Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992sciam.267...54f&link_type=abstract
Scientific American (ISSN 0036-8733), vol. 267, no. 5, p. 54-60.
Astronomy and Astrophysics
Astronomy
1
Astronomical Models, Cepheid Variables, Cosmology, Hubble Constant, Universe, Dark Matter, Galactic Evolution, Gravitational Lenses, Red Shift
Scientific paper
This paper examines evidence and estimates of the size and expansion rate of the universe emphasizing the limitations of the measurements and methods. The estimates are based on measurements of distances to galaxies (particularly Cepheids) to assess their movements, and the disputed value of the Hubble constant is discussed in this context. Solid-state CCDs facilitate the remeasurement of distances to nearby galaxies, and several methods are reviewed for computing the distances. The Hubble constant can be determined by: (1) evaluating the graininess of galactic images; (2) comparing apparent luminosities; (3) calculating gravitational lensing effects; or (4) comparing the luminosities of type Ia supernovae. Cepheid measurements were used to calculate the Hubble constant by means of three methods yielding a consistent value of about 80 km/s/Mpc. This constrains the universe age to about 12 billion years but also raises questions about theoretical models of galaxy formation.
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