PhosphorOccult

Predict stellar occultations for your exact location. Moon, planets, and asteroids. All computed on-device. No internet required. Part of the Phosphor Suite.

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: predictions update automatically overnight when your device is charging

CONFIGURATION

• Prediction window: 30 days to 5 years • Selectable occulting bodies: Moon, all planets, eight major asteroids — toggle individually • Manual location override for planning observations at remote sites • Phased computation: Moon results appear in seconds, other bodies compute silently in the background

Part of the Phosphor Suite. No ads. No tracking. No network calls. All computation performed locally. Your location is used only for predictions and never leaves your device.