Vernal Equinox Day

Vernal Equinox Day, or Shunbun no Hi, is Japan's annual March national holiday to admire nature and love living things. Its Japanese name is Shunbun no Hi, also read Shunbun Bi, but there is no official English name. The Act on National Holidays created it in 1948 as one of the original 9 holidays, and the calendar now holds 16 holidays each year. The Cabinet Office owns the holiday list, while the National Astronomical Observatory of Japan fixes the date by astronomy. It covers all Japan as a single calendar day, and it measures no output, prices, employment, or market volume. It is the Japan Standard Time day holding the equinox instant, not the instant itself, nor September's autumnal date, nor another zone's date.

The observatory computes the sun's crossing of the equinox point continuously, with no field period, sample, or survey. Next year's date becomes official with Reki Yoko, the calendar almanac, in the first Official Gazette each February of the prior year. All Reki Yoko dates use Japan Standard Time at UTC+9h. When February 1 falls on an agency holiday, publication slips to a later gazette day. The same release carries the full holiday table, the 24 solar terms, moon phases, Tokyo sunrise and sunset, and eclipse forecasts. The Cabinet Office posts alongside it its full yearly list holding 16 holidays. Once gazetted, a date is never revised, while multi-decade forecasts stay reference-only on the assumption that Earth's motion holds. The publishers give no market reading, since the law only makes national holidays holidays.

The holiday has no weighted parts, and four determining elements set its single date.

• Apparent ecliptic longitude of the sun: the quantitative driver of the instant, at 0 degrees for spring and 180 degrees for autumn.
• Ecliptic and celestial equator: the sun's path and the sky equator, whose crossings define the spring and autumn points.
• Japan Standard Time calendar-day containment: the holiday is the Japan Standard Time day holding the crossing instant.
• Reki Yoko gazette in February of the prior year: the bulletin turning the computed day into the official holiday.

The March 20, 2025 case shows the shift, since only the February gazette fixes the date. The edition announced on February 1, 2024 listed Shunbun no Hi as March 20, 2025. Its table set the spring crossing at 0 degrees on March 20, 2025 at 18:01. The Japan Standard Time day holding that instant was March 20, 2025, a Thursday. March 21, 2022 and March 21, 2023 came first, then March 20, 2024 and March 20, 2025, so the day never rests on March 21.

1. Holiday definition: the law calls the holiday Shunbun-bi, the equinox day, whose purpose is to admire nature and love living things. The law makes national holidays holidays.
2. Equinox instant: Shunbun is the instant the sun, moving along the ecliptic, crosses the vernal point where the path meets the sky equator.
3. Longitude rule: that instant is when the sun's apparent longitude is 0 degrees, while autumn is 180 degrees and Shunbun is the second Chuu term.
4. Calendar-day conversion: the Shunbun-bi is the Japan Standard Time calendar date holding that instant, so 18:01 on March 20 gives March 20. An instant past local midnight would move the day with it.
5. Formal fixation: the date becomes official only with next year's Reki Yoko in February's first gazette, and the Cabinet Office then lists it. Before that gazette it stands undecided, and long-range forecasts stay reference-only.