Zoroastrian Roz-o-Mah (瑣羅亞斯德曆)

The Day-Yazata — Reading a Date in the Ancient Persian Calendar

Overview

Long before the modern week, the Zoroastrians of ancient Iran kept a calendar in which every single day had a name and a divine guardian. Their year ran twelve months (Mah) of thirty days each, plus five sacred 'Gatha' days to complete the 365 — and each of the thirty days (Roz) was named for and watched over by a Yazata, a divine being or 'one worthy of worship': the first day belongs to Hormazd (Ahura Mazda, the Wise Lord) himself, the sixteenth to Mihr (Mithra, lord of the covenant), the twentieth to Bahram (Verethragna, victory), the thirtieth to Aneran, the endless light. To know a day in this calendar is therefore to know which divinity colours it. The most beautiful feature is the NAME-FEAST, or Jashan: whenever the name of the day matches the name of the month — the day of Tir falling in the month of Tir, the day of Mihr in the month of Mihr — that coincidence is celebrated as a festival, giving Persia its great feasts of Tiragan and Mihragan. askTIAN converts any ordinary date into this calendar with exact astronomy, reads the day through its Yazata, surfaces every feast, Gahanbar and watch that falls on it, and is candid throughout that this is Zoroastrian religious-cultural heritage for reflection — never prediction.

Origin & history

The Zoroastrian calendar is one of the oldest continuously-meaningful calendars on Earth, the liturgical reckoning of the faith Zarathushtra founded in the Iranian world more than two and a half millennia ago. Its thirty day-names and twelve month-names are drawn directly from the Avesta — specifically the Sīh-rōzag ('the thirty days'), a litany that dedicates each day of the month to its presiding divinity, the seven great Amesha Spentas (Bounteous Immortals) and the host of lesser Yazatas. The structure — twelve thirty-day months and five epagomenal days named for the five Gathas, the hymns of Zarathushtra himself — was standardised under the Achaemenids and refined under the Sasanians around the fifth century CE. After the Islamic conquest the tradition survived among the Zoroastrians of Iran and, most enduringly, among the Parsis who migrated to India; their priests have kept the day-count unbroken to the present, and the great festivals — Nowruz at the spring equinox, Mihragan in autumn, Sadeh in deep winter — are still observed by communities from Yazd to Mumbai.

askTIAN is precise about what is firm and what varies. The thirty Roz names, the twelve Mah names, the five Gatha days, and the Amesha Spentas and Yazatas who govern them are drawn from the Sīh-rōzag and cross-checked across the Avestan scholarship, Wikipedia, the Heritage Institute and the Encyclopaedia Iranica with no conflicts in their order — the three 'Creator' days at positions 8, 15 and 23 (all dedicated to Ahura Mazda) and the anchors Mihr=16, Aneran=30 are unanimous. The name-feasts are derived honestly from the shared identity of the day- and month-Yazata, which reproduces the attested set of fifteen (eleven to individual Yazatas plus the four Creator/Daygan days). Where the tradition genuinely diverges, askTIAN says so: the exact day-boundaries of the six Gahanbar seasonal feasts vary slightly between community calendars (the avesta.org values are used); the festival of Sadeh has a mainstream Kermani date and a different Yazdi one; and — most importantly — three calendar variants are in living use. The FASLI (seasonal) reckoning keeps Nowruz on the vernal equinox by intercalation; the SHAHANSHAHI of the Parsis and the KADMI of the Iranian orthodox are 365-day 'vague' years that have drifted by months, with Kadmi running exactly thirty days ahead of Shahanshahi. Critically, the per-day auspice notes are an honest reconstruction from each Yazata's attested domain — not quotations from a classical day-omen text — and no day is ever marked unlucky.

How it works

Everything follows from the date by deterministic calendar math, with one genuine piece of astronomy. askTIAN converts the Gregorian date to a Julian Day Number, then finds that civil year's Nowruz: in the FASLI variant Nowruz is the day of the vernal equinox, which the engine computes by Newton-iterating the project's own tropical Sun ephemeris to longitude 0° (no new dependency) and taking the civil date in Iran Standard Time — this reproduces the official gold vectors, with Nowruz on 2024-03-20 and 2025-03-20 and always falling on 19–21 March across 2000–2050. The number of days since Nowruz then fixes the position in the year: days 1–360 give the Roz (day-of-month 1–30) and Mah (month 1–12), days 361–365 the five Gatha days, with a sixth intercalary day appearing in a Fasli leap year. From the Roz the engine names the presiding Yazata and its attested domain; from the coincidence of Roz-Yazata and Mah-Yazata it flags any name-feast (Tiragan at Roz Tir / Mah Tir, day-of-year 103; Mihragan at Roz Mihr / Mah Mihr, day-of-year 196). It also detects the six Gahanbar seasonal feasts, the Muktad across the Gatha days, and Sadeh; and, given a clock time, the five Gah watches of the day (Havan, Rapithwin, Uzerin, Aiwisruthrem, Ushahin), honouring the attested winter suspension of Rapithwin into 'Second Havan'. The Shahanshahi and Kadmi variants are computed in parallel from their confirmed 2000 epochs (anchored so Kadmi stays exactly thirty days ahead of Shahanshahi) and reported alongside. The response is structured throughout, with an optional best-effort LLM reading in five parsable sections and explicit honesty rails.

