High dispersion spectrum, looking at stars What is a high dispersion spectrum?
From what I understand it has to do with detecting where absorption lines are begin generated within a star, and then using the information to adjust the spectrograph to detect the full black body spectrum of the star.
 A: A "high dispersion" spectrum just means dispersing the light from a star across a large number of detector elements/pixels per unit wavelength.
With more pixels per unit wavelength, you are able to make better measurements of the strengths of absorption/emission lines (because it is more obvious what is continuum and what is line) and you can also make measurements of by how much the absorption/emission lines are broadened - for instance by the rotation of a star - and you are also able to make more precise measurements of the wavelengths of absorption lines, allowing more precise estimates of Doppler shifts.
A: Dispersion is basically the spectral equivalent to image resolution: How much/little information do you pack into one pixel. Higher dispersion/resolution allows for more detail, but requires more light to not be noisy/grainy, because a smaller fraction of the total light gets into each pixel. Lower resolution gives less detail, but gives a stronger signal in each pixel, which makes it better for fainter sources, where the high dispersion spectra would just be too noisy to give any useful information. 
