Spectroscopy
While photometric data can be beautiful to look at, spectroscopic data tells us a lot more about the objects we want to explore. Spectra provide us with measurements of an object’s brightness in smaller bins of wavelength which helps us learn more about their composition, distance and can be essential to accurately classify objects.
Spectra are graphs of intensity against wavelength. Smaller values of wavelength correspond to higher-energy photons and bluer colours. Correspondingly, larger values of wavelength indicate redder colours and lower-energy photons.
Features of Spectra
Continuum
Every object produces a continuous spectrum with some light emitted at every wavelength. However, no spectrum is completely smooth
Absorption lines
Dips in intensity at certain wavelengths create lines that fall below the continuum. These are wavelengths where light has been absorbed by gas or dust that is between us and the source of light. They can be used to determine the composition of the material that absorbed the light.
Emission lines
Peaks in intensity above the continuum. These are wavelengths where light has been emitted by hot gas. The specific wavelengths at which this light is emitted indicate the composition of the gas.
In order to obtain the spectra of many objects at once the SDSS produced specially drilled aluminium plates with 1000 holes, to capture light from 1000 objects, in the next section we will go into more detail on how these plates work.
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All image credits to SDSS