Explore Jewish time through astronomy.
Calendar and Astronomy Glossary
Definitions of molad, sunrise, sunset, tekufot, proportional hours, refraction and solar declination, linked to the tools that use them.
These explanations distinguish astronomical quantities from the calendrical or halachic definitions built on them. Read the calculation settings alongside a result: two tools may agree on the Sun’s position while using different definitions of a time boundary.
Explore related concepts
About Jewish Cosmology
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.
Models, terminology and limitationsHalachic times are unverified, have no rabbinic approval, and must not be relied upon for practical halachic decisions unless and until an appropriate authority approves them.