Good for

Use cases

Day-Yazata Reading

Send a date and get the Roz with its presiding Yazata and domain, the Mah and its Yazata, the day-of-year, and a domain-grounded auspice — a deterministic spine for a 'what does this day mean in the Zoroastrian calendar' feature, no LLM required.

Feast Calendar

The response flags every observance on the date: the name-feasts (Tiragan, Mihragan…), the six Gahanbar, the Muktad days, Nowruz and Sadeh — ideal for a Persian cultural-calendar or festival-reminder product anchored on real calendar arithmetic.

The Gah Watches

Supply a clock time and the engine returns the Gah (one of the five watches — Havan, Rapithwin, Uzerin, Aiwisruthrem, Ushahin) with its theme, correctly switching Rapithwin to 'Second Havan' in the winter months as the tradition prescribes.

Variant Comparison

Because the engine computes the Fasli, Shahanshahi and Kadmi reckonings in parallel, an app can show all three day-names for the same date and explain why they differ — Fasli pinned to the equinox, the two vague years drifted apart by exactly thirty days.

Key terms

Roz
A day of the Zoroastrian month, each named for and presided over by a Yazata. The thirty run Hormazd, Bahman, Ardibehesht … Mihr (16) … Aneran (30), with Ahura Mazda the Creator honoured on days 1, 8, 15 and 23.
Mah
A month of the Zoroastrian year, also named for a divinity — Frawardin (the Fravashis), Tir (Tishtrya), Mihr (Mithra), Aban (the Waters), Adar (Fire), Day (the Creator), and so on through the twelve.
Yazata
A 'being worthy of worship' — a divinity of the Zoroastrian pantheon, including the seven great Amesha Spentas (Bounteous Immortals) and many lesser Yazatas, each governing a domain of creation or virtue and presiding over its day and month.
Jashan (name-feast)
A festival arising when the name of the day equals the name of the month — the day of Mihr in the month of Mihr gives Mihragan, the day of Tir in the month of Tir gives Tiragan. The tradition attests fifteen such days, eleven to individual Yazatas and four to the Creator.
Gatha days
The five epagomenal days added after the twelfth month to complete the 365-day year, each named for one of the five Gathas (hymns) of Zarathushtra — Ahunavaiti, Ushtavaiti, Spentamainyu, Vohuxshathra, Vahishtoishti — and observed as the Muktad, when the souls of the dead are remembered.
Gahanbar
The six seasonal feasts of obligation, each honouring one of the primordial creations in order (sky, water, earth, plants, animals, mankind): Maidyozarem, Maidyoshahem, Paitishahem, Ayathrem, Maidyarem and Hamaspathmaidyem.
Gah
One of the five watches into which the Zoroastrian day is divided for prayer — Havan (sunrise to noon), Rapithwin (noon to mid-afternoon), Uzerin (to sunset), Aiwisruthrem (to midnight) and Ushahin (to dawn). In winter Rapithwin is suspended and prayed as Second Havan.
Fasli / Shahanshahi / Kadmi
The three living variants of the calendar. Fasli (seasonal) keeps Nowruz on the vernal equinox by intercalation; Shahanshahi (the Parsi reckoning) and Kadmi (the Iranian orthodox) are 365-day 'vague' years that have drifted from the seasons, with Kadmi running exactly thirty days ahead of Shahanshahi.

API

The askTIAN Zoroastrian Roz-o-Mah API converts any Gregorian date to the ancient Persian/Avestan calendar and reads the day through its presiding Yazata. The year is twelve months (Mah) of thirty days (Roz) plus five Gatha days = 365; each Roz and Mah is named for a divinity from the Sīh-rōzag. From one date the engine returns the primary calendar date (the Roz with its Yazata and attested domain, the Mah with its Yazata, the day-of-year), all three living variants (Fasli, Shahanshahi, Kadmi), this year's Fasli Nowruz, every feast or observance on the day — the name-feasts (Tiragan, Mihragan, Abanagan, Adargan, Bahmanagan, Esfandgan and the Daygan days), the six Gahanbar, the Muktad/Fravardigan, and Sadeh — and, given a clock time, the Gah watch with the winter Rapithwin → Second Havan rule. Accuracy is the priority: the Fasli Nowruz is pinned to the vernal equinox by Newton-iterating the project Sun ephemeris (locked by unit test to the official 2024 & 2025 dates of 20 March, and to Nowruz always falling 19–21 March across 2000–2050), and the feast coincidences are locked to their day-of-year (Tiragan 103, Mihragan 196). It is honest about its sources: the Roz/Mah names and Yazata domains are from the Sīh-rōzag and cross-checked with no order conflicts; per-day auspices are an honest reconstruction from each Yazata's domain, not quotations from a classical day-omen text; no day is ever marked unlucky; Gahanbar boundaries and the Sadeh date vary by community and are documented; and the three variants share identical roz/mah arithmetic, differing only in epoch. The whole reading is symbolic Zoroastrian religious-cultural heritage for reflection, not prediction — and not medical, legal, or financial advice. A best-effort LLM reading is returned in five parsable sections; set interpretation:false for structured data only.

Endpoint: POST /trpc/zoroastrian.rozOMah — 6 TIAN Points. See the API documentation and Playground.