Uposatha days

The Uposatha is a special day for intensified practice — the 14th, 15th and 8th lunar day of each half-month. A list of the key suttas, from which you can work out for yourself when and how to keep the Uposatha, is here.

The calendar shows the Uposatha days as the suttas describe them. Below is the real page, a live demo.

Open in a new window

Where it works

• iPhone and iPad — Uposatha by the Suttas on the App Store: the calendar as an app, with reminders and widgets for the home screen and the lock screen.
• Android — Uposatha by the Suttas on Google Play: the calendar as an app, with reminders and home-screen widgets; a long press on its icon shows the next Uposatha days.
• Windows 11 — Uposatha by the Suttas in the Microsoft Store: the calendar in its own window and three widgets for the Widgets Board (Win + W, then "+"). Uposatha + kala — how long to the next Uposatha day and whether it is the time for food now; Day & night — the part of the day or night that is going on; Month — the month with the Uposatha days marked.
• Telegram — /uposatha in the chat of @dgift_bot, or @dgift_bot uposatha Chiang Mai typed in any chat: the next 30 days with the sun times of your city. More on the Telegram bot page.
• Any browser — the calendar page; the browser's menu installs it as a web app (the "Web App" badge at the bottom of the page does the same where the browser allows it).

Reading the calendar

Five tabs (at the top on a wide screen, at the bottom on a phone). Summary gives the Moon now — its phase, the lit part and the lunar day — with a countdown to the next Uposatha, the Meals card and "From the suttas", passages on the Uposatha ("Show all" lists them). Uposathas has two views: "By dates", a table with the beginning and the end of each Uposatha and the Moon, and "Uposatha days", a list by months and weeks. Calendar is an ordinary month with the days marked; tap a date for its details. Night–day is the structure of the night and day (below), and Suttas the key suttas, each opening at the passage.

Dates. A day in the suttas begins in the evening ("night and day", AN 3.70), so an Uposatha is dated by the evening it begins and lasts through the night and the next day. In the month calendar the evening date has a ring; the next date, the day of that Uposatha, has a dashed ring. When the 14th and the 15th follow each other, the three dates read 14 · 14–15 · 15: on the middle one the 14th is still going in the day and the 15th begins in the evening. The 15th is filled; the 8th and the 14th are rings.

The lines of a date. Begins — the evening; Ends — the next evening; Lunar day — the real lunar day of that Uposatha, for checking (with "Details" on, also its age and when it ends). Real lunar days are numbered 1 to 30 through the month (the Moon gains 12° on the Sun each day); the suttas name the days by their number within a half, so the 8th day of the waning half is the 23rd of the month and the 14th of the waning half the 29th. A lunar day changes at an exact moment, not at midnight, and lasts 19 to 26 hours, so against the calendar dates a number sometimes appears twice or is skipped; the calendar reads this from the real Moon and says so in a note under the date. The lunar day is read at the dawn that follows the evening, because the daytime of the Uposatha lies there.

The full and the new moon are moments and often fall on the next date; they are marked on the date they really fall on, with the time.

Dates can differ by a day. The moments come from an astronomical model, accurate to about a minute. Thai, Sri Lankan and Burmese communities calculate their calendars by tradition and can differ from these dates by a day; if you keep the Uposatha with a particular community, follow its calendar.

Settings

Open the settings (the gear ⚙ at the top). They are in folding groups — "General settings" (language, theme, font size), "Uposatha settings", "Meals" and "Parts of the night and day"; what you leave open is remembered. The link "change" on the Summary tab and "set a place" on the Night–day tab lead straight to the place.

Time zone and hemisphere (under "Advanced"). The moments are shown in your time zone; the hemisphere decides which side of the Moon is lit in the pictures. When a place is set, both are taken from it and the manual fields are hidden.

Place. With your location (or a city typed in the field) the evening is the real sunset and the sun's times are shown; without it the evening is taken at 18:00 and the day parts at 06:00 – 18:00, marked with an asterisk. The location is used only in your browser, rounded to about a kilometre, and is not sent anywhere. "Update my place automatically on opening" finds it again once a day, so the times follow you when you travel.

