New Moon Day

Each day runs from sunset to sunset. This site lists every feast and month by the evening it begins: a feast shown as Mon, Sep 21 begins at sunset that Monday and ends at sunset on Tuesday. A seven-day feast shown as Sat, Sep 26 – Sat, Oct 3 begins at sunset on Sep 26 and ends at sunset on Oct 3.

Passover is the one exception in wording: it falls “at twilight” at the end of the 14th (Lev. 23:5), so its date is that evening — the same evening Unleavened Bread begins.

When the new crescent is seen from the land of Israel, the site’s administrator records the evening it was seen — and, where known, who saw it, where and at what time. That report is shown under Last sighting.

A reported sighting always takes priority over the prediction: it fixes the start of its month, and every later month, feast and estimate is counted from it. Reports apply to Israel only; for any other location the site shows the astronomical prediction.

The administrator also records evenings when the crescent was looked for and not seen. Not seeing it on the evening that ends day 29 settles the month at 30 days, so the next month begins the following evening.

The Moon’s cycle averages 29.53 days, so a month that begins with a sighting is never shorter than 29 days or longer than 30. After a month begins, the next crescent is looked for on the evening that ends day 29:

• If it is seen, the new month begins that evening.
• If it is not seen — because of clouds or because it is still too early — the month is complete at 30 days and the new month begins the next evening.

When no sighting has been reported for a month, the site does not assume 30 days. It estimates the next possible sighting — the evening of day 29 if the crescent should be visible to the naked eye then (zone A or B), otherwise day 30 — and marks that month estimated until a report comes in.

“Day 29” counts days of the month since the crescent was seen. It is not the Moon’s age since the conjunction, which the crescent pictures under What the crescent looks like use.

The Overview and Calendar count from the last reported sighting with the 29/30-day rule. The Data tab also lists the purely astronomical prediction — the first evenings after the conjunction on which the crescent could be seen — as its own columns in the Crescent Evenings table, and in Conjunctions & First Visibility.

They usually agree. They differ when a crescent was seen a day earlier or later than predicted (weather, a borderline evening), because every month after that is counted from the actual sighting.

Month 1, Aviv, is the Head of the Year (Exod. 12:2). It begins with the new moon once the barley in Israel is aviv — in the ear and ripening (Exod. 9:31; Deut. 16:1).

At the end of month 12 the latest barley report, from months 11–12 up to the evening of the new moon, decides:

• Aviv found → that new moon begins month 1.
• Not yet aviv → a 13th month is added, and month 1 follows it.

With no barley report yet — and for every future year — the site estimates: the new moon begins month 1 if its 14th day (Passover) falls on or after the spring equinox, otherwise month 13. That is why the Data tab lists the spring equinox.

Other months count on from the most recent numbered month. The administrator can also set a month number on a sighting, which overrides the count.

Head of the Year · 1/1

The evening month 1 begins (Exod. 12:2).

Passover · 1/14

At twilight at the end of the 14th (Lev. 23:5).

Unleavened Bread · 1/15–21

Seven days (Lev. 23:6–8).

First Fruits

The day after the weekly Sabbath during Unleavened Bread — always the Sunday within those seven days (Lev. 23:10–11).

Feast of Weeks (Shavuot)

Count seven Sabbaths and the day after: the 50th day, counting First Fruits as day 1. It always falls on a Sunday (Lev. 23:15–21).

Day of Trumpets · 7/1

Lev. 23:24–25.

Day of Atonement · 7/10

Lev. 23:27–32.

Tabernacles · 7/15–21

Seven days (Lev. 23:34–36).

The Eighth Day · 7/22

Lev. 23:36, 39.

The Calendar shows one year at a time: this year’s spring feasts until Shavuot is over, and this year’s fall feasts until the Eighth Day is over. Only then do next year’s feasts appear. Next year’s fall feasts wait until its month 1 is decided — month 1 has begun, aviv barley was found, month 1 was set on a sighting, or a 13th month has begun.

Overview

The Moon now, the next crescent watch (where and when to look, its zone and the weather) and the next few events.

Calendar

Months with their feasts, dated by the evening each begins, with the crescent watch that decides each month.

Data

Every number behind the page, as tables with units: the crescent evenings (Odeh parameters and weather), the month chain, conjunctions, equinox and method. Also available as JSON through the API.

est.

An estimated month: no sighting has been reported for it yet, so its start (and its feasts) can still move.

now

A feast that is under way.

A … D

Odeh visibility zones — see What the visibility zones mean.

