Keywords • Advanced Camera For Surveys (ACS) • Association of Universities for Research in Astronomy, Inc. (AURA) • Charge-Coupled Device (CCD) • Digital Image • European Space Agency (ESA) • Faint Object Camera (FOC) • Faint Object Spectrograph (FOS) • Filter • Filter Wheels • Fine Guidance Sensors (FGS) • Fixed Head Star Trackers (FHST) • Goddard High Resolution Spectrograph (GHRS) • Goddard Space Flight Center (GSFC) • Guide Star • Gyroscope • High Speed Photometer (HSP) • Hubble Space Telescope (HST) • Image Intensifier • Marshall Space Flight Center (MSFC) • Multi-Layer Insulation (MLI) • National Aeronautics And Space Administration (NASA) • Near Infrared Camera And Multi-Object Spectrometer (NICMOS) • Pickoff Mirror • Pixel • Primary Mirror • Prime Focus • Reaction Wheel • Secondary Mirror • Solar Arrays • Space Shuttle • Space Telescope Imaging Spectrograph (STIS) • Space Telescope Science Institute (STScI) • Tracking and Data Relay Satellite System (TDRSS) • Wide Field / Planetary Camera (WF/PC) • Wide Field and Planetary Camera 2 (WFPC2) Advanced Camera For Surveys (ACS) An optical camera aboard the Hubble Space Telescope that covers twice the area, has twice the sharpness, and is up to ten times more efficient than the telescopefs Wide Field and Planetary Camera 2. The camera's wavelength range spans from ultraviolet to near-infrared light. The camera's sharp eye and broader viewing area enable astronomers to study the life cycles of galaxies in the remotest regions of the cosmos. Astronauts installed the camera aboard the telescope in March 2002. Back to Contents Association of Universities for Research in Astronomy, Inc. (AURA) A consortium of educational and other non-profit institutions that operates world-class astronomical observatories. Members include five international affiliates and 29 U.S. institutions, including the Space Telescope Science Institute in Baltimore, Maryland, the science operations center for NASA's Hubble Space Telescope. Back to Contents Charge-Coupled Device (CCD) An electronic detector that records visible light from stars and galaxies to make photographs. These detectors are very sensitive to the extremely faint light of distant galaxies. They can see objects that are 1,000 million times fainter than the eye can see. CCDs are electronic circuits composed of light-sensitive picture elements (pixels), tiny cells that, placed together, resemble mesh on a screen door. The same CCD technology is used in digital cameras. The Hubble Space Telescope's Wide Field and Planetary Camera 2 has four CCDs; each contains 640,000 pixels. The light collected by each pixel is translated into a number. These numbers (all 2,560,000 of them) are sent to ground-based computers, which convert them into an image. Back to Contents Digital Image A visible image that is recorded by an electronic detector and subdivided into small picture elements (pixels). Each element is assigned a number that corresponds to the brightness recorded at its physical location on the detector. Computer software converts the numerical information into a visual image. The Hubble Space Telescope records digital images. Back to Contents European Space Agency (ESA) A fifteen-member consortium of European countries for the design, development, and deployment of satellites. The Space Telescope — European Coordinating Facility (ST-ECF) supports the European astronomical community in exploiting the research opportunities provided by the Earth-orbiting Hubble Space Telescope. The ESA members are Austria, Belgium, Denmark, Finland, France, Germany, Ireland, Italy, the Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, and the United Kingdom, with Canada as a cooperating state. Back to Contents Faint Object Camera (FOC) An instrument aboard the Hubble Space Telescope that recorded high-resolution images of faint celestial objects in deep space. Built by the European Space Agency, the camera collected ultraviolet and visible light from celestial objects. The camera served as Hubble's "telephoto lens” — recording the most detailed images over a small field of view. The FOC's resolution allowed Hubble to single out individual stars in distant star clusters. The instrument was replaced in March 2002 during Servicing Mission 3B. Back to Contents Faint Object Spectrograph (FOS) An instrument aboard the Hubble Space Telescope that acted like a prism to separate light from the cosmos into its component colors, providing a wavelength "fingerprint” of the object being observed. Such information yields clues about an object's temperature, chemical composition, density, and motion. Spectrographic observations also reveal changes in celestial objects as the universe evolves. The instrument was replaced in February 1997 during the Second Servicing Mission. Back to Contents Filter A type of window that absorbs certain colors of light while allowing others to pass through. Astronomers use filters to observe how celestial objects appear in certain colors of light or to reduce the light of exceptionally bright objects. For example, a pair of sunglasses acts as a type of filter, reducing the amount of incoming light while still allowing some light to pass through to the eyes. Back to Contents Filter Wheels Rotating wheels in a telescope instrument that allow specific colors of light from a celestial object to pass through and form an image on the detector. The Wide Field and Planetary Camera 2 aboard the Hubble Space Telescope has 12 filter wheels, each of which holds four