Grating Spectroscopes and How to Use Them Quotes

“prominent lines in the star’s spectrum these will show up. Likewise, if there is a planetary nebula or a bright emission nebula in the field these will only show as small points (due to the fine emission lines of the gases involved) rather than a spread out spectrum. This makes the grating a handy tool for finding faint planetary nebula. (See Chap. 7 for more detail.)”
― Ken M. Harrison, Grating Spectroscopes and How to Use Them