(measurement of the strengths of different electromagnetic wavelengths)
Spectroscopy (or spectrometry) is the study of radiation
intensity as a
function of wavelength. It is the method for determining the
chemical composition of astronomical bodies as well as temperature
and radial motion.
Spectrography is virtually the same study but implies the use of
a spectrographic image, displaying the spectrum across its width.
Instruments operating at or near visible light typically use prisms or
gratings that angle light according to wavelength (dispersion).
Dispersion with prisms is small so often multiple prisms are used in
tandem, e.g., a triple prism spectrograph.
Photometry is like an extremely-low-resolution spectroscopy,
studying stars and astronomical bodies based upon just a few
bands. Its advantage is that it requires much less electromagnetic radiation,
thus can be used for more distant objects, and is also
multi-object by default.
Some instrument terms/classes:
Intensity at each wavelength is typically the item of interest
but there are also cases when polarization at each wavelength
if the item of interest.
Baryon Oscillation Spectroscopic Survey (BOSS)
Chandra X-ray Observatory (CXO)
Discovery Channel Telescope (DCT)
velocity dispersion (σ)
exoplanet eclipse light curve
Gran Telescopio Canarias (GTC)
imaging Fourier transform spectroscopy (IFTS)
integral field spectrograph
Nearby Supernova Factory (NSNF)
Rossiter-McLaughlin effect (RM effect)
Supernova Cosmology Project (SCP)
chromospheric activity index
stellar parameter determination
stellar temperature determination
2dF Galaxy Redshift Survey (2dFGRS)
James Webb Space Telescope (JWST)
William Herschel Telescope (WHT)