Stellar occultations by trans-Neptunian objects are the sharpest tool for measuring their sizes and shapes. When Haumea passes in front of a star, the star's light disappears for a duration that maps directly to the object's chord length. Multiple observers at different locations measure different chords, and the set of chords reconstructs the object's projected shape.
The challenge is prediction. Haumea is 50 AU away, and its angular size is about 30 milliarcseconds. Predicting where Haumea's shadow falls on Earth requires knowing its position to better than its own angular diameter — tens of milliarcseconds in absolute astrometry. At this precision, systematic errors in star catalogs and TNO ephemerides dominate over random errors.
The paper predicts stellar occultations by Haumea through 2030, incorporating the latest Gaia astrometry for background stars and updated orbital solutions for Haumea. The predicted event of May 4, 2026 is highlighted as an especially favorable geometry: a bright star, a wide shadow track across populated regions, and sufficient lead time for coordinated observations.
The predictions are probabilistic — each event has a predicted shadow path and an uncertainty region, typically tens of kilometers wide. The uncertainty is dominated by Haumea's orbital uncertainty, which propagates to shadow-path uncertainty on Earth's surface. Reducing this uncertainty requires either more astrometric observations of Haumea or successful occultation detections (which constrain the orbit retroactively). Each successful observation improves all future predictions — the measurement strengthens the tool that enables the measurement.