Abydion, the Fifth City
In the time of the Fifth City, all that remains of Earth is a continent-sized rock orbiting a distant, bloated red sun. The rest of the planet was deliberately destroyed in AM 5550 to propel this fragment out to a safe distance, where it would not be engulfed by its swelling star.
The new orbit of Earth trails behind Saturn, which is visible in the sky at all times, day and night. Both the sun and Saturn vary in apparent size from time to time for reasons which modern scholars are not able to satisfactorily explain.
The arts used to destroy the planet have also preserved some semblance of its original natural environment, although the divisions of time are much more consistent than in the 21st century. The day remains 24 hours, but is divided into 15 hours of daylight and 9 hours of darkness. Seasons continue to progress, each lasting approximately 90 days, for a 360-day year, despite the actual orbital period around the sun being much longer. Temperatures average 20 to 25C in the summer and -5 to -10C in the winter. According to the scholars of Arevar College, this climate is consistent across the entire remains of Earth.
A functioning ecology was also maintained, despite reported observations of the seas falling off the edge of the world. (Note that these reports have never been verified by any reputable source.) Several natural animals known in the 21st century remain, but they have also been joined by a host of other creatures. Only mythology remains to attempt to distinguish which are native to Earth, which were imported by Starwalkers, and which were created by the dark arts of the Skinchangers or False Men.