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ASTRONOMY • The study of celestial objects, space, and the universe • Considered one of the oldest disciplines of science • 3,000 – 4,000 years old CELESTIAL MOTION • The path a planet follows around the sun is called an ? ORBIT • The orbital movement of a celestial body around an object is called? REVOLUTION • The spinning or motion of a celestial body around an axis is called? ROTATION HISTORY • Utilized repeated observations of the night sky with the naked eye • Played a significant role in the development of civilization, used to develop the calendar and understand the seasons HISTORY • As civilization progressed astronomical observatories were constructed • Led to detailed maps of the night sky and ideas about the motion of the planets, Sun, Moon, and Earth. ARISTOTLE • Described the universe as a series of spheres containing the planets and Sun rotating around the Earth with the stars fixed against the background • “Motionless Earth” idea based on the philosophical idea that if you feel no motion there is no motion • Constellations did not appear to change position or size, no apparent parallax. PARALLAX • Is the change in the observed position of an object due to the change in location of the observer. • Planets appeared to move position in the night sky, while stars did not. • Stars too far away for a noticeable change in position with the naked eye PTOLEMY • 140 A.D., 5 centuries after Aristotle • Developed a mathematical model based on Aristotle’s teachings • Ptolemaic/Geocentric Model GEOCENTRIC MODEL • Earth is fixed at or near the center of the universe • Planets and the Sun move along a perfect circular path • Planets also follow a circular path, epicycle, that is centered along the circular path around the Earth Abyss.uoregon.edu COPERNICUS • Challenged the Geocentric Model in the 1500’s • Proposed the Heliocentric Model, planets follow circular paths around the Sun, not the Earth. • Maintained classical concept of uniform circular motion HELIOCENTRIC MODEL • Recognized as the “Copernicus Revolution”, placing the Earth along a similar orbit to that of the other planets. • Helped explain Retrograde Motion Stisci.edu RETROGRADE MOTION • When planets seem to move in the opposite direction across the night sky • Occurs because the planets move around the Sun not the Earth • The difference is speed also affects Retrograde Motion but did not fit the classical uniform circular models Redorbit.com KEPLER • In the early 1600’s abandoned the classical ideas of the circular and uniform motion of the planets • Studying the motions of Mars discovered the planets move in an ellipse rather than a circle • Noticed that the speed of Mars was not constant, but varied along its’ path ELLIPSE KEPLER’S LAWS OF PLANETARY MOTION 1ST LAW Planets orbit the sun along an elliptical path • Ellipse is an oval-like shape drawn around two focus points, foci. The distance from one focus to any point on the ellipse and then back to the other focus is a constant • The closer the foci the more circular the ellipse becomes, most planets are nearly circular KEPLER’S LAWS OF PLANETARY MOTION • 2nd LAW Planets move faster along their elliptical path the closer they are to the sun KEPLER’S LAWS OF PLANETARY MOTION 3rd LAW The farther a planet is from the sun, the longer it takes to complete the elliptical orbit • The semi-major axis is the average distance from the planet to the sun KEPLER’S LAWS • All of the laws are empirical, based on observation and data rather than theoretical • Kepler never knew what held the planets along their orbits or why they continued to revolve around the sun MODELS • Used to display, represent, and demonstrate the structure and behavior of the Cosmos • Allow scientists to test and observe behaviors on a smaller scale • Models of our Solar System TOOLS & TECHNOLOGY • Astronomer’s study the light that reaches Earth from distant objects in space • Light is a form of electromagnetic radiation • Electromagnetic Radiation is a form of wave-like energy emitted by the acceleration of a charged particle by a force ELECTROMAGNETIC WAVES • Do not require a medium, can travel in space • Travel at a speed of 300,000 km/s through space, speed of light. • Represents a spectrum of different wavelengths ELECTROMAGNETIC SPECTRUM R O Y red orange yellow G. green B I blue indigo V violet TELESCOPES • Used to aid astronomers in the collection of light normally not visible to the naked eye. • collect more light • over a longer period of time • better image from space Popularmechanics.com SATELITES & PROBES • Atmosphere blocks certain wavelengths of electromagnetic radiation • Why does this matter? Nasa.gov How do they do it??? Nasa.gov ORIGIN OF THE UNIVERSE Big BANG Theory 1. Expansion of a single unstable dense collection of matter and space 2. Gases, dust, particles and energy exploded outward 3. Gases and particles cooled/condensed into planets, stars, & galaxies 4. Matter and space still expanding out from explosion 5. Red Shift demonstrates present day expansion RED SHIFT EXPANSION • Light observed from distant galaxies have light shifted toward