Week starts on. Monday or Sunday; until you choose, Monday in Russian and Sunday in English.

By the suttas. On — the Uposatha as in the suttas, six days a month, counted from the evening. Off — the modern scheme: four days a month, the dates of the new moon, the first quarter, the full moon and the last quarter (the label turns burgundy so that it is not mistaken).

Details. Off — every date in one short line.

Moon of every day in the calendar. On — the Calendar tab draws the Moon in every date, not only on the Uposatha days.

Twilight. "Dawn and dusk" lets you count the day from sunrise and sunset, or from civil, nautical or astronomical twilight. It needs a place.

Reminders. "Remind in advance" — choose when, from "when it begins" up to two days before; "Remind on the Uposatha day" — at the time you set (06:00 by default). Then the sound and the days: by default the 8th and the 14th; the 15th can be added. The reminder for the 14th says that there are two Uposatha days, the 14th and the 15th. On the site a reminder comes only while the page is open or running in the background of your device (the sound you choose plays then too); Safari and iPhone can hold it back. In the apps for Android and iPhone the reminders are set on the device itself and arrive with the app closed, each with its own sound. Or add the days to your phone's calendar.

Your own calendar (on the site; in the apps the reminders are the device's own). The button "Add to calendar" (and the same row in the settings) opens the options:

• Apple opens the subscription in Apple Calendar (also other apps that accept a webcal link); Google opens the "add by URL" form in Google Calendar; Copy link gives the link for any other program. A subscription (the /uposatha.ics feed) covers the coming year and renews itself. Nothing is stored on our side — the link carries your choices (place, scheme, reminder time), so the same link gives the same calendar to whoever opens it. Apple Calendar keeps the alarms from the feed; Google Calendar ignores them for subscribed calendars and uses its own default notifications.
• Download .ics file adds the next 12 months once, with alarms, to any calendar. It does not update afterwards.

Share copies the link to the page or opens the share sheet of your device.

Meals

The card "Meals" shows the time for food (dawn to midday) or vikāla, "the wrong time" (midday to the next dawn; Pc 37). Midday is counted by the sun, the middle of the day, or the clock. The bell in the corner of the card switches on reminders for the end (default sound: the Vinaya definition of vikāla, read aloud) and for the beginning of the time for food; in the settings they can come on Uposatha days or every day.

Structure of the night and day

The suttas divide the day into three parts — pubbaṇhasamaya (morning), majjhanhikasamaya (midday) and sāyanhasamaya (evening) — and the night into three parts — paṭhama yāma, majjhima yāma and pacchima yāma (MN 53; AN 8.9; Ud 1.1). The page cuts the time from sunrise to sunset into three equal parts, and from sunset to sunrise likewise, for your place and today's date, and marks the part that is going on now. This is conventional, for illustration: the suttas give no clock times, and the parts are longer or shorter with the season.

What is written by each part — alms in the morning, seclusion at midday, meeting in the evening; walking and sitting, the lion's posture, rising — is how the arahants and other monks of the suttas spend it (SN 28.1, MN 53): a picture from the suttas, not a rule; a layperson is not required to do so. The word majjhanhikasamaya itself is in MN 79 ("the sun at midday"); SN 28.1 does not use it, but describes that part of the day: after the meal, the day's meditation, coming out in the evening.

Reminders of the parts. The bell by the heading sets a reminder at the start of each part: by default only the day parts, on Uposatha days, with the part's name read aloud in Pali. The night parts, every day and the sound are in the menu.

Other moon tools

The beginning and the end of a lunar day and the phases of the Moon are astronomical data. To check them or to see them another way:

• Website: Time and Date: Moon Phases
• Apps: Daff Moon Phase (Android) or MOON (iOS)
• For developers: lunarphase-js; this calendar itself uses astronomy-engine.