Astronomy 113- 002
Astronomy 113- 002 astronomy 113
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This 5 page Class Notes was uploaded by Morgan Owens on Friday January 22, 2016. The Class Notes belongs to astronomy 113 at George Mason University taught by Pesce in Winter 2016. Since its upload, it has received 191 views.
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Date Created: 01/22/16
Introduction: Astronomy & astrophysics Astron = star Nomos= law Physic= nature Astronomy: observable properties of objects in the sky ex: brightness, motion Astrophysics: Intrinsic properties of objects ex: mass Our understanding is based in the laws of physics electro magnetic, gravity, & quantum mechanics Key facts about info in astronomy: scientific method, hypothesis, no proof answer is correct there is just supporting evidence no definitive answers universe is every changing wonderful and violent celestial objects evolve stars are born and die, universe expands Astronomy in a time machine everything we observe we observe in the past, more distant= more distant in past. Ex: Takes 8 minutes for sunlight to reach our skin an indirect science Assumptions: We must assume laws of physics are valid everywhere (space and time) It’s a branch of physics Modern astronomers try to determine physical nature of celestial objects and relationship among the various objects Philosophical Replacement of geocentric cosmology with heliocentric one different between modern philosophy, religion, culture and music Publicity modern technology arises from understanding laws of nature (basic science) * less rapid development if all scientist were involved in Applied Science Astronomy in everyday life: IPhone has nice camera, chip measures light and lots and lots of pixels which is how the camera takes a photo, if it weren’t for astronomers there wouldn’t be the CCD cameras that are in your phone. Direct application of astronomy into lifestyle Astronomy is observational rather than experimental, all direct information about conditions of celestial objects must come from an understanding of the nature of atoms and the constituents. Everything is based on the Scientific Method theory must be consistent with observations, theory then enables us to make predictions which can be test and then tweak hypothesis. (Observe, theorize, and test) Cycle definition: 1. Create hypothesis 2. Prediction 3. Observation info gathering 4. Hypothesis testing –intent is to disprove hypothesis Usually cycle is like this *But we can very much be influenced by the confirmation bias 1. Initial observation (Need to explain something, ask “what is that?”) 2. Create hypothesis 3. Prediction 4. Observation 5. Hypothesis testing Scientific Notation 10 followed by an exponent or superscript = # of zeros Why Scientific Notation? Scales! Numbers are vast, humans make scales such as inches, meters. Numbers in astronomy quickly become unimaginably large Astronomical unit (AU) average distance between the Earth and the sun. which equals 1.5x10^8 (93 million miles) “light year” distance (measure of distance) light travels in 1 year 186,000 miles per second. So in 1 year light travels 63,000 AU Parsec (PARallax SECond) the distance at which 1 AU makes an angle of 1/3600 degree. 1 pc= 3.09 x 10^13 km Proxima Centauri 1 kpc = kilo pc distance from the sun to center of Milky Way 1 Mpc = Mega pc distance to the nearly cluster of galaxies Size Scale Earth – 10^3 km Solar system 10^810 Stars – 10^1315 Galaxy 10^18km Time: Remember that light travels at a fast but finite speed It takes time for light to travel between objects (light year = distance light travels in 1 year) Astronomical time machine: Moon – 1.5 seconds Sun – 8.5 minutes Pluto – 45 hours Center of galaxy 25,000 years ago Scales: It would take you 80 years to count to 1 Billion years if you started when you were born. The universe is 400 Million Billion seconds old. Size/Distance examples: Object Radius Sun 7 x 10^10 cm Earth 6 x 10^8 cm Moon 2 x 10^8 cm If the sun is 1 meter in diameter Earth would be 1 centimeter (Marble) Moon would be .3 centimeter (BB) Jupiter would be 4 inches At this scale 1 AU would = 214 meters Proxima Centauri would = 35,700 miles Early Views: Early centuries had advanced ides and the Greeks wanted to understand nature. Aristarchus (300 BC) proposed the sun was the center model because he knew the sun was distant. Also contributes the moon diameter compared to the Earth and the distance of the moon to the sun. All was based on observation rd Eratosthenes (3 Century BC) Measured diameter of the Earth by used its shadow and discovered that the Earth was round. Hipparchus: Observed stars and compared catalogs Greeks were stuck in thinking everything was perfect in nature Ptolemy (130 AD) Makes star chars and brightness systems but still believed the Earth was the center of the universe. Greeks observed motions of planets with respect to background stars. Epicycles: Made models of planets with the earth being center Nicholas Copernicus: Still stuck in the idea that nature was perfect and unchanging. Discovered that as planets were closer to the sun their orbit was faster and their years were shorter ( but still stuck in the idea of perfect circular orbit) Heliocentric isn’t more accurate that geocentric models but just simpler. Occam’s razor: helps to choose between two ideas, states that you should follow the simpler idea. Supernova 1572: Caused questioning that the heavens weren’t unchanging (Greeks idea) Those trying to figure out what it was couldn’t detect a parallax which indicated that it was far away. 1600: Kepler abandons the idea of perfect circular orbit motion or elliptical orbit Kepler’s 3 Laws: 1. Orbit is ellipse – sun is the center 2. Law of equal areas 3. Closer to the sun = more rapid a planets orbit and shorter year. Galileo (1610) st 1 person to point telescope at night sky. Discovered phases of Venus – using a heliocentric system Found 4 large moons of Jupiter which follow Kepler’s laws Sunspots imperfections All support heliocentric and changing universe but his physics was a problem Isaac Newton 1660s: Law of inertia force acting on planets Velocity Acceleration Force = mass x acceleration Momentum Gravity universe las Proof of Heliocentric Model: Aberration of light Parallax Rotation of the Earth Nature of Light: White light = all colors Prisms separate light Speed of light = finite but fast Waving electric and magnetic fields Color = different wave lengths light is sometime a wave or particle shorter wave = higher energy visible light is only a small component of EM radiation ROY G. BIV – Red, Orange, Yellow, Green, Blue, Indigo, Violet Waves: Large waves short waves Radio Infrared visible – ultra violet X rays – y rays Not all are transmitting by atmosphere
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