Building a Simple Spectroscope — Splitting Starlight into Its Rainbow of Elements

A spectroscope splits light into its component colours — its spectrum — revealing what elements produced the light. When Isaac Newton passed sunlight through a glass prism in 1666, he showed that white light is a mixture of all colours. In 1814, Joseph von Fraunhofer examined the Sun's spectrum more carefully and discovered dark lines crossing the rainbow — specific colours that were missing. Each element absorbs or emits light at precise wavelengths: hydrogen produces red, blue-green, blue-violet, and violet lines; sodium produces a bright yellow doublet; iron produces hundreds of fine lines. By matching these spectral fingerprints, astronomers can determine what stars are made of without ever visiting them — the birth of astrophysics. This blueprint builds a functional prism spectroscope from a glass prism and simple materials, capable of resolving the Fraunhofer lines in sunlight and the emission lines of common elements in flame tests.