Test 2: Astrophysics

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Wave
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The disturbance or oscillation (of a physical quantity), that travels through matter or space, accompanied by a transfer of energy.
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Wavelength
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the distance between successive crests of a wave, especially points in a sound wave or electromagnetic wave.
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Period (T)
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Time needed for one complete cycle of vibration to pass a given point. As the frequency of a wave increases, the period of the wave decreases.
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Frequency (f)
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Number of occurrences of a repeating event per unit time.
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Amplitude
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The maximum displacement or distance moved by a point on a vibrating body or wave measured from its equilibrium position. It is equal to one-half the length of the vibration path.
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Electromagnetic Wave
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Waves which can travel through the vacuum of outer space
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Blackbody (Continuous) Spectrum
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A black body in thermal equilibrium (that is, at a constant temperature) emits electromagnetic radiation called black-body radiation. The radiation is emitted according to Planck’s law, meaning that it has a spectrum that is determined by the temperature alone.
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Kelvin
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273.16 K
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Luminosity
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The luminosity of an object is defined as the total energy per unit time emitted by the object. Another term for luminosity is power.
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Doppler Effect
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the change in frequency of a wave (or other periodic event) for an observer moving relative to its source.
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Red Shift
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When an object moves away from us, its light waves are stretched into lower frequencies or longer wavelengths, and we say that the light is redshifted. In the visible portion of the electromagnetic spectrum, blue light has the highest frequency and red light has the lowest.
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Blue Shift
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A blueshift is any decrease in wavelength, with a corresponding increase in frequency, of electromagnetic waves; the opposite effect is referred to as redshift. In visible light, this shifts the color from the red end of the spectrum to the blue end.
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Spectrometer
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Spectrometers are optical instruments that can detect spectral lines and measure their wavelength or intensity
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Emission (Line) Spectrum
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The spectrum of frequencies of electromagnetic radiation emitted due to an atom or molecule making a transition from a high energy state to a lower energy state.
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Absorption
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absorption of electromagnetic radiation is the way in which the energy of a photon is taken up by matter, typically the electrons of an atom. Thus, the electromagnetic energy is transformed into internal energy of the absorber, for example thermal energy.
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Spectrum
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in optics, the arrangement according to wavelength of visible, ultraviolet, and infrared light.
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Photon
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a particle representing a quantum of light or other electromagnetic radiation. A photon carries energy proportional to the radiation frequency but has zero rest mass.
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Kirchoff’s Current Law
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This fundamental law results from the conservation of charge. It applies to a junction or node in a circuit — a point in the circuit where charge has several possible paths to travel.
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Kirchoff’s Voltage Law
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Sum of all voltage drops and rises in a closed loop equals zero
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Reflecting Telescopes
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a telescope in which a mirror is used to collect and focus light.
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Refracting Telescopes
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a telescope that uses a converging lens to collect light.
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Focal Length
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the distance between the center of a lens or curved mirror and its focus. the equivalent distance in a compound lens or telescope.
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Focal Plane
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the plane through the focus perpendicular to the axis of a mirror or lens.
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Prime Focus
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The observer/camera is at the focal point (shown as a red X). In a prime focus design no secondary optics are used, the image is accessed at the focal point of the primary mirror.
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Chromatic Aberration
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the material effect produced by the refraction of different wavelengths of electromagnetic radiation through slightly different angles, resulting in a failure to focus. It causes colored fringes in the images produced by uncorrected lenses.
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Spherical Aberration
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a loss of definition in the image arising from the surface geometry of a spherical mirror or lens.
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Light Gathering Power
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A telescope’s light gathering power and ability to resolve small detail is directly related to the diameter (or aperture) of its objective (the primary lens or mirror that collects and focuses the light). The larger the objective, the more light the telescope collects and the finer detail it resolves.
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Resolution
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Angular resolution, or spatial resolution, describes the ability of any image-forming device such as an optical or radio telescope, a microscope, a camera, or an eye, to distinguish small details of an object, thereby making it a major determinant of image resolution.
