Astronomy Exam 2 PDF

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Exam 2 Study Sheet for Astronomy 114 Christopher Taylor...

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Structure of the sun: Corona, Convection Zone Radiation Zone, Core. Core is where nuclear fusion takes place.Luminosity—total energy radiated by the Sun— can be calculated from the fraction of that energy that reaches Earth. Solar constant—amount of Sun's energy reaching Earth—is 1400 W/m2. Total luminosity is about 4 × 1026 W—the equivalent of 10 billion 1-megaton nuclear bombs per second. Physical Properties of the Sun Radius—6.9x108m (109 x Earth) Mass—1.99x1030kg (300,000 Earths). Sun is stable because weight of upper layers compresses lower layers. Mathematical models, consistent with observation and physical principles, provide information about the Sun’s interior In equilibrium, inward gravitational force must be balanced by outward pressure. Energy Balance:The rate at which energy radiates from the surface of the Sun must be the same as the rate at which it is released by fusion in the core. Solar wind: A flow of charged particles from the surface of the Sun. Corona:Outermost layer of solar atmosphere 5500 celsius. Chromosphere:Middle layer of solar atmosphere. Photosphere:Visible surface of Sun.Convection Zone:Energy transported upward by rising hot gas. Radiation Zone:Energy transported upward by photons. Core:Energy generated by nuclear fusion. Why does the Sun shine? The Sun shines because gravitational equilibrium keeps its core hot and dense enough to release energy through nuclear fusion. Fission: Big nucleus splits into smaller pieces. (Example: nuclear power plants). Fusion: Small nuclei stick together to make a bigger one.(Example: the Sun, stars).High temperatures enable nuclear fusion to happen in the core.The Sun releases energy by fusing four hydrogen nuclei into one helium nucleus.Energy transport: The radiation zone is relatively transparent; the cooler convection zone is opaque. Random Photon Walk:Energy gradually leaks out of radiation zone in form of randomly bouncing photons.Convection (rising hot gas)-takes energy to surface. Determine the peak wavelength of light radiating from the Photosphere(2.9*10^-3/T(Kelvin)). Sunspots-Are cooler than other parts of the Sun's surface. Zeeman Effect We can measure magnetic fields in sunspots by observing the splitting of spectral lines. Magnetic activity causes solar flares that send bursts of X rays and charged particles into space. Magnetic activity also causes solar prominences that erupt high above the Sun's surface.Parallax is the apparent shift in position of a nearby object against a background of more distant objects.Parallax angle depends on distance. D = 1/p. d= 3.26*1/p. Barnard’s star has the largest proper motion of any star proper motion is the actual shift of the star in the sky, after correcting for parallax.Doppler shif tells us ONLY about the part of an object's motion toward or away from us. Apparent brightness:Amount of starlight that reaches Earth (energy per second per square meter). Magnitude scale, lower the number, the brighter the star is. Apparent Magnitude-Brightness measured at actual distance from the Earth. Absolute Magnitude-Brightness measured at 10 parsecs from the Earth. The orbit of a binary star system depends on strength of gravity. Types of Binary Star Systems: Visual binary- Both stars can be seen directly, and their separation and relative motion can be followed directly Spectroscopic binary-We determine the orbit by measuring Doppler shifts. Spectroscopic binaries can be measured using their Doppler shifts Eclipsing binary- thingy makes an ellipse. Thermal Radiation-Nearly all large or dense objects emit thermal radiation, including stars, planets, you. An object's thermal radiation spectrum depends on only one property: its temperature. Properties of Thermal Radiation -1. Hotter objects emit more light at all frequencies per unit area. 2. Hotter objects emit photons with a higher average energy. The color of a star is indicative of its temperature. Red stars are relatively cool, whereas blue ones are hotter. (Hottest)OBAFGKM(coolest). An H-R diagram plots the luminosity or Absolute Magnitude as a function of temperature or spectral type of stars.

The M-K System. 1-supergiant.2-bright giant.3-giant.4-subgiant.5.main sequence. 6.Sub dwarfs. 7.White Dwarfs. Examples: Sun - G2 V Sirius - A1 V Proxima Centauri - M5.5 V Betelgeuse - M2 I. Main-sequence stars are fusing hydrogen into helium in their cores like the Sun. Luminous mainsequence stars are hot (blue). Less luminous ones are cooler (yellow or red).Mass measurements of mainsequence stars show that the hot, blue stars are much more massive than the cool, red ones. The mass of a normal, hydrogenburning star determines its luminosity and spectral type. Trends in the HR Diagram: Mass increases from bottom right to top left, size increases from bottom left to top right. Luminosity: from brightness and distance 10–4LSun–106LSun.Temperature: from color and spectral type 3000 K–50,000 K Mass: from period (p) and average separation (a) of binary star orbit 0.08MSun – 100MSun Radius: from Steffan-Boltzman’s Law 0.0001RSun – 1000RSun. Spectroscopic parallax: Has nothing to do with parallax, but does use spectroscopy in finding the distance to a star. 1. Measure the star’s apparent magnitude and spectral class 2. Use spectral class to estimate luminosity 3. Apply inverse-square law to find distanceThe spectroscopic parallax calculation can be misleading if the star is not on the main sequence. The width of spectral lines can be used to define luminosity classes....