D

Glossary

Astro2010: The 2010 National Research Council astronomy and astrophysics decadal survey.

Astronomy and Astrophysics Advisory Committee: A federal advisory committee chartered under the Federal Advisory Committee Act, the committee advises the National Science Foundation, the National Aeronautics and Space Administration, and the U.S. Department of Energy on selected issues within the fields of astronomy and astrophysics that are of mutual interest and concern to the agencies.

AXAF: See Chandra.

Baryon acoustic oscillation (BAO): Sound waves in the early universe generate fluctuations both in the cosmic microwave background spectrum and the matter (baryon) fluctuation spectrum.

Chandra: The Chandra X-ray Observatory, launched in 1999, one of NASA’s four Great Observatories.

Dark energy: Hypothetical form of energy that causes the present-day expansion of the universe to accelerate.

Dark Energy Survey (DES): A ground-based survey to study the nature of dark energy by observing the distributions of galaxies and clusters of galaxies, weak gravitational lensing, and supernovae.

Deep Space Network (DSN): NASA’s worldwide antenna network to support the exploration of the solar system.

Epoch of Reionization: The period during which the baryonic content of the universe is gradually ionized. The onset of reionization coincides with the emergence of the first ionizing (luminous) sources, at the end of the dark ages, and ends when the intergalactic medium is fully ionized.

Euclid: An medium-class mission selected by the European Space Agency for an upcoming launch to study dark energy.

European Space Agency (ESA): International organization of European states cooperating in space research and technology.

Exoplanet: An extrasolar planet, i.e., a planet orbiting a star other than the Sun.

Filter wheel: instrument component that contains filters to isolate particular wavelength regions.

Galaxy cluster: A large group of galaxies bound together gravitationally.



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D Glossary Astro2010: The 2010 National Research Council astronomy and astrophysics decadal survey. Astronomy and Astrophysics Advisory Committee: A federal advisory committee chartered under the Federal Advisory Committee Act, the committee advises the National Science Foundation, the National Aeronautics and Space Administration, and the U.S. Department of Energy on selected issues within the fields of astronomy and astrophysics that are of mutual interest and concern to the agencies. AXAF: See Chandra. Baryon acoustic oscillation (BAO): Sound waves in the early universe generate fluctuations both in the cosmic microwave background spectrum and the matter (baryon) fluctuation spectrum. Chandra: The Chandra X-ray Observatory, launched in 1999, one of NASA’s four Great Observatories. Dark energy: Hypothetical form of energy that causes the present-day expansion of the universe to accelerate. Dark Energy Survey (DES): A ground-based survey to study the nature of dark energy by observing the distributions of galaxies and clusters of galaxies, weak gravitational lensing, and supernovae. Deep Space Network (DSN): NASA’s worldwide antenna network to support the exploration of the solar system. Epoch of Reionization: The period during which the baryonic content of the universe is gradually ionized. The onset of reionization coincides with the emergence of the first ionizing (luminous) sources, at the end of the dark ages, and ends when the intergalactic medium is fully ionized. Euclid: An medium-class mission selected by the European Space Agency for an upcoming launch to study dark energy. European Space Agency (ESA): International organization of European states cooperating in space research and technology. Exoplanet: An extrasolar planet, i.e., a planet orbiting a star other than the Sun. Filter wheel: instrument component that contains filters to isolate particular wavelength regions. Galaxy cluster: A large group of galaxies bound together gravitationally. 39

