(spectrum of radiation passing through a substance)
Transmission spectroscopy is study of a substance through
its effect on the spectrum of electromagnetic radiation (EMR) passing through.
Absorption spectroscopy also fits this definition, but
transmission spectroscopy typically means something more, such as
the use of differential spectroscopy. In astronomy, the term
is used sometimes for techniques analyzing of atmospheres, the
interstellar medium, and clouds. It is one of the terms used for data
collection regarding an extra-solar planet atmosphere through spectroscopy
of the host star's EMR that has passed through it.