There is a center that everything is revolving around, “the axis”. According to certain theories, the further you are from the axis the faster you would be moving. So, if the universe where infinite in space, points sufficiently far from the axis would have to be rotating faster than light (S. Hawking). This would render any object at any such point invisible at its actual location as it will have travelled much further even in a small amount of time. The orbits of the Sky travellers are categorized by the travel height principle: The orbit number will increase with the distance to the observer, i.e. the farther away and the higher above they are.

Summary of orbit categories:
1107. Wondering travellers
1125. Winnowing sky travellers
1125-0,34. Moons
1131. Stationary (state) travellers
1136. Theoretical orbit
1140. Tension-field, force-field, field and satellite
1151. Infinite static universe
1167. Star trekker
Out of orbit: Wandering travellers