TITLE: Caelestis Atlas — A Map of the Heavens, Engraved MDCCL
PROMPT: Build a single-file antique celestial atlas: a circular star chart of the northern hemisphere rendered as inline SVG on a deep indigo plate (#101a33) with gold (#c9a227) constellations, a zodiac ring, an eight-point compass rose, a parchment cartouche and a constellation legend. The chart lives in a 900x900 viewBox: a radial sky gradient disc, concentric declination circles in #6b7a99 at 12-20% opacity, radial spokes every 30 degrees, and a 360-tick zodiac scale between r=372 and r=430 where every fifth tick is longer; the zodiac ring carries the twelve three-letter names (ARI TAU GEM CAN LEO VIR LIB SCO SAG CAP AQU PIS) placed tangentially with a rotate(angle+90) transform and spins once every 420 seconds via a CSS keyframe on a transform-box:view-box group. Twelve hand-authored constellations (Ursa Major, Orion, Cassiopeia, Cygnus, Lyra, Draco, Scorpius, Pegasus, Andromeda, Cetus, Aquila, Perseus) are defined as polar [radius, degrees] star lists with explicit link pairs, converted to cartesian points, and injected as innerHTML strings into existing SVG groups - never createElementNS. Each constellation is one group containing a wide transparent hit path, a 30%-opacity gold polyline, star circles and an italic serif label. A comet with a gradient tail crosses the chart every 32 seconds. Parchment (#f2e8d5) cartouche at the top with small-caps letterspaced Georgia, a two-column legend at the lower left with ui-monospace coordinates, and an aged vignette of inset shadows and a slowly drifting grain layer. Palette: #101a33, #c9a227, #f2e8d5, #6b7a99, #8c1c13.
DESCRIPTION: An 18th-century engraved map of the heavens, redrawn as a living web page. The chart reads first: a gold zodiac ring, concentric graticule circles, four hundred faint stars and a dozen gold constellations drawn from hand-authored polar coordinates. Over the top sits a parchment cartouche in small-caps Georgia with generous tracking, and at the lower left a two-column legend lists each constellation with its right ascension and declination in monospace. An eight-point compass rose anchors the lower right. The plate feels aged through layered grain, an inset vignette with a faint red burn at the edges, and a comet that crosses the sky every half minute.
TECHNIQUES: Runtime SVG built entirely by assigning innerHTML strings to existing SVG group elements; polar star placement from hand-authored seeded data; gold constellation polylines highlighted by animating stroke-dashoffset from path length to zero (getTotalLength) for a drawing-on effect; conic-segment compass rose as static inline polygons; parchment texture from layered repeating gradients with a slow transform drift; CSS-animated twinkling star subset and a slow zodiac-ring rotation using transform-box: view-box; pointer-capture drag rotation and wheel zoom composed into a single translate/rotate/scale transform attribute.
INTERACTION: Hovering a constellation - its lines, stars or chart label - highlights it, re-draws its line with a dashoffset sweep, and prints its name and coordinates in the bottom readout. Clicking a constellation locks it on with a brighter white-gold line and a persistent glow. The legend rows mirror both behaviours and clicking a row locks that constellation. Dragging on the chart rotates the whole map; the wheel zooms between 0.72x and 1.9x. The zodiac ring keeps rotating very slowly on its own. With prefers-reduced-motion the ring, comet, grain drift and twinkle animations are switched off.