filters. Fine Guidance Sensors (FGS) Targeting devices aboard the Hubble Space Telescope that lock onto "guide stars” and measure their positions relative to the object being viewed. Adjustments based on these precise readings keep Hubble pointed in the right direction. The sensors also are used to perform celestial measurements. Back to Contents Fixed Head Star Trackers (FHST) Small telescopes with wide fields of view that are aboard the Hubble Space Telescope and used in conjunction with the Fine Guidance Sensors. The star trackers locate the bright stars that are used to orient the telescope for scientific observations. Back to Contents Goddard High Resolution Spectrograph (GHRS) A science instrument aboard the Hubble Space Telescope that made finely detailed spectroscopic observations of ultraviolet sources. The GHRS was removed from Hubble in February 1997 and replaced with the Space Telescope Imaging Spectrograph. Back to Contents Goddard Space Flight Center (GSFC) NASA's flight control center in Greenbelt, Maryland, which receives data from orbiting observatories such as the Hubble Space Telescope (HST). HST digital data are then relayed to the Space Telescope Science Institute in Baltimore, Maryland, where they are interpreted into pictures. Goddard also conducts scientific investigations, develops and operates space systems, and works toward the advancement of space science technologies. Back to Contents Guide Star A star that a telescope's guidance system locks onto to ensure that a celestial object is followed and observed as the telescope moves, owing either to the Earth's rotation or the telescope's orbital trajectory. The Hubble Space Telescope uses two of its three Fine Guidance Sensors to detect and lock onto guide stars. The telescope's science operations center has more than 15 million guide stars in its database — the Guide Star Catalogue. Back to Contents Gyroscope A spinning wheel mounted on a non-stationary frame that stabilizes and points a space-based observatory. This spinning wheel resists applied external forces and tends to retain its original orientation in space. For example, balancing on a moving bicycle is easier than balancing on a stationary one because of this tendency. Gyroscopes are used in navigational instruments for aircraft, satellites, and ships. The Hubble Space Telescope has six gyroscopes on board for navigation and sighting purposes. Back to Contents High Speed Photometer (HSP) An original science instrument aboard the Hubble Space Telescope that made very rapid photometric observations of celestial objects in near-ultraviolet to visible light. The instrument was removed in December 1993 during the First Servicing Mission. Back to Contents Hubble Space Telescope (HST) An orbiting telescope that collects light from celestial objects in visible, near-ultraviolet, and near-infrared wavelengths. The telescope was launched April 24, 1990 aboard the NASA Space Shuttle Discovery. The 11,110kg, tube-shaped telescope is 15.9m long and 4.2m wide, while its solar panels measure 2.4 x 12.1m. It orbits the Earth every 96 minutes and is mainly powered by the sunlight collected by its two solar arrays. The telescope's primary mirror is 2.4m wide. The telescope is operated jointly by the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA). HST is one of the many NASA Origins Missions, which include current satellites such as the Far Ultraviolet Space Explorer (FUSE) and future space observatories such as the Next Generation Space Telescope (NGST). Back to Contents Image Intensifier A device capable of intensifying light from a faint source so that it may be more easily detected. Back to Contents Marshall Space Flight Center (MSFC) NASA center overseeing the research, development, and implementation of three primary areas essential to space flight: reusable space transportation systems, generation and communication of new scientific knowledge, and management of all space lab activities. Located in Huntsville, Alabama, the center aided in the design, development, and construction of the Hubble Space Telescope. Back to Contents Multi-Layer Insulation (MLI) A "skin" or blanket of insulation covering the Hubble Space Telescope, which protects the observatory from temperature extremes. This insulation protects the telescope from the cold of outer space and also reflects sunlight so that the telescope does not become too warm. The MLI on Hubble is made up of many layers of aluminized Kapton, with an outer layer of aluminized Teflon. Back to Contents National Aeronautics And Space Administration (NASA) A Federal agency created on July 29, 1958 after President Dwight Eisenhower signed the National Aeronautics and Space Act of 1958. NASA coordinates space exploration efforts as well as traditional aeronautical research functions. Back to Contents Near Infrared Camera And Multi-Object Spectrometer (NICMOS) An instrument that sees objects in near-infrared wavelengths, which are slightly longer than the wavelengths of visible light. (Human eyes cannot see infrared light.) NICMOS is actually three cameras in one, each with different fields of view. Many secrets about the birth of stars, solar systems, and galaxies are revealed in infrared light, which can penetrate the interstellar gas and dust that blocks visible light. In addition, light from the most distant objects in the universe "shifts” into infrared wavelengths due to the universe's expansion. By studying objects and phenomena in this spectral region, astronomers probe our