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ASTR 100

ASTRONOMY MIDTERM 1 STUDY GUIDE 1. Lecture 1 a. Basic Philosophy and the Scientific Method i. Scientists look for the best model 1. Best model may not be 100% accurate a. Scientists try not to confuse models with the truth 2. Usually models are formed from a theory that is eventually gets tested a. Models are very efficient 3. Based on observations a. Examples include: Isaac Newton’s theory of gravity andAlbert Einstein’s theory on relativity b. Distances inAstronomy i. Astronomical Unit (AU) 1. Distance between Earth and Sun 2. 93 million miles 3. 8.3 light minutes 4. 149,597,871 kilometers ii. Light year (LY) 1. 9.4605284 × 10 meters 2. 5.87849981 × 10 miles iii. 1 Parsec = 206,265AU = 3.26 LY (PC) 2. Lecture 2 a. Celestial Sphere i. zenith / nadir 1. Zenith is the highest point in the sky usually right above you 2. Nadir is the point directly below a certain location ii. Meridian 1. The line through the sky that runs through the north point through the zenith to the south point iii. celestial poles 1. The pole of the Earth projected straight the celestial sphere 2. Polaris closest Star to the northern celestial pole 3. Cannot see south celestial pole from Champaign iv. circumpolar stars 1. stars that seem to circle the pole 2. never rise and never set 3. Based on where you are on Earth the stars that are circumpolar can change a. Based on Latitudinal position v. Altitude of celestial pole = latitude 1. 40 degrees in latitude means 40 degrees up on the celestial pole is where you will find the north star 2. Champaign is at the 40 degrees in latitude vi. Motions of stars 1. At equator a. Perpendicular to the horizon 2. At north/south pole a. Parallel to horizon vii. Ecliptic = Zodiac 1. Zodiac constellations rest on the ecliptic viii. Seasonal Motion of Stars 1. 4 minute change per day 2. Sun moves along ecliptic as well and will block our view of some stars depending on where it is positioned on the celestial sphere 3. 1 degree away from the sun is 4 minutes after the sun 3. Lecture 3 a. Seasons: Outside View i. The Earth is tilted so as it goes around the sun it tilts generally in the same direction for the entire year ii. The sun is seen against zodiacal constellations b. Axial tilt 23 1/2 degrees i. Pole fixed in space c. Seasons: Inside view i. Sun is seen in zodiacal constellations d. Sun "moves" along zodiac on the ecliptic e. Twice per year on celestial equator i. When this happens day is equal day and night ii. Solstice = path of the sun is either 23.5 degrees above or below the celestial equator f. key dates i. Vernal Equinox (March 20-21) ii. Summer Solstice (June 21) 1. Sun rises to the north of the celestial pole iii. Autumnal Equinox (Sept 23) iv. Winter Solstice (Dec 22) 1. Sun rises to south of the east point g. Cause of Seasons: i. Earth’s tilt and rotation around sun 1. Length of day changes a. 10 hrs. in winter b. 14 hours in summer in Champaign 2. Projected energy (direction) of sunlight a. Winter day sun comes in on an angle and sunlight spread over wide area b. summer day the sun is high in the sky and same amount of energy and sunlight hits small area h. Precession: i. Discovered my Hipparchus in 140 BC ii. Constellations were first defined in 3000 BC when pole star was Thuban iii. Earth has a bulge 1. Diameter bigger around equator than on sides iv. Sun tries to pull the Earth back up v. When the top wiggles it is precessing vi. Pole of earth move around in a circle that takes 26,000 yrs. to complete i. Lengths of the Year i. Sidereal year 365.25 ii. Civil year 365, 366 j. Names of the Months i. March ii. April iii. May iv. June v. July vi. August vii. October viii. November ix. December x. January xi. February 4. Lecture 4 a. Moon i. Periods: sidereal & synodic 1. Sidereal 27.3 days a. Relative to the stars the amount of time the moon takes to go around in a full circle 2. Synodic 29.5 earth days a. One full moon to the next full moon 3. These are different because the earth moves around the sun, so for the moon to get back to full it must take a few extra days to return to the exact same spot when viewed from Earth b. Orbital plane tilted 5 degrees c. Phases i. New-first quarter-full-third quarter 