Editing Lyman-alpha (section)

==Observation==
Since the hydrogen Lyman-alpha radiation is strongly absorbed by the air, its observation in laboratory requires use of vacuumed spectroscopic systems. For the same reason, Lyman-alpha astronomy is ordinarily carried out by satellite-borne instruments, except for observing extremely distant sources whose [[redshift]]s allow the line to penetrate the [[Earth]] atmosphere.

The line was also observed in [[antihydrogen]].<ref>{{cite journal |title=Observation of the 1S–2P Lyman-α transition in antihydrogen |first1=M. |last1=Ahmadi |display-authors=etal |journal=Nature |volume=560 |issue=7720 |pages=211–215 |date=22 August 2018 |doi=10.1038/s41586-018-0435-1 |pmid=30135588 |pmc=6786973 |doi-access=free }}</ref> Within the experimental uncertainties, the measured frequency is equal to that of hydrogen, in agreement with predictions of [[quantum electrodynamics]].