In Chinese, the days of the week are numbered. (星期一、星期二、星期三……) In English they have specific names, which makes them more difficult to learn. As proper names they must be capitalised. Worse, very few native speakers even know what the names mean. Sunday and Monday are of course easy to guess. They are the days of the sun and moon. All the others are named after gods.
Usage note: In English the God of a monotheistic religion is capitalised, as a name. When writing about a polytheistic religion (many gods), the creature's name, but not the word god, is capitalised.
Tuesday was Tiw's Day. Tiw is the Old English spelling, the Old Norse spelling was Tyr. He was a son of Woden and the god of war and oaths (promises). He represented authority. Tiw lost one of his hands to the wolf-demon Fenrir.
Fenrir scared the gods. They tried to tie him up, but Fenrir refused. They said that they just wanted to test the rope. He agreed, but only if a god put their hand into his mouth as proof of their good will. Tiw was brave enough to agree. When Fenrir found himself trapped, he bit off Tiw's hand. His one-handed-ness was the symbol of keeping oaths.
Wednesday was the day of Tiw's father, Woden. The Norse spelling was Odin. Woden was the king of the gods. He was god of war, writing, poetry and learning. Reading at that time was a mysterious and magical ability. Woden learned to read runes and gained cosmic knowledge by pulling out one of his eyes. Fortunately no one has done that to learn to read English recently.1
After Woden's day comes Thor's day. The Norse spelling was Thorr. Thor was another son of Woden. He was very popular with farmers and fishermen, because he was the god of weather. His name meant thunder (Old English thunor). So Thursday is the day of the thunder god.
Friday is Frige's day. The Norse spelling was Frigg. She was queen of heaven and goddess of married love. She was famous for her wisdom. She, of course, was the wife of Woden.
Saturday was the day of the Roman-god Saturn. The English naming of the days of the week was copied from Latin. In Latin, the days of the week were named after Roman gods. (dies Solis, dies Lunae, dies Martis etc...) In Old English they used their own gods as substitutions. However these northern gods were violent and warlike. There was no northern god to substitute for the relatively peaceful farming-god Saturn.2 So Saturday remains the day of the farmer's god.
Today most English people do not know the meaning of the day's names, but now you do. This is the names for the days of the week.
1. He gave up an eye to drink from the well of knowledge and was hanged from the world tree Yggdrasil with a spear in his belly to learn the runes. Whether the myth of a god hanging on a tree and wounded with a spear had roots related to Christianity I would not want to venture to guess.
2. The original Christmas was the Saturnalia or festival of Saturn. The festivities were similar to those today. His myths were enriched with some less peaceful ones borrowed from the Greek god Cronus.