The Badí (wonderful) calendar is flawlessly solar, more so than the widely used Gregorian calendar. It synchronizes to the earth's position relative to the sun each year at the March equinox. The calendar sets the rhythm of the Bahá’í community.
The calendar has 19 months of 19 days. A Feast is held on the first day of each month. Each month has an Arabic name for some attribute of God. Arabic words generally have multiple meanings. An attempt is made, below, to convey the additional meanings, all of which can be considered together. To fill the entire solar year, intercalary days (like leap days) are added and given its own name. The days of the month follow the same cycle as the 19 months of the year. The years are also named and follow their own cycles. Although interesting, they are not yet in common use. You can learn more about those and additional details about the calendar in a YouTube video on the subject in Resources.
Riḍván is a twelve day festival celebrating the Declaration of Bahá'u'lláh, three days of which are designated as Holy Days. Two Holy Days float: Birth of the Báb is observed on the first day after the eighth new moon after Naw-Rúz and Birth of Bahá'u'lláh on the next day. Naw-Rúz is set at the vernal equinox occurrence relative to sunset in Tehran, usually March 21st, often 20th, rarely 19th or 22nd. The calendar is flawlessly solar, adjusting annually using 4 or 5 intercalary Days of Há per year. Bahá'í day begins at sunset. Work is suspended on all Holy Days except for the two indicated. Observance time is based on standard local time, hence events are held one hour later if daylight savings time is in effect.