First page of calendar, with small miniature showing Aquarius, fol. 3

Public domain reproduction of illuminated manuscript page, 14th century, free to use, no copyright restrictions image - Picryl description.

A book of hours is a type of devotional text that was popular in the Middle Ages, particularly in the late medieval period. It is a type of prayer book that contains a collection of prayers and devotional texts that were meant to be read at specific times of the day, known as the "hours." These texts were usually written in Latin and were intended for personal use by laypeople, although some were also used by monks and other religious figures. The book of hours typically included a calendar of feast days, psalms, and other prayers, as well as illustrations and decorations.