1. Takes 7 days to get to each new phase ii. Waxing getting bigger iii. Waning- getting smaller iv. Gibbous and crescent are the in-between phases d. Eclipses i. Umbra = darkest region (of shadow) ii. Penumbra= half dark and half light iii. Lunar eclipse- 1. Full moon gets dark a. Moon gets in earths shadow iv. Solar Eclipse 1. Sun is blocked by new moon a. Lasts an average of 2 minutes b. Longest 7 minutes v. Annular Eclipse 1. New moon does not block the sun completely a. Leaves bright outer ring vi. Eclipses do not happen every full or new moon very narrow band of where it could occur e. Chromosphere & corona i. The chromosphere (literally, "sphere of color") is the second of the three main layers in the Sun's atmosphere and is roughly 2,000 kilometers deep. It sits just above the photosphere and just below the solar transition region. 1. Can only be seen during total eclipse otherwise invisible ii. Acorona (Latin, 'crown') is a type of plasma that surrounds the Sun and other celestial bodies, including the Earth. The Sun's corona extends millions of kilometres into space and is most easily seen during a total solar eclipse, though it is also observable in a coronagraph. The word "corona" itself derived from the Latin, meaning crown, which in turn came from theAncient Greek κορώνη (korōnē) meaning "garland" or "wreath". f. Prominences g. Diamond ring effect i. As moon reveals part of sun after eclipse looks like diamond ring h. Dates of Occurrence 5. Lecture 5 a. Greek astronomers: i. Aristotle (350 BC), 1. Earth is round 2. 4 basic elements:Air, water, Earth, Fire 3. Said Earth was fixed at center of universe 4. Said the stars in the heavens never changed 5. Celestial sphere is crystalline a. Stars are little lights on the sphere 6. Views were adopted as the truth by Holy Roman Empire ii. Hipparchus (140 BC) 1. Cataloged stars a. Made first atlas and estimated the brightness of the stars b. Named stars by their position in mythological descriptions c. Described brightness of magnitude 1-6 i. 1= brightest stars 2. Discovered precession 3. Predicted ellipses 4. Used parallax to determine the distance to the moon a. Parallax- the relative motion of a foreground object relative to a more distant fixed object 5. Retrograde motion- at times when planets will sometimes reverse their motions east to west a. Earth is passing the planet or star making it appear that the object in the sky is going backwards 6. Prograde motion- west to east iii. Ptolemy (140AD) 1. Worked at library inAlexandria 2. Used Hipparchus star catalog 3. Wrote theAlmagest that predicted the sun, the moon, and the planets positions for more than 1000 years 4. Earth centered cosmology with epicycles a. Epicycles- small little orbits inside big orbit iv. Copernicus (1543) 1. Renaissance scholar traveled throughout Europe 2. First to propose and support with observation the heliocentric theory a. The earth isn’t the center of the solar system the sun is b. Was able to look how close planets were to the sun and was able to propose orbits of the planets using geometry 3. Thought orbits were circular not ellipses 4. Published book “De Revolutionsibus” while he was dying v. Tycho Brahe (1600) 1. Great observer a. Determined accurate positions of stars and planets th in skies within 2 arc minutes (1/15 diameter of moon) i. Observed from island of Hven b. Used an instrument using two sticks and measuring angle between them c. Saw no parallax for a comet and a nova i. Nova=new star d. Hired kepler as assistant 2. Model of the universe: Earth at center 6. Lecture 6 a. Kepler (1610) and Kepler's Laws i. 3 laws 1. Orbits of planets are ellipses a. Sun is at one foci b. As eccentricity approaches 0 get closer to being a circle 2. Planets sweep out equal area in equal time a. Perihelion- where planet is closest to sun b. Aphelion- planet furthest from sun 3. Period squared= (radius of the orbit) distance^3 a. P^2=area^3 i. Period in years radius inAU ii. First to show that images formed by eye are projected upside down b. Galileo (1610) i. Wrote book called Starry Messenger ii. Conducted physics experiments 1. Leaning tower of Pisa experiment 2. Studied friction of sliding objects 3. Understood path of cannon balls (parabolic motion) iii. Built