The Asterism

Inspired by Asterism (gemology) on Wikipedia

Built with Three.js · Custom ShaderMaterial · EffectComposer (UnrealBloomPass)

Techniques Rutile Ray Simulation · Cabochon Dome Geometry · Cursor-Driven Light Source · Additive Bloom

Direction The star is not in the stone. It is in the light.

Result A polished cabochon dome where your cursor becomes the light — rutile needles catch it and return a six-rayed star that follows you across the surface

The Story

Asterism comes from the Latin astrum — star. Inside certain sapphires, millions of rutile needles thinner than a wavelength of light align themselves along three crystal axes during billions of years of growth. When light strikes the polished dome of a cabochon-cut stone, each set of needles reflects a band of light perpendicular to its alignment. Three sets of parallel needles, 120 degrees apart, create six rays that converge wherever the light source sits.

The Star of India — 563 carats, two billion years old — has stars on both sides.

The star is not a thing inside the stone. It is the geometry of observation itself: the angle between your eye, the light, and the crystal’s hidden architecture. Move the light, and the star follows.

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The Take

The experience places you above a polished star sapphire cabochon. Your cursor is the light source. As you move across the dome, the six-rayed asterism glides beneath the surface — rays extending and contracting as the light angle changes. Bloom post-processing adds the characteristic soft glow of chatoyance. The narrative unfolds through timed text milestones as you explore.