zeller

Zeller is a surname of German origin. It is common in German-speaking regions and among descendants of those communities, and is often connected to topographic or occupational roots related to places named Zell or to historical dwellings. The name appears across various fields through individuals bearing it, including scholars, artists, and professionals.

In mathematics and computer science, Zeller's congruence refers to a family of algorithms for determining the day of the week for any given date in the Julian or Gregorian calendar. The most widely known form, attributed to the German mathematician Christian Zeller, expresses the weekday as a function of the day, month, year, and, when needed, the century. Different variants adjust month numbering and leap-year rules, and several formulations exist to optimize for hand calculation or programmatic use. Zeller's congruence has historical significance in calendrical mathematics and remains a standard example in introductory number theory and algorithm courses.

Beyond the mathematical term, Zeller is encountered as a personal surname in various European populations and appears in toponyms and cultural references in German-speaking regions. The name thus has both onomastic and technical associations, with the congruence representing its most widely cited scientific use.