Spectroscopy, Astrometry and Polarimetry
SpectroscopySpectroscopy concerns the study of the spectrum of light that many objects emit. It can be considered as a graphical representation of an object's brightness against photon energy (usually represented as wavelength or frequency). As you might imagine, a spectrum of an object yields far more information than a simpler measurement of its flux, so why would we consider photometry important? Firstly, we can perform photometry on objects that very often are too faint for spectroscopy. Also, photometry can be performed much more quickly and easily than spectroscopy. For example, a pair of images taken on the Liverpool Telescope might require one minute's exposure in each of two filters. This image might allow us to take measurements of tens to hundreds of stars. Spectroscopy on the other hand might require us to take an exposure of a few minutes duration simply to collect data for one star.
Polarimetry investigates the way light has been polarised – that is, the way the light has been affected by its creation in, or passage through, strong magnetic fields.
Astrometry deals with the exact positions that objects are in the sky, as exemplified by the current European Space Agency (ESA) Gaia mission.
Read more about the Liverpool Telescope.
Read some more advanced material on the electromagnetic spectrum.