water lines

Water lines (spectral lines) in astrophysics fall under at least two classifications:

• emission lines from water masers.
• absorption lines from EMR passing through gaseous or liquid water.

Water absorption, like that of many compounds, produces many lines affecting significant bands of the spectrum,

The presence of water vapor in extra-solar planet atmospheres can be detected by transmission spectroscopy through recognizable water lines. Water vapor's presence in Earth's atmosphere significantly limits microwave, millimeter, submillimeter, and infrared observations from the ground, motivating observations from space as well as from high, dry ground locations.