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Gravitational lensing: Deflection of light by the gravitational potential associated with astronomical objects, such as stars, galaxies, and groups and clusters of galaxies. Two distinct regimes are important: (1) strong gravitational lensing, where the gravitational potential is deep enough to produce multiple images of a background source, and (2) weak gravitational lensing, where the gravitational potential distorts the appearance of background sources but does not create multiple images. Gravitational microlensing: An intensification of light from a background star produced by the gravity of a mass, such as another star or an exoplanet that is aligned almost exactly along the line of sight. Hubble Space Telescope (HST): Orbiting optical/ultraviolet/near-infrared space telescope launched in 1990 and refurbished at periodic intervals. Current Hubble Space Telescope cameras can image with ~0.1-arcsecond resolution and take ultraviolet spectra between 1100 and 3000 angstroms. Hyper Subprime Cam: A camera on Japan’s Subaru optical-infrared telescope, located at the summit of Mauna Kea on the island of Hawaii. Infrared: Light with wavelength longer than visible light but shorter than radio waves. Near-infrared refers to the wavelength range from ~1 to 5 microns, mid-infrared is ~5 to 20 microns, and far-infrared extends from ~20 microns to ~200 microns, where the submillimeter begins. James Webb Space Telescope (JWST): An infrared space observatory under construction, scheduled for launch in 2018 or later, which is the successor to the Hubble Space Telescope. Kepler: A NASA satellite mission with a photometric monitor of 150,000 stars looking for transits of extra-solar planets ranging in size from Jupiter down to sub-Neptune and Earth-like in radius. KIlo-Degree Survey (KIDS): A 1,500-square-degree public imaging survey with patches in both the Northern and Southern skies. The survey will use the OmegaCAM instrument mounted on the Very Large Telescope Survey Telescope. Large Synoptic Survey Telescope (LSST): A priority of the New Worlds, New Horizons (Astro2010) decadal survey, LSST is large aperture, wide field survey telescope and 3,200 megapixel camera to image faint astronomical objects across the sky. Medium-class (M-class): Medium-scale European Space Agency mission. Microlensing: See gravitational microlensing. Near-infrared (NIR): Wavelengths from ~1 to 5 microns. (Also see infrared). New Worlds, New Horizons (NWNH): The 2010 National Research Council astronomy and astrophysics decadal survey report, New Worlds, New Horizons in Astronomy and Astrophysics (The National Academies Press, Washington, D.C.). Optical: Wavelength range of light to which the human eye is sensitive, namely, 3,500 to 8,000 Å. Pan-STARRS-1: Panoramic Survey Telescope and Rapid Response System, a wide-field (1.8 meter) imaging facility being developed at the University of Hawaii’s Institute for Astronomy. 40

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Planck: A European Space Agency satellite launched in 2009 to map tiny fluctuations in the cosmic microwave background radiation. Point spread function (PSF): The point spread function describes the angular response of a telescope to a point-like source of light. Because of atmospheric turbulence and the finite resolving power of a telescope, light from point-like object is spread out in angle. Reaction wheels: Wheels that provide enhanced guiding and stabilization of a spacecraft. Redshift: The increase in wavelength of electromagnetic radiation (Doppler shift) caused by the motion of an object as described by the theory of special relativity, or by luminous material in a gravitational field as described by the general theory of relativity. In cosmology, it refers to the fractional increase in the wavelength of a photon received from a distant object, due to the expansion of the universe between emission and reception. Coupled with a cosmological model, redshifts can be used to determine the distance and look-back time of phenomena in the universe. Reionization: See Epoch of reionization. Science Definition Team (SDT): Team to help characterize a mission, in this case the WFIRST SDT. Sloan Digitized Sky Survey (SDSS): Dedicated 2.5-meter ground-based telescope supporting repeated multicolor images of a quarter of the sky. Space Infrared Telescope Facility (SIRTF): See Spitzer Space Telescope. Spitzer Space Telescope: NASA’s Space Infrared Telescope Facility, launched in 2003. Star cluster: A group of stars formed at about the same time. Very Large Telescope (VLT): Four 8-meter telescopes of the European Space Observatories, located in Chile. Weak lensing: Fluctuations in the large-scale distribution of matter produce variations in the “shape” of space that alter the path that light takes from a distant galaxy to our telescopes. This gravitational lensing changes the shape of a galaxy and makes it appear more elliptical. By measuring the shapes of large numbers of galaxies, astronomers can detect this “weak lensing” effect and infer the large-scale distribution of matter. WFIRST: Wide Field Infrared Survey Telescope, the top-ranked large space mission of NWNH. William Herschel Space Observatory: A European Space Agency satellite launched in 2009 to study the formation of stars and galaxies at far-infrared and submillimeter wavelengths. XMM-Newton: The European Space Agency’s X-ray Multi-Mirror mission, named after Sir Isaac Newton, is an orbiting X-ray observatory launched in 1999. It features a large collecting area for X-ray spectroscopy. 41