Question: What does spectroscopy study and focus on?
About the article "Astrophysics", section "History".

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Spectroscopy measures the interaction of the molecules with electromagnetic radiation.
Spectroscopy consists of many different applications such as atomic absorption spectroscopy, atomic emission spectroscopy, ultraviolet-visible spectroscopy, x-ray fluorescence spectroscopy, infrared spectroscopy, Raman spectroscopy, nuclear magnetic resonance spectroscopy, photoemission spectroscopy, Mössbauer spectroscopy and so on. 
Instrumental methods.
Spectroscopy measures the interaction of the molecules with electromagnetic radiation.
Spectroscopy consists of many different applications such as atomic absorption spectroscopy, atomic emission spectroscopy, ultraviolet-visible spectroscopy, x-ray fluorescence spectroscopy, infrared spectroscopy, Raman spectroscopy, dual polarisation interferometry, nuclear magnetic resonance spectroscopy, photoemission spectroscopy, Mössbauer spectroscopy and so on. 
Positron annihilation spectroscopy (PAS) or sometimes specifically referred to as Positron annihilation lifetime spectroscopy (PALS) is a non-destructive spectroscopy technique to study voids and defects in solids.  
In fMRS, depending on the focus of the study, either single-voxel or multi-voxel spectroscopic technique can be used.
In single-voxel fMRS the selection of the volume of interest (VOI) is often done by running a functional magnetic resonance imaging (fMRI) study prior to fMRS to localize the brain region activated by the task.
Single-voxel spectroscopy requires shorter acquisition times; therefore it is more suitable for fMRS studies where high temporal resolution is needed and where the volume of interest is known.
Multi-voxel spectroscopy provides information about group of voxels and data can be presented in 2D or 3D images, but it requires longer acquisition times and therefore temporal resolution is decreased.
Multi-voxel spectroscopy usually is performed when the specific volume of interest is not known or it is important to study metabolite dynamics in a larger brain region. 
Other types of spectroscopy are distinguished by specific applications or implementations: Acoustic resonance spectroscopy is based on sound waves primarily in the audible and ultrasonic regions Auger spectroscopy is a method used to study surfaces of materials on a micro-scale.
It is often used in connection with electron microscopy.
Cavity ring down spectroscopy Circular Dichroism spectroscopy Coherent anti-Stokes Raman spectroscopy (CARS) is a recent technique that has high sensitivity and powerful applications for "in vivo" spectroscopy and imaging.
Cold vapour atomic fluorescence spectroscopy Correlation spectroscopy encompasses several types of two-dimensional NMR spectroscopy.
Deep-level transient spectroscopy measures concentration and analyzes parameters of electrically active defects in semiconducting materials Dual polarisation interferometry measures the real and imaginary components of the complex refractive index EPR spectroscopy Force spectroscopy Fourier transform spectroscopy is an efficient method for processing spectra data obtained using interferometers.
Fourier transform infrared spectroscopy (FTIR) is a common implementation of infrared spectroscopy.
NMR also employs Fourier transforms.
Hadron spectroscopy studies the energy/mass spectrum of hadrons according to spin, parity, and other particle properties.
Baryon spectroscopy and meson spectroscopy are both types of hadron spectroscopy.
Hyperspectral imaging is a method to create a complete picture of the environment or various objects, each pixel containing a full visible, VNIR, NIR, or infrared spectrum.
Inelastic electron tunneling spectroscopy (IETS) uses the changes in current due to inelastic electron-vibration interaction at specific energies that can also measure optically forbidden transitions.
Inelastic neutron scattering is similar to Raman spectroscopy, but uses neutrons instead of photons.
Laser-Induced Breakdown Spectroscopy (LIBS), also called Laser-induced plasma spectrometry (LIPS) Laser spectroscopy uses tunable lasers and other types of coherent emission sources, such as optical parametric oscillators, for selective excitation of atomic or molecular species.
Mass spectroscopy is an historical term used to refer to mass spectrometry.
Current recommendations are to use the latter term.
Use of the term mass spectroscopy originated in the use of phosphor screens to detect ions.
Mössbauer spectroscopy probes the properties of specific isotopic nuclei in different atomic environments by analyzing the resonant absorption of gamma-rays.
See also Mössbauer effect.
Neutron spin echo spectroscopy measures internal dynamics in proteins and other soft matter systems Photoacoustic spectroscopy measures the sound waves produced upon the absorption of radiation.
Photoemission spectroscopy Photothermal spectroscopy measures heat evolved upon absorption of radiation.
Pump-probe spectroscopy can use ultrafast laser pulses to measure reaction intermediates in the femtosecond timescale.
Raman optical activity spectroscopy exploits Raman scattering and optical activity effects to reveal detailed information on chiral centers in molecules.
Raman spectroscopy Saturated spectroscopy Scanning tunneling spectroscopy Spectrophotometry Time-resolved spectroscopy measures the decay rate(s) of excited states using various spectroscopic methods.
Time-Stretch Spectroscopy Thermal infrared spectroscopy measures thermal radiation emitted from materials and surfaces and is used to determine the type of bonds present in a sample as well as their lattice environment.
The techniques are widely used by organic chemists, mineralogists, and planetary scientists.
Ultraviolet photoelectron spectroscopy (UPS) Video spectroscopy Vibrational circular dichroism spectroscopy X-ray photoelectron spectroscopy (XPS)