universe's past, present, and future; and learn how galaxies, stars, and planetary systems form. Astronauts installed NICMOS aboard the Hubble Space Telescope in February 1997 during the Second Servicing Mission. Back to Contents Pickoff Mirror One of four flat mirrors inside the Hubble Space Telescope. Each mirror is tilted at a 45-degree angle to the incoming light, diverting a small portion of it to the optical detectors or to one of the fine guidance sensors. Back to Contents Pixel A light-sensitive picture element on a charge-coupled device (CCD) or some other kind of digital camera. A pixel is a tiny cell that, placed together with other pixels, resembles the mesh on a screen door. The Hubble Space Telescope's Wide Field and Planetary Camera 2 has four CCDs, each containing 640,000 pixels. Each pixel collects light from a celestial object and converts it into a number. The numbers (all 2,560,000 of them) are sent to ground-based computers, which convert them into an image. The greater number of pixels, the sharper the image. Back to Contents Primary Mirror A large mirror in a reflecting telescope that captures light from celestial objects and focuses it toward a smaller secondary mirror. The primary mirror in the Hubble Space Telescope measures 94.5 inches (2.4 meters) in diameter. Back to Contents Prime Focus The location where light reflected from the primary mirror of a reflecting telescope comes into focus. Placing a secondary mirror in the light path allows the light to be focused elsewhere, in a more convenient location for the science instruments. Back to Contents Reaction Wheel One of four spinning flywheels aboard the Hubble Space Telescope. The flywheels work together to make the observatory rotate either more rapidly or less rapidly toward a new target. Back to Contents Secondary Mirror A small mirror in a reflecting telescope that redirects light from the larger primary mirror toward the light-sensitive scientific instruments. In a Cassegrain-type telescope like the Hubble Space Telescope, the secondary mirror is slightly convex and directs light from the primary mirror back through a hole in the center of the primary mirror. Hubble's secondary mirror measures 12.2 inches (0.3 meters) in diameter. Back to Contents Solar Arrays Two rigid, wing-like arrays of solar panels that convert sunlight directly into electricity to operate the Hubble Space Telescope's scientific instruments, computers, and radio transmitters. Some of the energy generated is stored in onboard batteries so the telescope can operate while in Earth's shadow (which is about 36 minutes out of each 97-minute orbit). The solar arrays are designed for replacement by visiting astronauts during servicing missions. Back to Contents Space Shuttle A reusable U.S. spacecraft operated by astronauts and used to transport cargo, such as satellites, into space. The spacecraft uses rockets to launch into space, but it lands like an airplane. A space shuttle carried the Hubble Space Telescope into space in 1990. Astronauts aboard subsequent space shuttles have visited the telescope to service it. Back to Contents Space Telescope Imaging Spectrograph (STIS) An instrument that acts like a prism to separate light from the cosmos into its component colors, providing a wavelength "fingerprint” of the object being observed. The information yields clues about an object's temperature, chemical composition, density, and motion. Spectrographic observations also reveal changes in celestial objects as the universe evolves. Astronauts installed STIS aboard the Hubble Space Telescope in February 1997 during the Second Servicing Mission. STIS spans ultraviolet, visible, and near-infrared wavelengths. The spectrograph can sample 500 points along a celestial object simultaneously. Back to Contents Space Telescope Science Institute (STScI) The astronomical research center responsible for operating the Hubble Space Telescope as an international scientific observatory. Located in Baltimore, Maryland, STScI is managed by AURA (Association of Universities for Research in Astronomy) under contract to the National Aeronautics and Space Administration (NASA) and the National Science Foundation (NSF). Back to Contents Tracking and Data Relay Satellite System (TDRSS) A network of four communication satellites used to relay data and commands to and from U.S. spacecraft, including the Hubble Space Telescope. The Goddard Space Flight Center provides the day-to-day management and operations of TDRSS, the first space-based global tracking system. Back to Contents Wide Field / Planetary Camera (WF/PC) A collection of eight separate, yet interconnected, cameras originally used as the main optical instrument on the Hubble Space Telescope. Four cameras were used in tandem to observe in either wide-field, low-resolution mode or narrow-field, high-resolution ("planetary") mode. The Wide Field and Planetary Camera 2 replaced the WF/PC during the December 1993 servicing mission. Back to Contents Wide Field and Planetary Camera 2 (WFPC2) The Hubble Space Telescope's "workhorse"; instrument, WFPC2 snaps high-resolution images of faraway objects. Its 48 filters allow scientists to study precise wavelengths of light and to sense a range of wavelengths from ultraviolet to near-infrared light. The instrument has four CCDs (charge-coupled devices), which collect information from stars and galaxies to make photographs. WFPC2 was installed aboard the Hubble telescope during the December 1993 servicing mission. Back to Contents |