A Scientific Assessment of a New Technology Orbital Telescope (1995) / Chapter Skim
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Pages 68-77
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From page 68... ...
These tables are initially generated by making observations of wavefronts from a distant source at a variety of temperatures and orientations. Adaptive optics A set of techniques to adjust the shape of mirrors on time scales of a fraction of a second to correct for rapid fluctuations in image quality.
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From page 69... ...
A unit of angle corresponding to 1/3600th of a degree; 1/60th of an arc minute. An arc second is approximately the size of a penny viewed from about 2.5 miles.
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From page 70... ...
The spherical envelope of gas and dust surrounding the nucleus of an active comet A volatile-rich body that develops a transient atmosphere as it orbits the Sun Observed comets usually have highly elliptical orbits, many approaching parabolic, although many comets in the Kuiper Disk are likely to have nearly circular orbits, as are many of the currently unobservable comets in the Oort cloud. When a comet comes near the Sun, some of its material vaporizes, forming a large head of tenuous gas, and often a tail.
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From page 71... ...
High-Z telescope A proposed 4-meter space telescope optimized for cosmological observations HST Hubble Space Telescope: a 2.4-meter-aperture, optical/ultraviolet telescope developed by NASA and the European Space Agency Infrared astronomy The study of astronomical objects using intermediate-wavelength radiation to which the atmosphere is mostly opaque and the human eye insensitive. Humans sense infra red energy as heat.
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From page 72... ...
Stars as faint as magnitude 28 can be seen with powerful terrestrial or spaceborne telescopes. mas Milliarc second: one-thousandth of an arc second Molniya orbit A highly eccentric and inclined orbit with a nominal period of 12 hours used mainly by Russian telecommunication satellites NASA National Aeronautics and Space Administration
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From page 73... ...
A typical image from a single chip in the Hubble Space Telescope is a square with 800 x 800 discrete pixels. Point-spread function The variation of intensity with distance from the center of an image of a true point source.
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From page 74... ...
Refigure Changing the shape of an optical surface Resolution The ability of an instrument to discern fine detail SDIO Strategic Defense Initiative Organization: the predecessor of BMDO SIRTF Space Infrared Telescope Facility: NASA's proposed 1-meter-aperture, cryogenically cooled, infrared space telescope STIS Space Telescope Imaging Spectrograph: a second-generation instrument that will be installed in the Hubble Space Telescope in 1997 Strehl ratio A measure of the quality of an optical instrument equal to the ratio of the amplitude of the point-spread function to that of an equivalent, ideal instrument STScI Space Telescope Science Institute Supernova An explosive death of a star whose tremendous energy output causes its expanding debris to glow brightly enough to be seen at extragalactic distances for weeks or months thereafter TGBNTOO Task Group on BMDO New Technology Orbital Observatory Titan IV A large U.S launch vehicle used primarily by the Department of Defense Type I Supernova A type of supernova that occurs in a binary star system containing a white dwarf. All such events are believed to have the same intrinsic brightness and so can be used as distance indicators.
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From page 75... ...
GLOSSARY 75 Wavefront A surface of constant phase, that is, an imaginary surface linking the crests or troughs of the rays of light from a common source WFPC Wide Field/Planetary Camera: the primary camera used by the Hubble Space Tele scope before its first servicing mission WFPC2 Wide FieldlPlanetary Camera 2: the primary camera currently being used on the Hubble Space Telescope YSOs Young stellar objects z Redshift: the increase in the wavelength of a spectral line from an astronomical body relative to its value measured in a terrestrial laboratory. The wavelength shift is then given by the factor (1 + z)
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