Glossary term: Redshift

Description: This term can refer to three different effects: Doppler, cosmological, or gravitational redshift. Doppler redshift is the opposite of blueshift; in the case of redshift, the source emitting the electromagnetic radiation is moving away from the observer, and so the wavelength of the electromagnetic radiation is stretched to longer (redder) wavelengths. This is similar to the Doppler effect in the context of sound waves. Cosmological redshift is the result of electromagnetic radiation emitted by a source being stretched to longer wavelengths because of the physical expansion of space, unlike Doppler redshift which is due to relative motion. Gravitational redshift refers to the effect where the wavelength of electromagnetic radiation emitted from a source is stretched to longer wavelengths, or rather the associated photons lose energy as they try to leave a region (gravitational well) where the gravity is stronger.

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Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".

Related Media

Galaxies map, each dot is a galaxy, forming a web-like structure, the outer circle marks a distance of 2 billion light years

SDSS Redshift Map

Caption: This image shows a map of the distribution of galaxies and is based on redshift data from the Sloan Digital Sky Survey (SDSS). Redshift measurements provides information on the distances, positions and motions of the galaxies. The Earth is located at the center of the image, and each dot represents a galaxy. The outer circle represents a ""distance"" of about 2 billion light years. The idea of distance in cosmology is complex because the usual measurement of distance is the separation between two points in space at the same time. However, because of the speed of light, the further a distance, the farther back in time we are observing. The numbers on the outer circle are Right Ascension coordinates mapped onto a flat circle, and provides information on the position of the galaxies on the sky. The colours used represent the ages of the stars in the galaxies, the redder, more strongly clustered points represent galaxies comprising of older stars. The dark wedges that do not contain any dots are regions that were not mapped by the SDSS due to dust from the Milky Way galaxy obscuring the view.
Credit: M. Blanton and Sloan Digital Sky Survey credit link

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