The Dust Penetrated Universe: Hidden Symmetries
A simple analogy may be in order: a ship approaches a harbor at night. The captain does not see the harbor in much detail. His view is dominated by the brilliant light of the harbor lighthouse, just as our view of the spirals is dominated in visible light by the brilliant hot stars and the regions of star formation. Now imagine that the night is foggy. The captain sees even less of the harbor, just as our view of galaxies is affected by the fog of cosmic dust. So the Captain's view of the harbor is misleading because of two critical issues: once by the brilliance of the optical light beaming from the lighthouse, and secondly by the fog enveloping the actual lighthouse. How strikingly does our full moon mask the presence of fainter stars (Figure 129).