Astronomers can tell the components of stars by looking at the spectral emission lines. By looking at the spectrum, astronomers can see how much light it emits at different wavelengths without going to the star itself.
The colours and intensity of the lines in the spectrum are determined by the movement of the electrons. When the electrons are excited, they ‘jump’ and change orbit and give off photons. The more the number of photons doing this at the same time will result the higher the intensity. Different jumps give different colours and frequencies.
Types of Spectra
1. Continuous Spectra
This is what is seen from sources of light and are comprised of infinite lines.
2. Discrete Spectrum
These spectrums give discrete lines which indicate the presence of elements in gaseous objects. When an element is present, its lines show up as dark lines in the stellar spectrum. By matching the lines discrete spectral lines found in stars to that of observed in the laboratory, the elements can be identified. Below are some of the lines of elements as seen in the spectrums.
3. Absorption Spectra
These appear to be ‘holes’ in the continuous spectrum from a star. This is caused by the cooler atmosphere of the star absorbing some of the light from the core of the star radiating out. The pattern of the dark areas in absorption spectra will tell what type of the element is present in the atmosphere.
Red shift & Blue shift
Stars moving towards us will appear to exhibit a red shift due to the Doppler effect. This means that their spectra will appear to shift towards the left instead of being at their supposed positions. Stars moving away from us will appear to exhibit a blue shift instead and the spectra will appear to move to the right. Quasars or quasi-stellar objects are estimated to be at the edge of the universe at 13 billion light years due to their enormous blue shift.
Measuring Binary stars
The spectra of stars appear to overlap in binary system. The rotation of the binary stars can thus be measured by observing the changes in the spectrum over time.
Alpha Crucis, the brightest star of the southern cross, Crux in the bottom centre of this image, consists of two stars of magnitudes 1.3 and 1.8 as well as a wider 5th magnitude star.
Life Cycles of Stars | Diffuse Nebula | Main-Sequence Stars | Red Giants after Main-Sequence | Death of a Low Mass Star | Death of a High-Mass Star | Star Families | Magnitude Scale | Measuring Stellar Distances | Classification of stars | Wien's Law and Stefan-Boltzmannn Law for a Blackbody | Stellar Spectra