Spectrographic dating

The analysis for the most part relates to design and not to applications.

Overall this is an ideal text to have when doing various spectrographic work.

If a plate is observed on more than one MJD, the fibers will be replugged; thus a given fiber ID on different MJDs will correspond to different objects on the sky.

Finally, no target can be closer than 100 arcsec to the center of the plate, because of the center post on the plate.

Still others had intentionally repeated spectroscopic observations, with the same plate being re-observed several times.

Thus, in addition to a plate number, identifying an SDSS spectrum requires knowing the (modified Julian date) on which that spectrum was observed.

All previous SDSS spectroscopic data (Data Releases 1-8), including all SEGUE and SEGUE-2 data, was taken with the SDSS spectrograph.

With Data Release 9, we release the first data from a new instrument: the BOSS spectrograph.

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