Radole
A world tidally locked to its star, a "ribbon world" inhabited by merchant spacers known as "Traders" during the era of Foundation and Empire. Its houses and gardens were built to face the motionless "morning sun", while a short distance away there was everlasting night; Asimov wrote this at a time when Mercury was assumed to turn one face always to the Sun.
Read more about this topic: List Of Foundation Universe Planets