Observational cosmology

Observational cosmology uses astronomical measurements to investigate the universe’s large-scale structure, history, composition, and evolution.

Cosmic microwave background: The relic radiation released when the early universe became transparent, now observed as microwave light across the sky. Its temperature and polarization patterns encode conditions in the early universe.
Type Ia supernova: A thermonuclear explosion of a white dwarf whose light curve and spectrum help estimate its intrinsic luminosity. Their apparent faintness at high redshift revealed accelerated cosmic expansion.
ΛCDM model: The standard cosmological model, combining general relativity, cold dark matter, and a cosmological constant. It provides the baseline predictions that observations test.
Edwin Hubble: An American astronomer whose observations helped establish the relation between galaxy distance and recession velocity. His measurements helped make an expanding universe an observational conclusion.
Hubble tension: The disagreement between early-universe and late-universe measurements of the present expansion rate. It tests whether measurement systematics or extensions to the standard model explain discrepant results.
Redshift: The shift of light toward longer wavelengths, caused by relative motion, cosmic expansion, or gravitational effects. Galaxy redshifts provide a primary measure of cosmic expansion.
Galaxy redshift survey: A systematic catalog of galaxies with measured positions and redshifts. These surveys map large-scale structure and constrain cosmological models.
Cosmic distance measurement: The determination of astronomical distances from observable properties calibrated against known scales. Distances paired with redshifts reconstruct the expansion history.
Henrietta Swan Leavitt: An American astronomer who discovered a relation between Cepheid variable stars’ periods and intrinsic luminosities. Her relation enabled distance estimates to nearby galaxies.
Dark matter: Matter inferred from gravitational effects that does not emit or absorb detectable light. Multiple observations require more gravitating matter than luminous matter supplies.

Linked from 1 page

Robert HermanNarrower topic: The relic-radiation prediction exemplifies how a quantitative cosmological claim can later face direct measurement.