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Writing on Kiddush Hachodesh — the astronomy and mathematics of the Jewish calendar — and related subjects.

Interactive

Two skies, one motion

An orrery that moves between the sun-centred sky, the earth-centred sky, and the Rambam's nine nested galgalim — with the sun and moon driven by the Rambam's own figures from Hilchot Kiddush HaChodesh.

Text & translation

Hilchot Kiddush HaChodesh

The Rambam's laws of the new month in Hebrew with a new English translation alongside, chapter by chapter.