Full Idea
The theory of the expansion of the universe renders the red shift no longer puzzling, whereas he expansion of the universe is hardly rendered less puzzling by facts about the red shift.
Clarification
The 'red shift' is in the light coming from galaxies
Gist of Idea
Universe expansion explains the red shift, but not vice versa
Source
J.J.C. Smart (Explanation - Opening Address [1990], p.15)
Book Reference
'Explanation and Its Limits', ed/tr. Knowles,Dudley [CUP 1990], p.15
A Reaction
The direction of explanation is, I take it, made obvious by the direction of causation, with questions about what is 'puzzling' as mere side-effects.