ASTROMETRY / FIELD SERIES 02
THE SHAPE OF AN UNSEEN ORBIT
Fit the past. Predict the next star.
Gold rings are measured companion positions, labeled by year. Tune the orbit until each blue point meets its matching gold ring. Then test your model against one withheld year.
Observation ledger
Each row compares the measured position with the same year in your model. The final epoch stays sealed until validation.
How to fit an orbit · science & credits
Begin with node angle to rotate the pattern. Inclination squashes its apparent width; eccentricity changes both the curve and where the companion lies at each date. Adjust a little, watch whether the residual gets smaller, and revisit the other controls. A close-looking ellipse can still have the wrong timing.
All systems are synthetic and exactly solvable. Period, apparent semimajor axis, periastron time and periastron argument are supplied and fixed; three remaining elements are unknown. Positions come from Astronomia’s binary.position and kepler.kepler3 routines. The holdout is an additional model-consistency check, not statistical evidence from an independent real telescope. Units are arcseconds on the sky.
Astronomia by Sonia Keys and Commenthol, MIT, pinned at 71e16c9 (August 2025). Original challenge design and GPT-generated telescope plate. License.