(device to measure light by wavelength across its spectrum)
The term Spectrometer is for a device that measures a spectrum,
e.g., the Intensity of light at different Wavelengths.
As such, a Spectroscope or Spectrograph is a spectrometer.
Those two terms originally distinguished between a device that
you look through (Spectroscope) and one that recorded the spectrum
on film (Spectrograph), but
modern advanced instruments virtually always focus the spectrum on
a CCD or similar sensor, allowing the spectral data to be
transmitted, recorded and analyzed electronically, and any of the
three terms may be used.
The terms may be used for analyzers
of any part of the Electromagnetic Radiation spectrum, but when used for other
than Visible Light, that is usually mentioned, e.g., the phrase
The term Mass Spectrometer is used for a device that measures
the relative number of Particles entering according to mass.
Thus it does not concern light or other EMR.
Space probes often include mass spectrometers to analyze material
collected, such as Dust.
Information about the masses provide clues to its makeup.
Advanced Composition Explorer (ACE)
Atacama Submillimeter Telescope Experiment (ASTE)
Berkeley Extreme and Far-UV Spectrometer (BEFS)
CCAT Prime (CCAT-p)
Compton Gamma Ray Observatory (CGRO)
Chandra X-ray Observatory (CXO)
European Southern Observatory Very Large Telescope (ESO VLT)
Green Bank Telescope (GBT)
Herschel Space Observatory
Hubble Space Telescope (HST)
Integral Field Spectrograph
Infrared Space Observatory (ISO)
James Clerk Maxwell Telescope (JCMT)
Mars Global Surveyor (MGS)
New Horizons (NF1)
Solar Maximum Mission (SMM)
Solar and Heliospheric Observatory (SOHO)
Spectral Power Distribution (SPD)
Spitzer Space Telescope (SST)
Tomographic Ionized-Carbon Mapping Experiment (TIME)
Thirty Meter Telescope (TMT)
Telescopio Nazionale Galileo (TNG)
Tubingen Ultraviolet Echelle Spectrometer (TUES)
United Kingdom Infrared Telescope (UKIRT)
James Webb Space Telescope (JWST)