= Lick Observatory
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<Lick Observatory> is an astronomical observing site associated with optical <spectroscopy> and precision measurements of stellar motion. In the <Lick Observatory iodine-cell radial-velocity method>, a cell places known <iodine> <absorption> on the stellar beam, allowing instrumental changes and a stellar <Doppler shift> to be fitted together.
This apparatus illustrates why a spectral shift cannot be read independently of <calibration>. The reference and stellar <spectra> pass through the same optical system, and their combined image must be modelled with the instrumental line profile. Repeated measurements then test an orbital signal rather than merely identifying one shifted spectral line.
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