Light, in the GP’s example is also traceable back to a source. Observing an effect in a 3rd party isn’t directly attributable to anything without a plausible me

Light, in the GP’s example is also traceable back to a source. Observing an effect in a 3rd party isn’t directly attributable to anything without a plausible mechanism of action. Using light to detect stars as defense of dark matter isn’t a very strong argument.