Discover the Universe Week 2
Discover the Universe Week 2 AST 1002
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This 9 page Class Notes was uploaded by Jocelyn on Monday September 7, 2015. The Class Notes belongs to AST 1002 at University of Florida taught by Reyes, Francisco J in Summer 2015. Since its upload, it has received 119 views. For similar materials see Discover the Universe in Science at University of Florida.
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I was sick all last week and these notes were exactly what I needed to get caught up. Cheers!
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Date Created: 09/07/15
Tuesday September 1 2015 Discover the Universe Week 2 Ch 0 Charting the Heavens Continued Reminder Earth precesses like a top but very slowly Precession of the Equinoxes Cont d Tropical year The amount of time between one equinox to another which corresponds to 365242 solar days Sidereal year The amount of time it takes for the Earth to orbit the sun The reason for the disparity between the two types of years is caused by precession The year represented in our calendars is the tropical year The Moon Why do we see faces The moon actually doesn t project its own light by reflecting light from the Sun it shines The half of the moon that is facing the sun will always be illuminated During a new moon only the dark side of the moon is visible During a full moon only the illuminated half is visible Rising and Setting times of the moon During a new moon the moon rises at sunrise and sets at sunset During a full moon the moon rises at sunset and sets at sunrise Lunar Phases The complete cycle from new moon to the next new moon takes about 29 days The age of the moon is the number of days since new moon Synchronous rotation the moon rotates on its axis in exactly the same time it takes to orbit the Earth Sidereal and Synodic Month Sidereal month The amount of time it takes for the moon to complete one revolution with respect to a reference star A sidereal month lasts 273 days Synodic month The amount of time for the Moon to complete a full cycle of phases AKA new moon to new moon Instead of a star as a reference the Sun is the reference point Synodic month lasts 295 days Tuesday September 1 2015 Lunar Eclipse 0 A lunar eclipse occurs when the Earth blocks the Sun s light from reaching the Moon 0 The Sun and the Moon MUST be in opposite directions as seen from Earth 0 The phase of the Moon MUST be Full Moon 39 Visible anywhere on Earth where the Moon is visible The red coloration is caused by sunlight deflected by the Earth s atmosphere onto the Earth s surface Solar Eclipse A solar eclipse occurs the Moon blocks the Sun s light from Earth REMEMBER the Sun and the Moon have the same angular size 05 The phase of the Moon MUST be New Moon Only visible in m locations on Earth 3 Types Total Partial and Annular Total Solar Eclipse Occurs during perfect alignment and allows planets and stars to become visible during the daytime since the Sun s light is blocked We can see the Sun s corona the Sun s outer atmosphere Partial Solar Eclipse the Moon s path is slightly off center and only a potion if the Sun s face is covered Why are some solar eclipses annular The elliptical orbit of the Moon When the moon is farthest away from the Earth Apogee away When the moon is closest to Earth Perigee Thursday September 3 2015 Why don t we see eclipses every month The Moon s orbital plane is tilted 5 degrees to the ecliptic the plane in which Earth crosses the Sun 0 Since the Moon s orbit is slightly inclined to the plane of the ecliptic we don t see a lunar eclipse at each full moon Parallax and stellar parallax Parallax the displacement of the foreground object respect to the background as the observer s location changes Stellar Parallax When a nearby object changes position with respect to the star background as though it is viewed by two sites separated by a terrestrial diameter The amount of parallax is inversely proportional to an object s distance Science and the Scientific Method Theory is a framework of ideas to explain observations that also make predications about a phenomenon It must be testable Thursday September 3 2015 Chapter 1 The Copernican Revolution The Sun Moon and the stars move across the sky smoothly with changes only occurring very slowly However in early times observers noticed that five other bodies known as planets moved in a different fashion Planets were known to wander across the celestial sphere in 2 different ways Direct Motion regular eastward movement across the sky Retrograde Motion backward westward motion Planet is brighter when in retrograde motion due to its distance from Eanh The Geocentric Models Followed teachings of Aristotle 1 Geocentric Model EARTH is at the center of the universe with planets and Sun orbiting IT in circular orbits Explained planetary motions using deferents and epicycles 2 Ptolemaic Universe Useful at the time although later wrong for predicting the position of the first five recognized planets Mercury Venus Mars Jupiter and Saturn Survived almost 13 centuries from 140 BC to 1500 BC Nicholas Copernicus Rediscovered the idea of a heliocentric model by Aristarchus This model predicted the idea that all planets revolve around the SUN Since Aristotle s influence was too strong Aristarchus ideas didn t gain much recognition Copernicus introduced the Mathematical model for a heliocentric universe Copernican Revolution is known as the realization that the Earth is not at the center of the universe Thursday September 3 2015 Why were his ideas not widely accepted 1 Conventional wisdom