Astronomy 152 Midterm Review 2023 PDF

REVIEW ASTRONOMY 152 MIDTERM Chapter 1 Light Year & Astronomical Unit (AU) are distances know relative sizes of things: moon, planet, star, solar system, local group of stars, spiral arm, MilkyWay/galaxy, clusters of galaxies, super clusters, filaments and voids Chapter 2 Constellations -stars of a...

REVIEW ASTRONOMY 152 MIDTERM Chapter 1 Light Year & Astronomical Unit (AU) are distances know relative sizes of things: moon, planet, star, solar system, local group of stars, spiral arm, MilkyWay/galaxy, clusters of galaxies, super clusters, filaments and voids Chapter 2 Constellations -stars of a constellation may be at very different distances Ancient times constellations loose grouping of stars based on mythology Now constellations are well-defined regions on the sky. Celestial Sphere – know NCP, Equator, ecliptic Altitude of Polaris = to your latitude on Earth Ecliptic – remember Sun moves 1o per day on ecliptic and highest motion +23.5o above (Summer Solstice) or -lowest, 23.5o below (Winter Solstice) Magnitude – bigger number is fainter Factor of 2.512 for each mag, (unaided eye limit ~6) Seasons – tilt of Earth’s axis – more direct sunlight in summer The Solar day is longer than the Sidereal day! Chapter 3 Moon and its Cycles Phase of Moon know Full/New/1st/3rd Waxing phases – evening; Waning phases – morning -know the time between phases.. (New moon to full moon 14 days etc.) Synodic Period - cycle of phases viewed from Earth, 29.5 days Sidereal Period – 1 orbital period around the Earth (with respect to Stars), 27.3 days Moon is Tidally Locked to the Earth– we only ever see 1 ‘face’ Eclipses: - know the conditions for an eclipse/ Nodes, Line of Nodes zone of partial shadow (grey) - Penumbra zone of full shadow (black) - Umbra. Sun & Moon both have angular diameter ≈ 0.5o Understand angular size (linear diameter/distance) Midterm Review Astronomy 152 Lunar Eclipse - only at Full Moon, can last upto 6 hrs, totality upto 100 min Solar Eclipse, only at New Moon, totality max ~7.5 min Understand what causes an annular eclipse Sun’s outer Atmosphere observed during a solar eclipse : corona & chromosphere Saros Cycle – 18yr 11.33days, but 54+ years or 3 Saros Cycles to return to same place on Earth for a solar eclipse Chapter 4 Geocentric/Heliocentric Cosmologies Geocentric – Earth is center of Universe Key Players: Plato/Aristotle/Ptolemy/Eratosthenes Epicycle - extra circle on orbit to explain retrograde motion Retrograde motion – westward (backwards) motion of a planet Parallax - angle inversely proportional to distance Heliocentric - Sun is center Copernicus/Tycho Brahe/Galileo/Kepler Kepler’s 3 laws - know these - planets move in ellipses – not circles! Revolving around the Sun with the Sun at one focus Gravity - weakest of 4 forces Galileo 1st to do experiments (heavy and light objects fall at the same rate) Velocity/Acceleration – vectors – have both a value and direction Weight/Mass - know the difference Newton’s 3 laws & Newton’s law of Universal Gravitation; force of gravity is attractive and decreases ~ 1/distance2 So twice the distance apart is ¼ of the force… Orbits - Newton explains Kepler’s 3rd law (Constant velocity, but changing direction is still an acceleration = circular orbit) & Center of Mass – balance point closest to more massive object Tides - caused by both Moon and Sun Spring (stronger tides) vs Neap (weaker tides) MidTerm Review Astronomy 152 Chapter 5: Light and Telescopes Light - part of the electromagnetic spectrum - acts as both a wave and particle Wavelength = c/frequency (c is speed of light) Energy of photon prop to frequency: E = hf Gamma-ray/X-ray - most energetic, high frequency, short wavelength IR/Radio - longer wavelength/less energetic Optical and Radio are the 2 most common wavelengths observable from the ground. Atoms are mostly empty space : Electrons orbit the nucleus of protons and neutrons: Ion – when electron(s) are removed Electrons have fixed orbits depending on their Energy – emit photons to change orbit with E = h f Telescopes : Refractors (lenses) and Reflectors (mirrors) (Refractor drawbacks - chromatic aberration, long focal length) 3 properties: LGP, Resolving power (RP), magnification Observing: Dark site, seeing, weather, water vapor Modern: thin mirrors, active optics, adaptive optics Adaptive optics help correct for the blurring of the atmosphere Kirchhoff’s radiation laws: Continuous spectrum – like a rainbow, emission at all colors Emission spectrum – bright emission lines, no or little continuous spectrum Absorption Spectrum - dark lines on continuous spectrum – like a star! Blackbody radiation : Wien’s law Lambda = 3,000,000 nm/Temperature(K) Hotter Temperature == bluer wavelength & Colder Temperature == redder wavelength Stefan-Boltzmann Law: Energy Flux ~ T x T x T x T (Kelvin = Celsius + 273) Doppler Shift – shift in wavelength caused by source motion: Red moving away, Blue toward Chapter 6 – Properties of Stars Distance to nearby stars with geometric parallax and also comparing brightness Apparent Magnitude (m) – how bright the star appears Absolute Magnitude (M) – true brightness of star as if it were at 10pc MidTerm Review Astronomy 152 Distance modulus: m – M = 5log(d/10) Stellar Spectra classes = OBAFGKM from very hot and blue to cooler and red Balmer Thermometer - Hydrogen absorption peaks at 10,000K - and every element has a characteristic best temperature for optical absorption lines. The Composition of Stars: Mostly H/He + CNO + Ca/Fe etc Spectra: The absorption lines present for a star tell you its chemical composition. The width of the lines tell you the star’s rotation The strength of the lines tell you its temperature (Balmer Thermometer) (better than from its color!) Chapter 7 – The Sun Solar Atmosphere Interior : Photosphere Core Chromosphere Radiative Zone Solar Corona Convective zone ** the Sun’s corona is very hot - what heats it is a big unsolved problem in astrophysics! Leading theories include magnetic waves or nano-flares Nuclear Fusion in the Sun’s Core – Temperature and pressure high enough to fuse H into He 4 protons combined to make 1 helium and mass is turned into energy! Solar Activity -- 22 year cycle -- currently moderate and ramping up driven by rotation and needs magnetic field. 