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Resolving Power
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the ability of an optical instrument or type of film to separate or distinguish small or closely adjacent images. the ability of an electronic device to produce images that can be distinguished.
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“Seing”
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refers to the blurring and twinkling of astronomical objects such as stars caused by turbulent mixing in the Earth’s atmosphere varying the optical refractive index.
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Active Optics
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Active optics is a technology used with reflecting telescopes developed in the 1980s, which actively shapes a telescope’s mirrors to prevent deformation due to external influences such as wind, temperature, mechanical stress.
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Adaptive Optics
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Adaptive optics (AO) is a technology used to improve the performance of optical systems by reducing the effect of wavefront distortions: it aims at correcting the deformations of an incoming wavefront by deforming a mirror in order to compensate for the distortion.
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Radio Telescope
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an instrument used to detect radio emissions from the sky, whether from natural celestial objects or from artificial satellites.
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Star
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a fixed luminous point in the night sky that is a large, remote incandescent body like the sun
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Radiation Zone
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The radiation zone or radiative zone is a layer of a star’s interior where energy is primarily transported toward the exterior by means of radiative diffusion, rather than by convection. Energy travels through the radiation zone in the form of electromagnetic radiation as photons.
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Convection Zone
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convection zone in Science Expand. convection zone. A region of turbulent plasma between a star’s core and its visible photosphere at the surface, through which energy is transferred by convection. In the convection zone, hot plasma rises, cools as it nears the surface, and falls to be heated and rise again.
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Photosphere
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the luminous envelope of a star from which its light and heat radiate.
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Chromosphere
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a reddish gaseous layer immediately above the photosphere of the sun or another star. Together with the corona, it constitutes the star’s outer atmosphere.
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Corona
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the rarefied gaseous envelope of the sun and other stars. The sun’s corona is normally visible only during a total solar eclipse when it is seen as an irregularly shaped pearly glow surrounding the darkened disk of the moon.
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Transition Zone
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a part of the Earth’s mantle located between the lower mantle and the upper mantle. Transition zone, the region between the near and far fields of a transmitting antenna.
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Solar Wind
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the continuous flow of charged particles from the sun that permeates the solar system.
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Solar Constant
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the quantity of radiant solar energy received at the outer layer of the earth’s atmosphere that has a mean value of 1370 watts per square meter.
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Nuclear Fusion
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a nuclear reaction in which atomic nuclei of low atomic number fuse to form a heavier nucleus with the release of energy.
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Strong Nuclear Force
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The Strong Nuclear Force (also referred to as the strong force) is one of the four basic forces in nature (the others being gravity, the electromagnetic force, and the weak nuclear force). As its name implies, it is the strongest of the four.
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Proton-proton Chain Reaction
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The proton-proton chain reaction is one of several fusion reactions by which stars convert hydrogen to helium, the primary alternative being the CNO cycle. The proton-proton chain dominates in stars the size of the Sun or smaller.
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Law of Conservation of Mass
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the mass of the system must remain constant over time
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Law of Conservation of Energy
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total energy of an isolated system remains constant
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Positron
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a subatomic particle with the same mass as an electron and a numerically equal but positive charge.
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Deuteron
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the nucleus of a deuterium atom, consisting of a proton and a neutron.
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Isotope
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each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties; in particular, a radioactive form of an element.
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Neutrino
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a neutral subatomic particle with a mass close to zero and half-integral spin, rarely reacting with normal matter. Three kinds of neutrinos are known, associated with the electron, muon, and tau particle.
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Weak Nuclear Force
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The fundamental force that acts between leptons and is involved in the decay of hadrons. The weak nuclear force is responsible for nuclear beta decay (by changing the flavor of quarks) and for neutrino absorption and emission.
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Hydrostatic Equilibrium
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Hydrostatic equilibrium is the current distinguishing criterion between dwarf planets and small Solar System bodies, and has other roles in astrophysics and planetary geology.
