MASS spectroscopy is the spectroscopy of MASSES. Bunch of ions of different isotopes is accelerated in electric field and then passes via magnetic field. Different masses travel at circles with different radii and strike a photoplate or CCD at different places producing mass distribution spectrum.

It is just a spectroscopy (seeing different colors and bands/lines) which IDs various elements in distant stars. It can be in visible light, in IR, in UV, x-ray, gamma-ray, or radio bands.


And position of lines not only tells the element, but how and where the source is moving, or rotating, or jetting, etc. And how strong is magnetic field or gravity around it. And many other interesting things.