According to early 16th century literary historian John Bale, he became a Carmelite friar and moved to the university town of Oxford, where he developed a great reputation for his scientific work.
In 1386, at the request of the powerful lord John of Gaunt, he published a Kalendarium of detailed astronomical tables covering the years 1387–1462.
[2][1] Designed for use in the astrologically-based science of the time, the tables were very sophisticated, even including rules for synchronising medical treatment with astronomical cycles, such as the right phases of the moon for blood-letting.
The identification of Nicholas as the Franciscan (Minorite) friar who wrote a text called the Inventio Fortunata, allegedly describing a voyage to Greenland and beyond, was first proposed by Richard Hakluyt, the late 16th-century historian of exploration.
[1][4] Nicholas, however, was a Carmelite, not a Minorite, and if Hakluyt and Dee had read Bale (rather than apparently basing their identification on Chaucer's praise for Nicholas' work with astrolabes), they would have discovered an entry about a Franciscan friar named Hugh of Ireland, who wrote "a certain journey in one volume".