telescopes and observed the heavens 1. Discoveries a. Mountains. Craters, and Maria on moon b. Sunspots on the sun c. Phases and changing diameter of Venus i. Helped prove that Earth was not the center of universe d. Moons of Jupiter and their motion i. Helped prove earth was not center of the universe e. Milky way consists of crowded star fields 7. Lecture 7 a. Isaac Newton (1666) b. Studied nature of light, motion, optics, astronomy, tides i. First to understand tides ii. Invented calculus 1. Invented calc, universal laws of motion and gravitation put into place by Newton in 1666 iii. Made first reflecting telescope c. Studied alchemy & religious history d. Member of Parliament & Master of the Mint i. Re-minted gold and silver coins to make edges serrated e. Laws of Motion i. First law 1. Objects at rest remain at rest and objects in motion remain in motion until acted upon by and external force (inertia) ii. 2 law 1. force= mass*acceleration iii. Third Law 1. For every force there is an equal and opposite force f. mass, velocity, acceleration, force, work, momentum i. if you give an object no energy it moves in a circle, give some energy it moves in an ellipse g. Law of Universal Gravitation i. F=G*M1*M2/distance^2 h. Orbit of Moon i. Falls towards earth i. Tidal Force j. Satellites k. Circular velocity i. V=squareroot(GM/r) ii. Orbital velocity iii. Earth’s 28400 k/hr l. Velocity of escape i. V=squareroot(2GM/r) ii. Isaac Newton is famous for discovering the idea of Universal Gravitation 8. Lecture 8 Electromagnetic Radiation a. Basic Properties i. waves are transverse like a sin curve 1. energy runs perpendicular to the direction of motion ii. act like particles and waves iii. speed is constant b. Wavelength x frequency = c c. c = Speed of light 3.0*10^8 d. Waves are transverse (not longitudinal) e. Energy = constant x frequency f. Properties: wave and particle g. Electro-Magnetic Spectrum h. Gamma Rays, X-rays, UV, visible, infrared, microwave, radio i. Violet-blue-green-yellow-orange-red ii. High frequency to low frequency iii. Small wavelength to long wavelength i. How radio antennas work i. Copper wire at top of tower 1. Little building next to it oscillates the copper at a certain frequency j. Refracting and Reflecting Telescopes i. Refracting telescopes use lenses ii. Reflecting telescopes use mirrors k. How lenses work (and fail) i. Lenses slow down the light and bend it 1. Then brings light to a focal point l. How mirrors focus light 9. Lecture 9 Telescopes and Optics a. Telescopes Overview i. Lens that lets light in is called objective lens ii. Eyepiece is used as magnifying lens to see image created on the focal point iii. Chromatic effect- color effect iv. Reflecting 1. No chromatic effect 2. Concave mirror a. Make surface a parabola b. Prime focus- main focus of a mirror c. Four different types of foucs i. Newtonian focus 1. Flat secondary mirror 2. Then focal point at side ii. Cassegrain focus 1. Curved secondary mirror 2. Then focal point down through primary mirror iii. Nasmyth focus and coude mirror 1. Curved secondary mirror 2. Newtonian mirror 3. Focal point out to the side b. Lenses Refract: smoothness, focal length, color effects c. Mirrors Reflect d. Telescopes in Astronomy e. Collect light, resolve, magnify f. Refracting Telescopes inAstronomy: Yerkes i. Galilieo g. Reflecting Telescopes inAstronomy h. World's Largest Telescopes are reflectors: Keck, VLT i. Active and adaptive optics i. Active optics- to adjust a big mirror once every minute or so to maintain its physical shape ii. Adpaptive optics 1. Adjust a small mirror up to 2,000 times per second to cancel blurring effects of the Earth’s atmosphere j. New Giant Telescopes k. Instruments for Telescopes i. Cameras 1. Sensitive to specific wavelengths a. UV, visible, infrared 2. Spectropgraphs a. To measure Doppler shifts of galaxies b. To study conditions in stars and nebulae c. To watch stars velocities wobble very small amounts l. Eye, Film and CCDs 10. Lecture 10 a. Eye, Film and CCDs: images i. CCD 1. Charge Coupled Device a. Made of wafer silicon with ion impants to define pixels b. Pixels= picture elements c. Developed in the 1980s by engineers and
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