NASA: Spectra and What They Can Tell Us -- Basic LessonThis tutorial from NASA's Goddard Space Center discusses the basics of star spectra and what scientists can learn from three types of spectra: continuous, emission, and absorption. It's appropriate for students with little or no previous knowledge of atomic spectra.
CK-12 Foundation: Atomic Emission SpectraThis short online tutorial provides an overview of how atoms gain energy to move from a ground state to an excited state. It discusses the discovery of atomic emission spectra and how early models led to proof of the quantized nature of light.
NASA: Spectral AnalysisThis is Part 2 of NASA Goddard Space Center's tutorial collection on how astronomers use spectral data in analyzing star composition. It shows a sample spectrum taken by the ASCA satellite, which used X-ray spectroscopy to produce a graph of light intensity vs. energy. It takes a deeper dive into how emission lines are detected using Compton Scattering and Synchrotron radiation techniques. Two short videos show release of a photon in Bremsstralung radiation (which occurs in supernova events) and the more common Compton scattering when a photon collides with an electron.
CK-12 Foundation: Spectral Lines of HydrogenIf you want to give beginning students a greater conceptual understanding of the transitions that occur when atoms change energy levels, try starting with this tutorial featuring the hydrogen atom. It explains how change in energy translates to the light of a particular frequency being emitted. (Includes a 1-minute animation of hydrogen gas being heated, emitting light, and refracting the light through a prism that produces an emission spectrum.)