Stellar Spectrums

Stellar Spectra

A Stellar Spectrum is the range of colours and wavelengths of light emitted by a star.
The spectrum acts like a fingerprint, giving unique information about the star’s composition, temperature, and velocity.

Spectra can be continuous, emission or absorption spectra, based on how the light and colours are arranged.
A continuous spectrum is an uninterrupted band of colours, like a rainbow. It is produced by hot, dense objects like a star’s surface.
An emission spectrum is a series of coloured lines on a black background, produced by hot, low-density gases.
An absorption spectrum, like a star’s spectrum, shows a continuous spectrum with dark lines. These lines are caused by atoms or molecules absorbing certain wavelengths of light.

Spectral lines are unique to the elements present in a star, serving as an elemental ID. Each element leaves a unique pattern of lines, or signature, on the spectrum.
Absorption lines, also known as Fraunhofer lines, are formed when the outer layers of a star absorb certain wavelengths of light from its inner layers.

Using spectral lines and other features of the spectrum, astronomers can determine key properties like a star’s chemical composition and surface temperature.
Spectral classification sorts stars mainly based on temperature and features of the spectrum. The OBAFGKM scale (from hottest to coolest stars) is a popular system used.

The Doppler Effect in stellar spectra helps to determine if a star is moving towards or away from us due to the blueshift or redshift of lines in the spectrum.
Blueshift occurs when a star is moving towards us, compressing light waves and shifting the spectrum towards the blue end.
Redshift occurs when a star is moving away, stretching light waves and shifting the spectrum towards the red end.

A key application of star spectra is the Hertzsprung-Russell Diagram (HR Diagram), a graph that plots stars’ brightness against their surface temperature.
By plotting stars on the HR Diagram, astronomers can understand different stages of stellar evolution and categorise stars into groups like main sequence, giants and white dwarfs.

Spectroscopy, the study of stellar spectra, originated in the 19th century.
Pioneers like Joseph von Fraunhofer, Gustav Kirchhoff and Robert Bunsen helped to understand spectral lines and connect them with chemical elements.
The knowledge and techniques of spectroscopy have greatly enhanced our understanding of the universe.