Guides
Short answers to the questions this calendar raises, written to be read once.
- The structure of the Persian calendarThe Persian year opens at the vernal equinox, and then twelve months have to fit inside whatever length that year turns out to be. Here is how the months are sized, where the leftover day is kept, and what the era counts from.
- Why printed tables disagreeA printed table gives one start date for a sign and repeats it every year. A computed conversion sometimes gives a different day. The gap is not a mistake in either one — it is what happens when a calendar tied to the sky is written down as a fixed list.
- The forms a single date can takeOne day, several correct spellings. This guide describes what each written form of a date actually is — sortable, numeric, spelled out, dual-calendar — so the choice between them is made on purpose rather than by habit.
- When the Chinese new year fallsThe date moves because the year is counted by the moon and held in place against the sun.