This section is from the "The New Student's Reference Work Volume 5: How And Why Stories" by Elinor Atkinson.
Sunday gets its name from the Sun. In olden times many peoples worshiped the sun, the heat and light giver. The sun was believed to be the source of all life. Because they were the most wonderful and mysterious things in Nature, next to the sun, the moon and stars were worshipped as gods of lesser power. The moon was thought to be the wife of the sun, the mother of all things, as the sun was the father. The sun rode his golden chariot by day, the moon her silver chariot by night. He was everything mighty, fierce and strong; she everything gentle, beautiful and good. So the second day of the week was named for the moon goddess—Monday. Tuesday was named for the brave Norse war-god, Tyr, who made the fierce wolf a captive by sacrificing an arm. It is curious that, in French, Tuesday is called Mardi. That comes from the Greek war-god, Mars. The little fiery-red planet Mars is named after the same god. Wednesday was named for Woden or Odin, the chief god of the Norsemen. He ruled over Valhalla, the hall of the heroes slain in battle. That is the reason we keep the "d" in Wednesday. It is really Woden's Day. Thursday was named for Thor, the Norse thunder god. He was the same as the Greek Jove, the strongest of all the gods. Jove and Thor had the cheerful habit of using thunder bolts for hammers. Friday is named for Freya, the wife of Woden and the mother of Thor. You see how fond ancient people were of families of gods. Saturday was named for Saturn, the big planet with bright moon-rings around it. The god Saturn was worshiped by the Romans and he had one special day in the week that was given to feasting and games. This celebration was called the Saturnalia. Perhaps that is why Saturday, today, is more or less of a holiday everywhere. It is as hard to break habits of whole peoples, that are fixed by many generations, as it is for a person to break a habit. You would think it something terrible to have to go to school on Saturday. Hundreds of years ago, in Rome, little boys felt the very same way about it.