PhosphorOccult

PhosphorOccult — Occultation Prediction Instrument

Predict when the Moon, planets, and asteroids pass in front of stars. For your exact location. Computed entirely on your device.

PhosphorOccult is a precision occultation prediction tool for amateur astronomers, IOTA observers, and serious stargazers. It calculates upcoming stellar occultations — the moments when a solar system body passes directly in front of a distant star, causing it to vanish and reappear — using established astronomical algorithms and a catalogue of nearly 9,000 stars.

No internet connection required. No subscription. No data collection. One purchase, everything computed on-device.

WHAT IT PREDICTS

• Lunar occultations — the Moon passing in front of stars and planets, with immersion and emersion times accurate to seconds
• Planetary occultations — rare events where a planet occults a star (Venus, Jupiter, Saturn, and all major planets supported)
• Asteroid occultations — eight major asteroids (Ceres, Pallas, Vesta, Juno, and more) tracked as potential occulters

All predictions are topocentric — corrected for your exact latitude, longitude, and elevation. The Moon's parallax exceeds one degree; without this correction, predictions are useless. PhosphorOccult gets it right.

WHAT YOU SEE

• Events list — chronological predictions with contact times (UT), position angles, dark/bright limb classification, Moon altitude, and phase
• Polar sky plot — tonight's sky as a zenithal projection showing the Moon's track, planet positions, and occultation windows with hourly tick marks
• Event detail — full instrument readout with immersion/emersion data, position angles, elongation, and observer coordinates
• Telescope viewfinder — animated simulation of each event through an eyepiece, with time scrubber, pinch-to-zoom field of view, and Moon phase rendering
• Bodies browser — view all active occulting bodies and their predicted events

UNDER THE HOOD

• Lunar ephemeris: Jean Meeus, Astronomical Algorithms (ELP2000-82 series)
• Planetary ephemeris: VSOP87 truncated series and Keplerian orbital elements
• Star catalogue: 8,870 stars from ESA Hipparcos (public domain), bundled as a compact binary
• Prediction engine: coarse scan with pre-computed ephemeris tables, refined by bisection search to sub-second precision
• Background refresh: predictio