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Granulation
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one of the small, short-lived features of the sun’s surface that in the aggregate give it a mottled appearance when viewed with a telescope.
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Sunspots
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a spot or patch appearing from time to time on the sun’s surface, appearing dark by contrast with its surroundings.
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Sunspot Cycle
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the recurring increase and decrease in the number of sunspots over a period averaging about eleven years.
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Solar Cycle
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a cycle of disturbances in the sun and its atmosphere (such as the fluctuation in the numbers and areas of sunspots or the form and shape of the corona) of an average length of about 11 years
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Prominences
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an eruption of a flamelike tongue of relatively cool, high-density gas from the solar chromosphere into the corona where it can be seen during a solar eclipse or by observing strong spectral lines in its emission spectrum.
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Coronal Holes
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a part of the solar corona that appears dark on optical and x-ray images and is characterized by low temperature and low density.
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Solar Neutrino Problems
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The solar neutrino problem was a major discrepancy between measurements of the numbers of neutrinos flowing through the Earth and theoretical models of the solar interior, lasting from the mid-1960s to about 2002.
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Parsec
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a unit of distance used in astronomy, equal to about 3.26 light years (3.086 × 1013 kilometers). One parsec corresponds to the distance at which the mean radius of the earth’s orbit subtends an angle of one second of arc.
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Star’s Proper Motion
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proper motion, in astronomy, apparent movement of a star on the celestial sphere, usually measured as seconds of arc per year; it is due both to the actual relative motions of the sun and the star through space.
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Apparent Brightness
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Apparent brightness can be defined as the number of photons per second collected at the Earth from an astronomical source. Apparent brightness depends on the light-collecting aperture of the viewing device and on the distance to the source.
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Magnitude Scale
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The moment magnitude scale (abbreviated as MMS; denoted as MW or M) is used by seismologists to measure the size of earthquakes in terms of the energy released.
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Energy Flux
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Energy flux is the rate of transfer of energy through a surface.
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Apparent Magnitude
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the magnitude of a celestial object as it is actually measured from the earth.
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Absolute Magnitude
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the magnitude (brightness) of a celestial object as it would be seen at a standard distance of 10 parsecs.
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Spectral Classes: O B A F G K M
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the group in which a star is classified according to its spectrum, especially using the Harvard classification.
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Spectral Class O
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(ionized and neutral helium, weakened hydrogen) bluish above 31,000 K
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Spectral Class B
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(neutral helium, stronger hydrogen) blue-white 9750-31,000 K
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Spectral Class A
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(strong hydrogen, ionized metals) white 7100-9750 K
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Spectral Class F
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(weaker hydrogen, ionized metals) yellowish white 5950-7100 K
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Spectral Class G
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(still weaker hydrogen, ionized and neutral metals) yellowish 5250-5950 K
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Spectral Class K
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(weak hydrogen, neutral metals) orange 3800-5250 K
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Spectral Class M
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(little or no hydrogen, neutral metals, molecules) reddish 2200-3800 K
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Radius-Luminosity Relationship
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The luminosity of a star depends upon radius and surface temperature.
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Red Giants
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a very large star of high luminosity and low surface temperature. Red giants are thought to be in a late stage of evolution when no hydrogen remains in the core to fuel nuclear fusion.
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Super Giants
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a very large star that is even brighter than a giant, often despite being relatively cool.
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H-R Diagram
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The Hertzsprung-Russell diagram, abbreviated H-R diagram or HRD, is a scatter graph of stars showing the relationship between the stars’ absolute magnitudes or luminosities versus their spectral classifications or effective temperatures.
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Main Sequence
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a series of star types to which most stars belong, represented on a Hertzsprung-Russell diagram as a continuous band extending from the upper left (hot, bright stars) to the lower right (cool, dim stars).
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White Dwarfs
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a small very dense star that is typically the size of a planet. A white dwarf is formed when a low-mass star has exhausted all its central nuclear fuel and lost its outer layers as a planetary nebula.
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Red Dwarfs
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a small, old, relatively cool star.
