Final answer:
The gas in a planetary nebula produces an emission spectrum characterized by bright emission lines.
Step-by-step explanation:
The gas in a planetary nebula produces an emission spectrum. The gas in a planetary nebula produces an emission spectrum characterized by bright emission lines.
This spectrum is characterized by bright emission lines that correspond to specific wavelengths of light. These emission lines are produced when electrons in the gas atoms are excited to higher energy levels and then transition back to lower energy levels, emitting light of specific wavelengths in the process.
For example, in the case of a planetary nebula, the greenish color typically comes from oxygen ions, which emit light at specific wavelengths in the green part of the spectrum.