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Astronomy 4-5.4
| Term | Definition |
|---|---|
| electromagnetic radiation | changing electric and magnetic fields that travel through space and transfer energy from one place to another; examples are light and radio waves |
| wavelength | the distance between successive peaks or troughs of a wave, usually represented by a lowercase Greek lambda |
| nanometer | a unit of distance equaling one-billionth of a meter, commonly used to measure the wavelength of light |
| angstrom | a unit of distance commonly used to measure the wavelength of light |
| ultraviolet | the portion of the electromagnetic spectrum with wavelengths shorter than violet light, between visible light and X-rays |
| x-rays | electromagnetic waves with wavelengths shorter than ultraviolet light |
| gamma rays | the shortest-wavelength electromagnetic waves |
| photon | a quantum of electromagnetic energy that carries an amount of energy that depends inversely on its wavelength |
| atmospheric window | wavelength region in which our atmosphere is transparent - at visual, radio, and some infrared wavelengths |
| refracting telescope | a telescope that forms images by bending light with a lens |
| reflecting telescope | a telescope that forms images by reflecting light with a mirror |
| primary lens | in a refracting telescope, the largest lens |
| primary mirror | in a reflecting telescope, the largest mirror |
| eyepiece | a short-focal-length lens used to enlarge the image in a telescope. the lens nearest the eye |
| focal length | of a lens or mirror is the distance from that lens or mirror to the point where it focuses parallel rays of light |
| chromatic aberration | a distortion found in refracting telescopes because lenses focus different colors at slightly different distances. images are consequently surrounded by color fringes |
| optical telescope | telescope that gathers visible light |
| radio telescope | telescope that gathers radio radiation |
| light-gathering power | the ability of a telescope to collect light; proportional to the area of the telescope's primary lens or mirror |
| resolving power | the ability of a telescope to reveal fine detail. depends on the diameter of the telescope's primary lens or mirror |
| diffraction fringe | blurred fringe surrounding any image, caused by the wave properties of light. because of this, no image detail smaller than the fringe can be seen |
| interferometer | separated telescopes combined to produce a virtual telescope with the resolution of a much larger-diameter telescope |
| seeing | atmospheric conditions on a given night. when the atmosphere is unsteady, producing blurred images, the seeing is said to be poor |
| adaptive optics | a computer-controlled optical system in an astronomical telescope used to partially correct for seeing |
| magnifying power | the ability of a telescope to make an image larger |
| light pollution | the illumination of the night sky by waste light from cities and outdoor lighting, which prevents the observation of faint objects |
| sidereal tracking | the continuous movement of a telescope to keep it pointed at a star as Earth rotates |
| secondary mirror | can reflect the light through a hole in the primary mirror |
| cassegrain focus | focal arrangement that may be the most common form of astronomical telescope |
| newtonian focus | arrangement that Isaac Newton used in his first reflecting telescope, inconvenient for large telescopes |
| schmidt-cassegrain focus | a thin correcting plate improves the image but is too slightly curved to introduce serious chromatic aberration |
| photographic plate | the first image-recording device used with telescopes; it records the brightness of objects ,but with only moderate precision |
| photometer | sensitive astronomical instrument that measures the brightness of individual objects very precisely |
| charge-coupled device | an electronic device consisting of a large array of light-sensitive elements used to record very faint images |
| array detector | device for collecting and recording electromagnetic radiation using multiple individual detectors arrayed on the surface of a chip; for example, a CCD electronic camera |
| digitized | converted to numerical data that can be read directly into a computer memory for later analysis |
| false-color image | a representation of graphical data with added or enhanced color to reveal detail |
| spectrograph | a device that separates light by wavelengths to produce a spectrum |
| spectrum | a range of electromagnetic radiation spread into its component wavelengths (colors); for example, a rainbow |
| grating | a piece of material in which numerous microscopic parallel lines are scribed. light encountering a grating is dispersed to form a spectrum |
| spectral line | a feature in a spectrum at a specific wavelength produced by the absorption or emission of light by certain atoms |
| transits of venus | rare occasions when venus can be seen as a tiny dot directly between Earth and the sun |
| density | mass per volume |
| atom | the smallest unit of a chemical element, consisting of a nucleus containing protons and neutrons plus a surrounding cloud of electrons |
| nucleus | the central core of an atom containing protons and neutrons that carries a net positive charge |
| proton | a positively charged atomic particle contained in the nucleus of a hydrogen atom |
| neutron | an atomic particle with no charge and about the same mass as a proton |
| isotope | a form of an atom with the same number of protons but a different number of neutrons |
| electron | low-mass atomic particle carrying a negative charge |
| molecule | two or more atoms bonded together |
| heat | energy contained in matter in the form of agitation of its particles |
| temperature | a measure of the agitation among the atoms and molecules of a material |
| Kelvin temperature | a temperature scale using Celsius degrees and based on zero being equal to absolute zero |
| absolute zero | he theoretical lowest possible temperature at which a material contains no extractable heat energy. zero on the Kelvin temperature scale |
| blackbody radiation | spectrum of radiation emitted by an ideal perfect radiator. the spectrum is continuous and its characteristics depend only on the object's temperature |
| wavelength of maximum intensity | the wavelength at which the radiation emitted by a glowing object is most intense. depends inversely on the object's temperature |
| wien's law | the hotter a glowing object is, the shorter will be its wavelength of maximum intensity, inversely proportional to its temperature |
| stefan-boltzmann law | hotter objects emit more energy than cooler objects of the same size, in proportion to the fourth power of temperature |
| photosphere | the bright visible surface of the sun |
| sunspot | relatively dark spot on the sun that contains intense magnetic fields |
| granulation | the fine structure of bright grains with dark edges covering the sun's surface |
| convection | circulation in a fluid driven by heat. hot material rises and cool material sinks |
| coulomb force | the electrostatic force of repulsion or attraction between charged bodies |
| ion | an atom that has lost or gained one or more electrons |
| ionization | the process in which atoms lose or gain electrons |
| binding energy | the energy needed to pull an electron away from its atom |
| quantum mechanics | the study of behavior of atoms and atomic particles |
| permitted orbit | one of the unique orbits that an electron may occupy in an atom |
| energy level | one of a number of states an electron may occupy in an atom, depending on its binding energy |
| excited atom | an atom in which an electron has moved from a lower to a higher energy level |
| ground state | the lowest permitted electron energy level in an atom |
| quantum jump | jumps of electrons from one orbit or energy state to another |
| doppler effect | the change in the wavelength of radiation due to relative radial motion of source and observer |
| blueshift | a doppler shift toward shorter wavelengths caused by a velocity of approach |
| redshift | a doppler shift toward longer wavelengths caused by a velocity of recession |
| radial velocity | that component of an object's velocity directed away from or toward the observer |
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