Redshift z is a fundamental astronomical parameter that measures how much electromagnetic radiation has been stretched to longer, redder wavelengths as it travels through expanding space. When light from distant galaxies reaches Earth, its wavelengths are systematically increased due to the expansion of the universe itself, creating a cosmological redshift proportional to distance. The redshift parameter z is defined as the fractional change in wavelength: z = (λ_observed - λ_emitted) / λ_emitted.</p><p>First discovered by Edwin Hubble in the 1920s, redshift revolutionized our understanding of cosmic expansion and led to the Big Bang theory. Modern observations have detected galaxies with redshifts exceeding z = 13, meaning we observe them as they existed just 400 million years after the Big Bang. Beyond cosmological redshift, astronomers also measure Doppler redshift from objects moving away from us and gravitational redshift caused by strong gravitational fields, making z a versatile tool for probing cosmic distances, velocities, and the fundamental structure of spacetime.
Practical Applications
Astronomers use redshift measurements to determine distances to galaxies, calculate the expansion rate of the universe (Hubble constant), and study cosmic evolution. High-redshift observations with telescopes like JWST reveal the earliest galaxies and star formation epochs. Redshift surveys map large-scale cosmic structure, while precise measurements help constrain dark energy properties and test cosmological models.