the red side of the spectrum. • The shift toward “red” is due to an increase in wavelength due to the DOPPLER EFFECT UNIVERSE GALAXIES SOLAR SYSTEMS MILKY WAY GALAXY • “via lactae” latin for Milky Way • “Milky” band appearance created by diskshape of our galaxy viewed from within • Millions of stars and planets, including our solar system • All orbit the proposed “black-hole” center Our Solar System • Formed by a Solar Nebula (4.6 bya) • Hot dense center of cloud condenses into the Sun • Disk-like cloud of gases surrounding Sun has various regions of temperature • Different elements cool, condense, and combine in different regions Universetoday.com THE SUN • Largest object in our solar system • 99% of the mass of our solar system • Large mass = strong gravitational force, resulting in the orbits of all the planets GRAVITY • Gravitational force is a force of attraction dependent on the mass and distance between two objects. • Described by Sir Issac Newton in 1687 as the Law of Universal Gravitation THE SUN • The sun’s energy comes from Nuclear Fusion • Nuclear Fusion – small light nuclei (hydrogen atoms) are combined to form larger nuclei (helium atoms) resulting in the release of ENERGY • E = mc2 NUCLEAR FUSION SUN’S ATMOSPHERE • Photosphere – 6,000 K – Surface, yellow-color • Chromosphere – 30,000 K – Only visible during solar eclipse, reddish • Corona – 1- 2 million K – Only visible during solar eclipse, white – Solar Winds SOLAR WIND • Originate in the Corona • Stream of charged atoms known as “ions” • Collide with Earth’s magnetic field creating the Auroras. Harvard.edu Nationalgeographic.com SOLAR ACTIVITY • Changes in the Sun’s atmosphere • 11 year cycles • Sunspots and Solar Flares • Interfere with phone, TV, and radio reception • Affects climate on Earth Nasa.gov INNER PLANETS – terrestrial planets – dense, small, have solid rocky surfaces, metal cores OUTER PLANETS – Jovian Planets – less dense, large, gaseous, thick atmosphere “My Very Eager Mother Just Served Us Noodles” • 3rd planet from the Sun • Nearly circular orbit • Moderately dense atmosphere – 78% Nitrogen 21% Oxygen – Greenhouse Effect • Water – Solid, Liquid, Gas EARTH EARTH’S MOTION • Rotation – Earth rotates around an axis – Night and Day – 24 hours • Revolution – Earth revolves around the Sun, Heliocentrism – Seasons – 365 days = 1 year EARTH’S ROTATION • • • • • Rotates along a tilted axis, 23.5o Rotates West to East Mean Solar Day = 24 hours 15o / hour rotation The “day” is getting longer due to tidal friction • inertia Astro.psu.edu EARTH’S ROTATION • Precession – a slow gradual change in the orientation of a rotational axis • “wobble of a top” • Due to the gravitational influences of the Sun, Moon, and other celestial bodies. • Would it affect Polaris, the North Star? Geography.hunter.cuny.edu EARTH’S ROTATION • The gravitational forces of the Sun and Moon vary over time • Creates a variation in the speed of precession. • Variation in gravitational forces and the speed of precession create a NUTATION of the Earth’s axis EARTH’S ROTATION • Nutation – a slight variation in the precession of the Earth’s rotation • From nutare, latin for “to nod” • “nodding” due to the Moon Ucar.edu EARTH’S REVOLUTION • Revolves around the Sun in an almost circular orbit • 1 AU = 150 million km • one revolution = 365 days • one revolution = one orbital period • Seasons • Hemisphere that tilts towards the Sun has summer • (more direct sunlight) • Hemisphere that tilts away from the Sun has winter • (less direct sunlight) • summer solstice: longest sunlight hours of the year • June 21st-first day of summer • winter solstice: shortest sunlight hours of the year • Dec. 21st- first day of winter • spring equinox: equal amounts of day/night hours • March 21st- first day of spring • fall equinox: equal amounts of day/night • Sept. 21st- first day of fall EARTH’S REVOLUTION • The Earth does not revolve around the center of the Sun! • The Earth revolves around the center of mass of the Solar System • This center of mass which objects orbit is called the barycenter • The barycenter of the Solar System lies within the Sun Barewalls.com Lhup.edu THE MOON • Earth’s only natural satellite • Moon’s diameter 27% of the Earth’s diameter • Impact Theory – formed by a collision between Mars-sized object and the proto-Earth Universetoday.com Nasa.gov THE MOON • Synchronous Rotation – the Moon’s rotational period is equal to it’s orbital period. • 1 rotation = 1 revolution • One complete revolution or “orbital period” is 27.3 days • Lunar Month 29.5 days due to position in relation to the Sun THE MOON’S GRAVITY • Gravitational influence on Earth decreases the “bulge” along the equator • Gravitational influence on the oceans, creating the tides. Lhup.edu TIDES • Due to the gravitational influence of the Moon and the Sun • Moon and Sun pull in perpendicular directions, Neap tides. • Moon and Sun pull in same/opposite directions, Spring tides. ECLIPSES • Moon passes directly between the Sun and the Earth blocking our view of the Sun Solar Eclipse • Moon passes through the Earth’s shadow Lunar Eclipse Nasa.gov Why are solar and lunar eclipses so rare????