How I built Lunary's birth chart reader

The birth chart feature is the core of Lunary. Every other feature either feeds from it or refers back to it. Building it properly took longer than I expected, mostly because "properly" turned out to have more requirements than I'd initially scoped. This is the story of how that feature was built: the calculation layer, the visual representation, the AI interpretation, and the iterations that got it from a rough prototype to something I'm proud of. What a birth chart actually contains A complete birth chart has more elements than most apps show. Lunary calculates and displays: Planets : Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto, and Chiron. Each has an ecliptic longitude (position in the zodiac), a latitude (angular distance from the ecliptic plane), a declination (angular distance from the celestial equator), and a speed (degrees per day, which indicates retrograde when negative). Points : The North Node (also called the True Node, computed from the Moon