11 years sunspot maximum to maximum, but 22 years for cycle to repeat magnetic polarity Astronomers have found spot cycles on other stars! Zeeman effect - splitting of line by B field Coronal hole – origin of Solar Wind Features: Sunspots, magnetic carpet, Spicules, Prominences, Flares Granulation – example of rising gas from convection below the surface Chapter 8 - Star Birth (& Interstellar Medium) – Types of Nebula: Emission line Nebula – Hydrogen alpha (red) emission/other elements Reflection (Blue from scattering light, like the sky) Dark Nebula (cold gas, can shroud new stars). Interstellar Extinction: gas and dust absorbs and scatters starlight; making stars appear dimmer/fainter! MidTerm Review Astronomy 152 Understand how stars are born in Giant Molecular Clouds Key points: self gravitational contraction/Conservation of Angular Momentum (MxVxR) Shocks from SuperNova and radiation from brightest stars influences and can trigger more star formation More Massive stars evolve onto Main Sequence Fastest Protostars – yet to evolve onto the main sequence. Best observed in infrared Herbig-Haro objects – young stars, have disk and jet Lets make a “Top 10 List” & Quick Questions …. Gravity - is a(n) ___________ force that varies as ______________ Kepler showed planets move in ______________ Heliocentric model – put forth by _____________ and ___________ is in the center Geocentric Model – believed by ______________ and has the ___________ at the center Retrograde motion is the apparent __________ motion of a planet on the _____________ Eclipses can only occur when the moon is ___________ and near the ________________ Daily motion of the sky; it moves from _________ to ____________ at ________ degrees per hour. Latitude vs altitude – the altitude of Polaris in the Northern hemisphere is equal to your _______ Constellations – are now considers to be _____________ An orbiting body, with constant velocity, can be accelerating, because: ____________________ From blackbody radiation __________ is a hotter color then ___red_____. You can quickly tell the temperature of a star from its _____________ The spectral sequence for stars is OBA_______ The hottest part of the Sun’s interior is the ________ and the hottest part of its atmosphere is the _________ Stars are born in _________________ and some young stars show _______ and jets. MidTerm Review Astronomy 152 *Some choices Attractive/repulsive/distance/distance squared/”1 over” distance squared/ circles/parabolas/ellipses/ Greeks/Copernicus/Galileo/lots of people/modern science/Earth/Sun/Moon Greeks/Copernicus/Galileo/lots of people/modern science/Earth/Sun/Moon Eastward/Westward/celestial equator/ecliptic New or Full/Line of Zones/Line of Nodes/Plane of Zones East to West 15 Longitude/latitude/temperature Mythological figures/regions of sky/the brightest stars It is changing its direction/it is in free fall/ it is really stationary) Blue Color FGKM Core and corona All of the molecular cloud/densest parts of a molecular cloud/galactic cetner Disks/loops/spicules MidTerm Review Astronomy 152 Sample Practice Problems 1. The Sun is near the center of our Galaxy. a. True b. False 2. Brighter Stars have larger magnitudes. a. True b. False 3. Summer is caused by the Earth being closer to the Sun a. True b. False 4. Totality last longer for a Lunar eclipse than a Solar eclipse. a. True b. False 5. Planets move faster when they are closer to the Sun. a. True b. False 6. Seen from the northern latitudes, the star Polaris a. is never above the horizon during the day. b. always sets directly in the west. c. is always above the northern horizon. d. is never visible during the winter. 7. What causes summer here in the northern hemisphere? In the summer, at this point a. the Earth is closer to the sun. b. the Earth's northern hemisphere is tilted toward the sun. c. the Earth's northern hemisphere is tilted away from the sun. 8. At the time of the summer solstice (the start of summer) the Sun is a. farthest south of the celestial equator. b. farthest north of the celestial equator. c. on the celestial equator. 9. If you were twice the Earth’s radius above the Earth, your weight would: a. increase by a factor of 2. b. decrease by a factor of 2. c. increase by a factor of 4. d. decrease by a factor of 4. e. stay the same.. MidTerm Review Astronomy 152 KEY 1. B 2. B 3. B 4. A 5. A 6. C 7. B 8. B 9. D MidTerm Review Astronomy 152  Notes & Organization Review Lecture notes, re-read sections of the book on tricky concepts. Sketch the pictures, take more notes, and organize your thoughts. Important Topics Most important concepts Constellations Solar Day vs Sidereal Day Celestial Sphere How the Sky Works Seasons Scale of things Magnitudes Cycle of the Moon Eclipses Geocentric model Heliocentric Model Kepler’s Laws Newton’s Laws/Gravity Orbits Tides Black body and Kirchhoff’s laws -Blue is hotter than red! Star’s Spectral Sequence OBAFGKM/HR Diagram Properties of our Sun Star Birth What I am confident in What I need to re-read/review MidTerm Review Astronomy 152