Monday is the first day of the week, according to the International Organization for Standardization. The name Monday is derived from Old English, literally meaning 'moon's day'. Monday is dedicated to the moon.
The name Tuesday derives from the Old English 'Tiwesdaeg' which literally means 'Tiw's day'. Tiw is the Old English form of the Norse god 'Tyr', the god of war and law. Tuesday is dedicated to Tyr -- Tyr's Day.
The third day of the week is Wednesday, continued from the Middle English Wednesdei which is itself derived from the Old English Wodensday. Woden was a Germanic god similar to the Norse god Odin. Eventually Woden would become the head of the Germanic pantheon. Wednesday is "Woden's Day".
Thursday is the contemporary name for the fourth day of the week which derives from the Old English that is translated as 'Thunor's Day'. In Norse mythology, Thunor is known as Thor, the god of thunder. Thursday is dedicated to Thor, known as Thor's day.
The name Friday comes from an Old English word which means 'day of Frigg', a major goddess in Norse paganism. Frigg, also called Freyja, was associated with love, and is equivocated with the Roman goddess of Love, Venus. As a consequence, in cultures associated with the Roman and Norse pantheons, Friday is considered the day of love and lovemaking.
In parting with the previous traditions, the sixth day of the week, Saturday, is named directly after the Roman god Saturn. The Latin name for Saturday is dies Saturni. Saturday, obviously, is Saturn's day.
Sunday, the seventh day of the week, is derived from the Old English Sunnandaeg, literally translated as 'sun's day', which itself is from the Germanic interpretation of the Latin dies solis, day of the sun.