Recombination light
M42
Measured
Hydrogen recombination radiation. H II regions shine when electrons rejoin protons. M42 is the nearby visible case. The 21 cm line is a different hydrogen clock.
PhotoNASA, ESA, M. Robberto (STScI/ESA) and the Hubble Space Telescope Orion Treasury Project TeamPUBLIC DOMAIN
The Orion Nebula glows by hydrogen recombination. Catalogue seat M42. The process is physics. The forty-two is the Messier number, not a measured angle of recombination.
What it supports
A real radiative process. Door to M42 and to the 21 cm line. Two hydrogen offices, not one law.
What it does not
Not 42 eV. Not a second rainbow. Not the last-scattering radius (~42.7 Mly).
ExactnessCatalogue position
Form42
Unitprocess
Strengthhard