believed that the Earth was at the center of the universe 2 It violated the religious Doctrine of the Catholic Church 3 It wasn t much better than the geocentric model in terms of predicting positions 4 No observational evidence available 5 Example If the Earth revolves around the Sun why don t we see stellar parallax In the heliocentric system the retrograde motion of the planet is naturally explained When the Earth approaches and overtakes a planet in orbit a planet APPEARS to undergo retrograde motion The Birth of Modern Astronomy Galileo Galilei 15641642 Father of experimental science First to point a telescope that he built himself at the sky in 1609 Discoveries include 1 Moon craters mountains and valleys 2 Dark spots known as Sunspots and the Sun s rotation since the spots drifted across the disk once per month 3 Moons of Jupiter known as satellites lo Europa Ganymede and Callisto 4 The Planet Venus and its phases new Venus to full Venus Refracting telescope is also known known as the Galileo telescope With the geocentric model the phases of Venus had no explanation but in the heliocentric model it was simple to explain the full phase of Venus Galileo s observations contradicted the geocentric model because 1 Venus orbits the Sun rather than Earth N Jupiter s satellites orbit Jupiter rather than Earth 03 They challenged the scientific orthodoxy and religious dogma Thursday September 3 2015 Laws of Planetary Motion Tycho Brahe 1546 1601 Built large instruments with large circles to observe planet s positions with accuracy although they had no optics Recorded impressive nakedeye positions of planets Employer of Kepler who inherited all of his data upon death Johannes Kepler 15711630 Goal was to find within the framework of the Copernican model a way to include Tycho Brahe s data This way he could describe the shapes relative to the size of planetary orbits He struggled to fit the data in the Copernican heliocentric model with Circular orbits To incorporate the data the planets had to be assumed to have Elliptical orbits His three laws of planetary motions are empirical Kepler s First Law The orbital path of the planets are elliptical with the Sun at one focus Perihelion shortest distance from the Sun Aphelion largest distance from the Sun Eccentricity of an ellipse Eccentricity Major Axis Minor Axis Major Axis c distance from center to focus a semimajor axis eccentricity ca Thursday September 3 2015 Kepler s Second Law An imaginary line connecting the Sun and any planets sweeps out equal areas of the ellipse in equal intervals of time As a result from applying the second law the planets move fastest at perihelion and slowest as aphelion area A area B area C Kepler s Third Law The square of a planet s orbital period is proportional to the cube of its semimajor axis PA2 aA3 gt P Period 2 a semi major axisquot3 P Period in years time for one orbit a Semimajor axis in AU The larger the distance between the planet and the Sun the longer the period of the planet PA2 aquot3 1 Example Orbital Period P 1 year Distance a to the Sun 2 1 AU What is the orbital period or the year of a planet located at a distance of 10 AU from the sun Should the period be 10 years PA2 103 PA2 1000 P Square root of 1000 P 315 years Thursday September 3 2015 Recap Kepler s Laws tell us the shape of each planet s orbital motion the period and relative distance to the Sun in AU BUT it doesn t tell us about the actual size of the orbit in kilometers RADAR is used to determine the actual distances in the solar system 1Short pulse of radio waves is directed towards a planet 2 The waved is reflected at the planet and a return pulse or echo comes back 3 The measurement includes the amount of time the radio wave takes to complete a roundtrip Example It takes about 300 seconds to receive an echo back from Venus to Earth This makes the one way travel time 150 seconds Venus is 03 AU from Earth at the closest point Speed Distance x Time Isaac Newton 16421727 17th Century British mathematician 1 Developed Newtonian Mechanics 2 3 Laws of Motion Theory of Gravity and Calculus development help presently to explain all motion including those of planets 3 These laws break down only in extreme cases Newton s First Law An object at rest remains at rest and a moving object continues to move forever in a straight line with constant speed unless some external force changes their state of motion Newton s Second Law The acceleration of an object is directly proportional to the net applied force and inversely proportional to the object s mass aF m Fm a Thursday September 3 2015 If two objects are pulled with the same force the one with the greater mass will accelerate less If two identical objects same mass are pulled with different forces the one pulled with the greater force will accelerate more Newton s Third Law Whenever one body exerts a force on a second body the second body exerts an equal and opposite force on the first For every action there is an equal and opposite reaction Gravity Newton realized that any object having mass exerts an attractive gravitational force on all other objects having mass Newton s Law of Gravitation The gravitational force F between two bodies directly proportional to the product of the masses M and m and inversely proportional to the square of the distance between them F G M m rquot2 F Force G Constant M Mass of one object m mass of other object r distance between them don t forget to square Weight and Mass 0 Weight is the force due to the gravitational attraction of a body by the Earth 0 Mass is the amount of matter
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