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This page gives you easy access to GIF
images of individual spectra. Select a plate and a fiber on the
form below. If you want to save an image to disk, use this service.
If you want to use this image on your website, please feel free to
do so, but give us an acknowledgement.
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The SDSS project uses 5-color images to detect millions of objects
(eventually over 300 million stars and galaxies) over the whole sky. As soon
as these objects are observed, a sophisticated software algorithm selects targets
for further studies. Using another instrument, we take detailed spectra,
measurements of the energy given off by an object as a function of its wavelength.
These spectra tell much more about an object than its image. Spectra can
be used to estimate a
galaxy's distance or chemical composition, or to determine a star's age.
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The measured spectra are processed automatically by our software. The software
identifies individual features in the spectra: emission and absorption lines. Comparing
the observed lines to a list of laboratory measurements, we can infer the relative velocity of the
galaxy or star with respect to Earth. If the object is moving away from us, its spectral lines are shifted
towards longer wavelengths; this is the famous Doppler shift. Since the universe
expands uniformly, objects that are twice as far are receding from us twice as fast.
We can use this fact to measure distances to galaxies, and eventually to create a three-dimensional
map of the universe.
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On the images of the spectra you can see annotations: these show the different spectral
lines that our software has found. The type of object and its redshift is written on the bottom of
the image as well.
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