Reference

Allan Sandage made several significant contributions to astronomy, notably in the field of observational cosmology. Here are some of his key contributions:

1. Hubble Constant and Age of the Universe: Allan Sandage was one of the first astronomers to provide reasonably accurate values for the Hubble constant, which relates to the rate at which the universe is expanding. His work allowed for better estimates of the age of the universe. (Source)

2. Discovery of Quasars: Sandage played an active role in the discovery of quasars, which are extremely luminous active galactic nuclei. These enigmatic objects were first detected by radio astronomers in the late 1950s. (Source)

3. Redshift Surveys: He conducted major redshift surveys of galaxies, which helped create a three-dimensional map of the universe. This work was crucial for understanding the large-scale structure of the cosmos. (Source)

4. Cosmic Expansion and Deceleration Parameter: In 1961, Sandage explained the cosmic expansion rate and the deceleration parameter, both critical for understanding the dynamics of the universe's expansion. (Source)

5. Type Ia Supernovae as Standard Candles: He helped establish Type Ia supernovae as standard candles for measuring cosmic distances, which is pivotal in the field of distance scaling in astronomy. (Source)

Here is an image of Allan Sandage:

These contributions have greatly advanced our understanding of the universe and its underlying physics.