New Moon Day

The moon cycles through eight phases over approximately 29.5 days:

After conjunction (new moon), the crescent grows over the first few evenings. Day 1 is rarely sighted; naked-eye visibility typically begins on day 2 or 3 depending on sky conditions and location:

This site uses the Odeh (2006) criterion for predicting first crescent visibility, developed by Mohammad Odeh of the Jordanian Astronomical Society. It is considered one of the most accurate modern models, based on 737 recorded observations from around the world.

The model computes a V value from two key factors:

Arc of Vision (ARCV)

The altitude difference between the moon and the sun at sunset. A higher arc means the crescent is further above the sun's glare.

Crescent Width (W)

The topocentric width of the illuminated crescent in arcminutes. A wider crescent is brighter and easier to spot.

The formula is:
V = ARCV − (7.1651 − 6.3226W + 0.7319W² − 0.1018W³)

Zone A V ≥ 5.65

The crescent is easily visible to the naked eye. No special conditions or experience needed.

Zone B 2.00 ≤ V < 5.65

Visible under perfect conditions — clear skies, low humidity, an unobstructed western horizon, and an experienced observer.

Zone C −0.96 ≤ V < 2.00

Optical aid (binoculars or telescope) is likely needed to locate the crescent. Once found, it may be visible to the naked eye.

Zone D V < −0.96

The crescent is not visible, even with a telescope. The moon is too close to the sun or the crescent is too thin.

Lag time is the difference between moonset and sunset. It tells you how long the crescent moon remains above the horizon after the sun goes down. A longer lag time means a larger window to spot the crescent before it too sets below the horizon.

Generally, a lag time of at least 40 minutes is considered favourable for naked-eye sighting, though the Odeh V criterion is a more comprehensive predictor since it also accounts for the crescent's brightness and angular separation from the sun.

Jerusalem holds deep significance for biblical and lunar calendar traditions. The sighting of the new crescent moon from the land of Israel has historically been used to declare the beginning of a new month. This site calculates visibility specifically for Jerusalem's coordinates (31.77°N, 35.21°E).