Many properties of light are explained, but not all. The speed of light coming from space has not yet been measured, all measurements are made for light emitted by luminaries on Earth.
Light coming from space originates from moving particles and passes through magnetic and gravitational fields on its way to us. The measurement of this speed of light is described in the following article.
Why should we measure the speed of light from space? Because it has not yet been measured and it can be measured, to prove the speed of light to the students with a measurement and because the results of the measurement provide opportunities for insight into dark matter. Dark matter has eluded us for too long.
Example: The diffraction grating shows the Doppler shift of the spectral lines. It is different with an optical prism. An optical prism does not detect the Doppler shift of spectral lines. The wavelength of light remains the same regardless of the speed of the light source. Observations show that Doppler’s law only affects the frequency of light, not its wavelength.
