and predictable pattern. There are arguments that the stars themselves also slowly orbit Oberon although those who believe the stars to have special religious significance dispute these findings.
Oberon has gravity. This is lucky as otherwise many objects would be thrown off the ground and it would make farming difficult. The acceleration due to gravity on Oberon has never been precisely measured but it appears to be about the same as that of Earth.
As far as the inhabitants of Oberon are concerned, light travels very, very fast (much faster than, say, an arrow). In a very real sense, light travels 'at the speed of light'. However, unlike in our reality, the speed of light is not entirely constant and can be altered by very powerful magics.
Oberon has one moon, called Puck.
In the night sky Puck looks much the same as our own Moon except that it is considerably larger in the night sky. If you hold a 6cm disk out at arm’s length, that’s the size of Puck in the night sky.
It is the phases and position of Puck that regulate the Imperial calendar. Puck also appears to have an effect on the tides, although there is debate amongst Oberon's scientists as to how strong this interaction is.
Oberon gets its daylight from its Sun which, as everyone knows, is very hot and very bright. Its distance from Oberon has never been accurately measured but as flight and teleportation are both possible on Oberon most people know that it isn't 'close'. Estimates from a few tens to many thousands of kilometres have been calculated but the topic is much in dispute. As the Sun is 'very far away' but is still visible it can also be assumed to be 'very big' but again just how big is not a simple thing to work out.
It is the movement of this sun that determines the years on Oberon, which are of a similar length to our own years.