Stellar Radiation & Stellar Types
Objects of different temperatures emit spectra that peak at different wavelengths (as indicated by Wien's Law) so that hotter objects emit most of their radiation at shorter wavelengths, appearing bluer, while cooler objects emit most of their radiation at longer wavelengths, therefore appearing redder.
Scientists use a spectrograph to split the spectrum of the star they are studying. Examining spectra allows astronomers to find out what stars are made of, their structures and their past.
When looking at light that has travelled through the atmosphere of a star, (effectively a low density gas) scientists observe black lines in the spectrum, known as Fraunhofer lines. These lines correspond to selective absorption of the radiation at specific wavelengths due to the various elements existing in the stellar atmosphere. Stars are made up of the same elements that are found here on Earth, but in different proportions. The spectrum of a star, therefore, displays a massive number of absorption lines, which reveal a detailed fingerprint of the composition of the star. For example, over 100 000 absorption lines are visible in the Sun's spectrum.