Physics
Spectroscopy Fundamentals
Quick fact
Helium was first discovered in the Sun’s spectrum in 1868, years before it was found on Earth, demonstrating spectroscopy's power to detect elements across the cosmos.
Why this is interesting
Have you ever wondered how scientists can identify the chemical composition of a star trillions of miles away, simply by analyzing its light?
Read the full explanation
Understanding Spectroscopy Fundamentals
Imagine each element or molecule has a unique set of 'fingerprints' made of light. When light passes through a substance, certain wavelengths are absorbed—these absorbed wavelengths correspond exactly to the energy differences between that substance’s atomic or molecular energy levels. The resulting pattern of dark lines (absorption spectrum) or bright lines (emission spectrum) acts like a barcode, identifying the substance. Just as you can identify a person by their fingerprints, you can identify a material by its spectral fingerprint.
A deeper explanation
Spectroscopy works because electrons in atoms and molecules can only exist at specific energy levels. When a photon (a particle of light) has an energy exactly matching the gap between two energy levels, it can be absorbed, boosting the electron to a higher level. Conversely, an excited electron falling back to a lower level emits a photon of that exact energy. Since energy is related to wavelength (E = hc/λ), the set of allowed transitions produces a unique pattern of spectral lines. This fundamental quantum mechanical behavior allows us to probe the composition, temperature, density, and motion of matter—from a simple salt flame test to analyzing the atmospheres of exoplanets.