The key issue identified by Milton K. Munitz, whether cosmology should center on description or explanation, remains a central philosophical theme in the early twenty-first century. However, the context has changed dramatically since he wrote his entry, and that has changed the implications.

First, massive new data sets are available because of the extraordinary improvement of telescopes, detectors, and computer technology in the past three decades. Not only are optical, ultraviolet, and infrared observations of galaxies possible in determining luminosities and spectra with unprecedented sensitivity but radio, X-ray, and gamma ray sky surveys are also possible. Galaxies have been detected up to a redshift of 6 and many quasar-stellar objects as well as multiple images of distant gravitationally lensed galaxies have been identified. Besides large-scale number-count and redshift surveys, the background radiation spectrum at all wavelengths have been measured. A key feature has been identification of cosmic...