ASTRO 101 Fall 2015 CHAPTER ONE Earth centered geocentric universe Cosmic address our place in the universe Galaxy great Island of stars in space Ex Milky Way large galaxy with over 100 billion stars located half way from the galactic center to the edge of the galactic disk Local Group Milky Way is the second largest amongst 40 galaxies in our Local Group Galaxy clusters galaxies with more than a few dozen members Supercluster s regions which galaxies and galaxy clusters are tightly packed Our Local Group is located on the outside of the Local Supercluster Universe sum of total of all matter and energy encompassing all superclusters and everything Average distance between galaxies is INCREASING Big Bang began 14 million years ago Galaxies and galaxy clusters DO NOT expand individually Life Cycles star is born when gravity compresses material in a cloud to a point where the center becomes dense and hot enough to generate energy through nuclear fission Nuclear fission process which light weight atomic nuclei smash together and stick to make heavier nuclei Astronomical Unit AU average distance between Earth and Sun 150 million km Light year distance that light can travel in one year 9 46 trillion km Observable Universe portion of entire universe that can be seen from Earth only a tiny portion Star system stars and any planets material that orbit within it Early universe contained only simplest elements hydrogen and helium Earth and humans are made up primarily of Carbon Nitrogen Iron and Oxygen elements were manufactured by stars through nuclear reactions and nuclear fission CHAPTER TWO Constellation region of the sky with well defined borders Celestial sphere stars that surround Earth North Celestial Pole point directly over Earth s North Pole South Celestial Pole point directly over Earth s South Pole Celestial Equator projection of Earth s equator into space makes a complete circle around the celestial sphere Ecliptic path the Sun follows as it appears to circle around the celestial sphere once a year EX ecliptic celestial equator north celestial pole south celestial pole Local sky the sky as seen from wherever you happen to be standing Horizon boundary between Earth and the sky Zenith point directly above Meridian imaginary half circle stretching from the horizon due south through the zenith due north Zenith Meridian Horizon Angular size angle it appears to span in your field of view depends on distance does not give objects true size Circumpolar bodies remain above horizon and make daily counter clockwise circle around N celestial pole Angular distance the angle that appears to separate them Arcminutes astrological measurement between stars each degree 60 arcminutes each arcminute 60 arc seconds stars in N celestial pole NEVER rise or set stars near the south celestial pole NEVER rise above the horizon all other stars have daily circles below and above the horizon Latitude N S position Longitude W E position The altitude of the celestial pole in your sky is equal to your latitude Zodiac constellations along the ecliptic 13 constellations the Sun s apparent location along the ecliptic determines the constellations seen Earth s tilted axis causes sunlight to fall different on Earth at different times of the year 23 hours 56 minutes for the Earth to rotate sidereal day 24 hour day solar day AVERAGE TIME it takes the SUN to make one circuit throughout the sky 361 degrees New Moon Waxing growing Crescent First Quarter Waxing Gibbous shrinking Full Moon Waning Gibbous Third Quarter Waning Crescent Solstice sunlight becomes the most extreme for both hemispheres Equinox hemispheres are equally illuminated Spring and Fall Equinox March 21 and September 22 Winter and Summer Solstice December 21 and June 21 Precession gradual wobble that changes the orientation of the Earth s axis in space does not affect season s axis tilt Lunar phases Lunar eclipse Earth lies directly between Sun and Moon Moon disappears when a full moon occurs Solar eclipse moon lies directly between Sun and Earth moon s shadow falls on Earth Sun is blocked when new moon occurs Nodes two points in each orbit at which the moon crosses the surface Umbra sunlight is completely blocked Penumbra sunlight is partially blocked Total lunar eclipse moon passes through Earth s umbra Partial lunar eclipse part of full moon passes through umbra Penumbral lunar eclipse moon passes only through Earth s penumbra Penumbra Umbra Totality time during which the moon is entirely engulfed in the umbra Total solar eclipse moons umbra touches Earth s surface Partial solar eclipse only part of the Sun is blocked from view Annular eclipse ring of sunlight surrounding the moon hard to predict Moon s umbra DOES NOT reach Earth Saros cycle nodes 29 5 day lunar phase cycle cycle of 18 years 11 333 days Apparent retrograde motion reverse course moving westward toward zodiac more distant planets move slower from Sun than closer planets Stellar parallax stars appear to differ in distance because of our orbit parallax shift in positon depends on distance CHAPTER THREE Model conceptual representation created to explain and predict observed phenomenon Geocentric model Earth centered model created by Greek philosophers Ptolemaic model each planet moves on a small circle whose center moves around Earth on a larger circle epicycle planets small circle around Earth deferent planets larger circle around Earth Copernican Revolution origin of modern science discovered geometric relationships calculated planets orbital period around Sun distance from Sun in terms of Earth Sun distance SUN CENTERED fatal flaw he believed motion was in perfect circles poorly made like Ptolemaic model Tycho discovered a nova new star farther than Moon discovered explanation for planetary motion planets orbit Sun but Sun orbits Earth incorrect because unable to detect stellar parallax Kepler apprentice of Tycho s discovered the elliptical shape of planetary orbits Foci Ellipse special oval Foci single focus Semi major axis half of ellipse axis Minor axis short axis Eccentricity quantity that describes amount by which an ellipse is stretched out compared to a perfect circle circle has ZERO eccentricity the greater the eccentricity the more elongated the ellipse Kepler s Laws of Planetary Motion Major axis Semi major axis 1 The orbit of each planet about the Sun is an ellipse with the Sun at one focus A planets distance from the Sun varies during its orbit Closest at its perihelion
View Full Document
Unlocking...