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Visibility Predictor

Crescent Moon Sighting Calculator — Yallop & Odeh models

Location & Date
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Calculation Date
Times
Sunset
Best Viewing
Moonset
Conjunction
Visibility Predictions
Astronomical Parameters
At best viewing time
Moon age
Lag time
Illumination
Moon altitude
Moon azimuth
Crescent width (W)
Other
Sun azimuth at sunset
Sunset
Moonset
DAZ
ARCV
ARCL
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Parameter Guide
Conjunction
Moment of new moon when Sun and Moon align. Moon age is measured from this point.
Moon age
Hours since conjunction. Crescents under ~15 h are rarely visible; most sightings occur after 18 h.
Lag time
Minutes between sunset and moonset. Longer lag gives more time to sight the crescent before it sets.
Moon altitude
Height of the moon's center above the horizon at best viewing time. Higher altitude is easier to see.
Moon / Sun azimuth
Compass direction (0°=N, 90°=E, 180°=S, 270°=W). Look toward the sun's azimuth just after sunset to find the crescent.
Illumination
Percentage of the moon's disk lit by the sun. Near new moon this is very small (often <1%).
ARCV
Arc of vision — vertical angle between moon and sun centers. The primary driver in Yallop and Odeh models.
DAZ
Azimuth difference between moon and sun. A larger DAZ can lift the crescent higher above the horizon glare.
ARCL
Arc of light (elongation) — total angular separation between moon and sun centers. Determines crescent thickness.
Crescent width (W)
Width of the illuminated sliver in arcminutes. Wider means a brighter, thicker crescent that is easier to spot.