Question: Why does the poet say stars are like diamonds? — Manoj Jejurkar, Earth
Answer: Poets often use the metaphor of stars as diamonds because they share many qualities. Both are bright, both scintillate (twinkle or sparkle), and both produce a spectrum of colors. The video shows a rotating diamond next to Vega, the fifth brightest star in the sky. Vega was photographed at a high magnification to accentuate the twinkling.
These beautiful visual effects are a result of refraction, the "bending" of light rays as they pass from one transparent substance into another. For a star, the refraction is caused by variations in Earth's atmosphere. For a diamond, it's caused by the internal lattice of carbon atoms.
In my May 7, 2012 post I show a video of Sirius (the brightest star in the sky) twinkling. All stars twinkle like that, especially when they're lower in elevation and you see them through thicker air. As the star's light passes through our turbulent atmosphere it's affected by variations like pockets of air at different temperatures and densities. This will cause the light to change directions (twinkle) and disperse (separate into colors). Both Vega and Sirius are intrinsically blue-white stars, but if you watch them twinkle you'll see other colors flashing on and off.
With a diamond the process is slightly different. The internal lattice of atoms is fixed, so a diamond at rest will not scintillate (unless the light source is moving). But it will show bright and dark facets in a spectrum of colors.
Also, light entering a diamond will be reflected internally (often multiple times) before leaving the diamond and heading for your eyes. The geometry of the facets cut into diamonds are designed to enhance this effect. The longer the light remains in the diamond the greater the dispersion, and the more colors in the sparkle. Gem cutters learned, by trial and error, how to optimize this effect in the 1300s to 1400s when better cutting tools became available.
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