They are seen in light called H - alpha, about the same color as a red laser pointer, produced by hot hydrogen gas in the solar atmosphere. (nso.edu)
Using Keck Observatory's powerful infrared spectrograph called MOSFIRE, the team dated the galaxy by detecting its Lyman - alpha emission line — a signature of hot hydrogen gas heated by strong ultraviolet emission from newly born stars. (keckobservatory.org)
WHAM telescope The Wisconsin Hydrogen - Alpha Mapping telescope focuses on the light emitted by hot hydrogen gas. (discovermagazine.com)