Armillary Sphere: Celestial Circles (2D Meridian Diagram)

A flat companion to the 3D armillary sphere: instead of spinning bronze rings in space, this is the classic astronomer's meridian-plane diagram — the same horizon, equator, polar axis and tropics, drawn edge-on as straight lines and chords in the plane you're looking at. Move the latitude slider to relocate the celestial pole and tilt the equator; move the day-of-year slider to slide the sun's declination circle between the tropics and watch its noon altitude, day length and sunrise/sunset time update from real spherical-astronomy formulas.