Everything here is available as JSON through a free API: the Moon now, the crescent evenings with their visibility zones and weather, and the calendar with its feast dates. It needs no key and can be called from any website or script.

Read the API documentation ›

The Moon passes through its phases over about 29.5 days:

The new crescent grows each evening after the conjunction (the astronomical new moon). The pictures below show its age since the conjunction — not the day of the month. A crescent under a day old is very rarely seen; it usually becomes visible to the naked eye at about one to two days old, depending on the season, the sky and the location.

Crescent visibility is predicted with the Odeh (2006) criterion, built from 737 recorded crescent observations and one of the most reliable modern models.

Each evening is evaluated at the best time — sunset plus 4/9 of the lag time — the “best” time shown next to the viewing window. At that moment the site computes:

Arc of vision (ARCV)

How much higher the Moon is than the Sun, seen from the observer’s location without atmospheric refraction. The higher, the further the crescent is from the Sun’s glare.

Crescent width (W)

The width of the lit crescent in arcminutes: the Moon’s apparent radius from that location × (1 − cos ARCL), where ARCL is the angle between Sun and Moon. A wider crescent is brighter and easier to see.

These give a single value:
V = ARCV − (7.1651 − 6.3226W + 0.7319W² − 0.1018W³)

Zone A V ≥ 5.65

Easily visible to the naked eye.

Zone B 2.00 ≤ V < 5.65

Visible to the naked eye under perfect conditions — clear sky, a low unobstructed western horizon, and an experienced observer.

Zone C −0.96 ≤ V < 2.00

Binoculars or a telescope are likely needed to find it; once found it may be seen with the naked eye.

Zone D V < −0.96

Not visible, even with optical aid.

When estimating unreported months, the site counts zones A and B as naked-eye visible.

Lag time is the time between sunset and moonset: how long the crescent stays above the horizon after the Sun goes down. The viewing window runs from sunset to moonset, and the best chance is at 4/9 of the lag.

As a rule of thumb, a lag of at least 40 minutes is favourable for a naked-eye sighting, but the Odeh V value is the better guide because it also accounts for the crescent’s width and its distance from the Sun.

Under the Moon’s phase the site says where the Moon is right now — for example “Visible now — look SW (236°), 32° above the horizon (≈3½ fists at arm’s length)”. A closed fist held at arm’s length covers about 10° of sky, so stack fists up from the horizon. When the Moon is down it shows when and where it rises; a thin crescent in daylight is marked as lost in the Sun’s glare. This line only appears for the live view, not when previewing a date.

On phones, Find the Moon opens a compass: turn until the gold dot is under the pointer, then look up by the angle shown. Phone compasses are approximate, and the direction is not corrected for magnetic declination (in Israel, magnetic north is a few degrees east of true north).

The visibility zones assume a clear sky. For sighting evenings up to 16 days ahead the site also shows the weather forecast at the best viewing time, from Open-Meteo: low, mid and high cloud, visibility, chance of rain, and — up to 5 days ahead — dust and haze (aerosol optical depth, AOD). It checks Jerusalem and a point about 25 km toward where the Moon sets, because cloud or haze along the western horizon matters most.

The sky is rated clear, some cloud or haze, cloudy or hazy, or overcast/rain/dust, and combined with the zone into a chance of seeing the crescent. A zone B crescent needs perfect conditions, so even some cloud or haze makes a sighting unlikely.

Forecasts 7–16 days out are marked long-range and are much less reliable. For past evenings (when previewing an earlier date) the site shows the recorded sky instead.

The weather is advice only: it never changes a month or feast date. Clouds can hide a crescent that is really there, so only a reported sighting moves the calendar.

Each conjunction in the Data tab lists the zone for the first evening after it. When that evening is doubtful or impossible (C or D), the next evening’s zone follows — usually the evening the crescent is actually seen. This list is purely astronomical and ignores sighting reports.

• The zones themselves ignore weather; the separate weather forecast covers cloud, rain, dust and haze, but not light pollution, a blocked horizon or the observer’s experience.
• Sunset and moonset are the moments the upper edge disappears below a flat horizon, allowing for normal atmospheric refraction — the same convention as the US Naval Observatory and most almanacs. Odeh’s altitudes and angles are calculated without refraction, as his criterion expects. Hills, buildings or unusual air can shift what you see by a minute or two.
• Positions are calculated for Jerusalem’s elevation (754 m), or sea level for other locations.
• The criterion is statistical: borderline B and C evenings can go either way. A reported sighting always overrides the prediction.