Hebrew Calendar

Explore Hebrew dates, molados, year types, keviyah, dechiyos, calendar cycles and traditional time units alongside astronomy.

Explore monthly Hebrew dates, observances and readings, with Gregorian and Julian dates. Day details connect the calendar to astronomy and configurable halachic times.

Year review shows month lengths, leap years, postponements, molados and tekufos, with the 19-year calendar cycle, 28-year solar cycle and Shemittah cycle. Fixed-calendar projections into early periods are not evidence of the calendar historically observed then.

Separate experimental views compare altered year rules and a continuous calendar according to sighting. The sighting experiment starts from a declared anchor, retains fixed Jewish Day Numbers, and advances months using selected illumination, horizon and sunset-offset criteria. These are configurable research assumptions, not records of witnessed sightings or halachic declarations.

Jewish Cosmology is an interactive research and educational web application connecting Hebrew dates, traditional Jewish calendar calculations and halachic concepts of time with the observable motions of the Sun, Moon and planets, astronomical seasons and eclipses.

JavaScript is required for the interactive explorers and calculations. The descriptions and navigation remain available without JavaScript.