John Somer (astronomer)

John Somer was a 14th-century English Franciscan friar and astronomer. He is primarily known for his astronomical treatise, Kalendarium, which was completed in 1386.

Kalendarium was a practical guide for calculating the positions of the sun, moon, and planets, as well as determining dates for ecclesiastical feasts and festivals. It was a widely circulated and influential work during the late medieval period, demonstrating a growing interest in accurate astronomical observation and calculation for both religious and practical purposes, such as astrology and agriculture.

Somer dedicated his Kalendarium to Joan of Kent, the Princess of Wales and mother of King Richard II. This dedication likely served to secure patronage and increase the reach of his work within the English court.

While biographical details about John Somer are scarce beyond his authorship of Kalendarium, his work provides valuable insights into the state of astronomical knowledge and practice in late 14th-century England. It represents an effort to synthesize existing astronomical theories with practical applications relevant to the daily lives and religious observances of his contemporaries. The Kalendarium included not only astronomical tables and calculations but also explanations of the underlying astronomical principles. His work is significant for showcasing the accessibility of astronomical knowledge to a wider audience beyond purely academic circles.