To many astrophysicists, Stellar P larimetry is a Cinderella subject considered as being so insignificant and, at the same time, being so esoteric as to be ignored and left alone. Others have followed and developed the theme with an enthusiastic passion. There can be no doubt, however, that the study of polarization within Astronomy has a strong role to play either in its own right, or in combination with other observational tools, as a diagnostic for understanding the behaviour of celestial sources.
One problem is that the general topic of Polarization is frequently neglected in undergraduate teaching of Optics. It tends to be placed at the end of many basic courses and is then abandoned as time for presentation runs out. This may have a consequence that some Astronomers perhaps fight shy of becoming involved with its disciplines and connections to celestial sources. As time goes on, however, there is a more general awareness of what polarimetry can do for us in terms of gaining information on the geometry of astrophysical sources, and on the environments giving rise to polarized radiation. This treatise is offered to provide insight into the subject of Stellar P larimetry, from a basic understanding of polarized light, to the instrumentation required to measure polarization, and to a simple overview of polarimetry as applicable to stellar radiation, particularly in the optical region of the spectrum.
From the outset it may be noted that, in general, stellar polarimetric signals are very small. Using a lax terminology, it might be said that the task of recording data is a matter of looking for an exceedingly small number of photons that are polarized amongst a very much larger number which have random relationships with respect to each other, both in terms of ‘orientation’ and ‘phase’. With the right techniques, the task of teasing out the polarized photons can be accomplished with reward, leading to insight into some astrophysical objects that perhaps may not have been achievable by any other diagnostic technique.
