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ASTRO 120 - Final Exam Review

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Gregory Sivakoff

ASTRO 120 FINAL REVIEW CHAPTER 1 CHAPTER 2 - North celestial pole – the point directly over Earth’s North Pole - South celestial pole – the point directly over Earth’s South Pole - Celestial equator – projection of Earth’s equator; complete circle around celestial sphere - Ecliptic – the path the sun follows as it appears to circle around the celestial sphere - Local sky – the sky as seen from wherever you happen to be standing - Horizon – boundary between the Earth and the sky - Zenith – the point directly overhead - Meridian – imaginary half circle stretching from N to S through the zenith - Position of any object in the sky: o Direction (N, E, S, W) o Altitude (in degrees) - Angular size of an object is the angle it appears to span in your field of view - Angular distance is the angle that appears to separate two items in the sky o 360 degrees in a full circle o 1 degree = 60 arcminutes o 1 arcminute = 60 arcseconds - Zodiac – constellations along the ecliptic - Solstices and equinoxes: o Summer solstice: June 21 [light rays most intense] o Fall equinox: September 22 [light rays medium intense] o Winter solstice: December 21 [light rays least intense] o Spring equinox: March 21 [light rays medium intense] - Precession – gradual wobble that alters the orientation of Earth’s axis in space - Lunar phases: New Waxing First Waxing Full Waning Third Waning Moon Crescent Quarter Gibbous Moon Gibbous Quarter Crescent Rise 6:00 9:00 Noon 15:00 18:00 21:00 Midnight 3:00 Highest Noon 15:00 18:00 21:00 Midnight 3:00 6:00 9:00 Set 18:00 21:00 Midnight 3:00 6:00 9:00 Noon 15:00 - Saros cycle – the sun, the earth and moon are in the same relative geometry and a nearly identical eclipse occurs every 18 years 11.3 days - Apparent retrograde motion (retrograde = backward) - Stellar parallax: CHAPTER 3 - Ptolemaic model – accounted for apparent retrograde motion - Copernican revolution – spurred the development of virtually all modern science and technology - Ellipse: - Kepler’s First Law – the orbit of each planet is an ellipse with the Sun at one focus o Perihelion is the closest point (b) o Aphelion is the farthest point (a) - Kepler’s Second Law – as a planet moves around its orbit, it sweeps out equal areas in equal times - Kepler’s Third Law – more distant planets orbit the Sun at slower average speeds 2 3 o p =a - e=c/a o perihelion distance = a(1-e) o aphelion distance = a(1+e) - Galileo solidified the Copernican revolution by explaining how the phases of Venus would only range from New to Crescent if it followed the Ptolemaic model, but since we see all the phases ranging from New to Full, we can deduce that the Copernican model is correct, heliocentric. CHAPTER S1 - Days o Sidereal day – 23 hours 56 minutes – “related to the stars” – precise rotation period o Solar day – 24 hours – “related to the sun”  4 minute difference because the Earth needs to rotate 361 degrees to face the sun - Months o Synodic month – 29.5 days – when the Sun and the Moon “meet” in the sky – New Moon o Sidereal month – 27.3 days – “related to the stars” – precise rotation period - Years o Sidereal year – “related to the stars” o Tropical year – ~20 minutes shorter than the sidereal year, focuses on seasons - Periods o Sidereal period – the time the planet takes to orbit the sun “related to the stars” o Synodic period – when the planet is lined up with the sun in our sky at one time and the next similar alignment CHAPTER 4 - Momentum = mass x velocity - The only way to change an object’s momentum is to apply a force to it - Angular momentum = mass x velocity x radius - The only way to change an object’s angular momentum is to apply a torque to it (twisting force) Newton’s Law of Motion - Newton’s First Law – An object moves at constant velocity if no net force is acting on it - Newton’s Second Law – Force = mass x acceleration - Newton’s Third Law – For any force, there is always an equal and opposite reaction force Conservation of Momentum – mv+mv=mv+mv Conservation of Angular Momentum – mvr+mvr=mvr+mvr Energy: - Kinetic energy – energy of motion - Radiative energy – energy carried by light - Potential energy – stored energy Inverse square law of gravitation: Newton’s version of Kepler’s Third Law: CHAPTER 5 - 1 watt = 1 joule/s - How do light and matter interact? o Emission o Absorption o Transmission o Reflection/scattering - Wavelength x Frequency = Speed - Wavelength = 1/Frequency - Frequency = Hz (cycles per second) - Electromagnetic spectrum Atoms - Atomic number – number of protons - Atomic mass number – number of protons plus neutrons o Different atomic mass numbers of the same element are called isotopes Spectrums - Continuous spectrum - Emission line spectrum – cloud of gas emits light only at specific wavelengths - Absorption line spectrum – cloud of gas absorbs light only at specific wavelengths - Thermal radiation (known as blackbody ratdiation) produced a thermal radiation spectrum o Most common type of continuous spectra o More Energy – More Temperature – Smaller average wavelength of light given off CHAPTER 6 Telescopes - Light-collecting area – how much total light the telescope can collect at one time o Because area is proportional to the square of a telescope’s diameter, a 10-meter telescope has 5 times the diameter of a 2-meter telescope, but it’s light-collecting area is 5x5=25 times as great - Angular resolution – the smallest angle over which we can tell that two dots, or two stars, are distinct o Human eye’s angular resolution of an eye is 1 arcminute - Diffraction limit depends on both the diameter of the telescope and the wavelength of light being observed o Larger telescope = Smaller diffraction limit o Longer wavelength of light = Larger diffraction limit - Light pollution – lessens the quality of observations - Atmospheric turbulence – stars twinkle, blurring their images - Adaptive optics – technologies can overcome some
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