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Binary-Star Systems
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A binary star is a star system consisting of two stars orbiting around their common center of mass.
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Visual Binary
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a binary star of which the components are sufficiently far apart to be resolved by an optical telescope.
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Spectroscopic binary
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a binary star having components that are not sufficiently separated to be resolved by a telescope, known to be a binary only bythe variations in wavelength of emitted light that are detected by a spectroscope.
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Eclipsing Binary
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a binary star whose brightness varies periodically as the two components pass one in front of the other.
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Proxima-Centauri
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Proxima Centauri is a red dwarf about 4.24 light-years from the Sun,
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Stellar Lifetime
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The luminosity of a star is a measure of its energy output, and therefore a measure of how rapidly it is using up its fuel supply.
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Interstellar Matter
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matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space.
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Dust Grain
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Dust grains are solid, macroscopic particles composed of dielectric and refractory materials. As such, we have to deal with different and fundamentally less well-understood physics.
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Reddening Effect
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Extinction is a term used in astronomy to describe the absorption and scattering of electromagnetic radiation by dust and gas between an emitting astronomical object and the observer. Since blue light is much more strongly attenuated than red light, extinction causes objects to appear redder than expected, a phenomenon referred to as interstellar reddening
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Nebula
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a cloud of gas and dust in outer space, visible in the night sky either as an indistinct bright patch or as a dark silhouette against other luminous matter.
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21-Centimeter Radiation
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The hydrogen line, 21 centimeter line or HI line refers to the electromagnetic radiation spectral line that is created by a change in the energy state of neutral hydrogen atoms.
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Emission Nebular
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a nebula that shines with its own light.
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Dark Nebula
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a nonluminous nebula of dust and gas that is observable because it obscures light from other sources.
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Evolutionary Track
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A graphical representation of a star’s life as a path on the Hertzsprung&151;Russell diagram.
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Protostar
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a contracting mass of gas that represents an early stage in the formation of a star, before nucleosynthesis has begun.
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Zero-Age Main Sequence
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is the time when a star first joins the main sequence on the Hertzsprung-Russell diagram (HR diagram) by burning hydrogen in its core through fusion reactions.
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Brown Dwarfs
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a celestial object intermediate in size between a giant planet and a small star, believed to emit mainly infrared radiation.
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Star Cluster
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Star clusters or star clouds are groups of stars.
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Open Cluster
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a relatively loose grouping of stars.
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Globular Cluster
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a large compact spherical star cluster, typically of old stars in the outer regions of a galaxy.
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Star Formation (7 steps)
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Star formation is the process by which dense regions within molecular clouds in interstellar space, sometimes referred to as “stellar nurseries” or “star-forming regions”, collapse to form stars.
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Star Formation (Step 1)
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-Cloud collapse and fragmentation -clouds are non-uniform -densest pockets collapse first, leading to fragmentation -stars form in groups
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Star Formation (Step 2)
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-Continuing collapse of each fragment -gravitational collapse should increase Kinetic energy of cloud (motion=heat) -added heat goes into “exciting” atoms-‘radiative cooling’
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Star Formation (Step 3)
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-Fragmentation ceases, a protostar is born -central regions of the fragment become opaque to their own radiation -trapped radiation=poorer cooling -central temp is greater than surrounding gas -dense opaque inner region=protostar
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Star Formation (Step 4)
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-Protostar I -protostar continues to contract and gain mass -temp increases -pressure increases which leads to slowing in collapse -release of gravitational energy=high luminosity -equatorial plane (disc) formed (planets could form)
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Star Formation (Step 5)
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-Protostar II -contraction proceeds slowly -temperature and pressure increase
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Star Formation (Step 6)
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-Star is born -Helium production in core -nuclear reactions -radius and temp are greater than sun’s -contracts slowly as settles into equilibrium
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Star Formation (Step 7)
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-Main sequence -star reaches equilibrium -30million+ years to reach main sequence -central T=15million degrees -surface T=6000 degrees

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