Introductory AstrSolar System
Introductory AstrSolar System ASTR 111
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Vagabond ofthe SOIaF firg ASTR 111 003 Fall 2007 Lecture 13 Nov 26 2007 Introduction To Modern Astronomy I Solar System Introducing Astronomy Chap 1395 Ch7 Comparative Planetology Ch8 Comparative Planetology Ch9 The Living Earth Ch10 Our Barren Moon Planets and Moons Ch11 Mercury Venus and Mars Chap 715 Ch12 Jupiter and Saturn Ch13 Satellites of Jupiter amp Saturn Ch14 Uranus Neptune and Beyond Ch15 Vagabonds of Solar System Sun and Life Highlights Chap 16 amp 28 Discovery of Asteroids Hunt for missing planet TitiusBode Law as a rule of thumb from one planet to the next the orbit size increases by a factor between 14 and 2 However Jupiter 52 AU is more than 3 times farther from the Sun than Mars 152 AU A missing planet between 2 and 3 AU Ceres was found in 1801 the largest asteroid diameter of 918 km Distance 277 AU from the Sun 46 years orbit period It is also called minor planet or dwarf planet Pallas was found in 1802 522 km at 277 AU Vesta was found in 1807 Discovery of AsterOIds 300000 asteroids have been quot 7 quotI found 5000 more each month Three asteroids have diameter more than 300 km 39 I 39 g I 200 asteroids are bigger than 100 I H I I a 39 39 km across Thousands of asteroids with diameters larger than 1 km The vast majority are less than 1 km Asteroid Belt Asteroid belt the region Most asteroids orbit the Sun in a belt about where most asteroids orbit e quot 39 li i i g the Sun at distances saga between 2 and 35 AU It is between Mars and quot macaw Jupiter quot The average distance between asteroids is about 1 Jupiter The Asteroid Belt Asteroid Formation Asteroids are relics of planetesimals that failed to accrete into a fullsized planet because of the influence of Jupiter s gravitational force Without the effect of Jupiter an Earthsized planet might form in the asteroid belt Jupiter s gravitational pull clears out the asteroid belt by ejecting most of the planetesimals into the deep space The few planetesimals remaining become the asteroids that we see today Combining all the asteroids would produce an object of only 1500 km in diameter Asteroid Formation Gravitational perturbation by Jupiter continues to deplete certain orbits within the asteroid 4 belt The resulting gaps called Kirkwood gaps occur at simple fractions eg 12 13 of Jupiter s orbital period caused by resonance effect 0 The repeated alignment at the same location and with Distance from the Sun AU 3 4 Kirkwood gaps are regions where rhere are relatively fejv ageroids 300 N O o I 0rbit of Jupiter 100 Trojan I asteroids I I Number of known asteroids OrbitafEarth I OrhitofMars l E 7 Orbital period Jupi er s rbita period 1 the same orientation Kirkwood Gaps in Aster0id Belt eventually ejects an object from its orbit Asteroid Properties Asteroids are rocky objects Asteroids are often of irregular shape or potato likequot shape Gravitational force is not strong enough to compress matter into spherical shape Asteroid Properties An asteroid may not be a single piece of solid rock An asteroid may be a rubble pile of small fragments of rocks fitting together loosely by mutual gravitational force Mathilde has a low density of 1300 Large crater kgm3 likely a rubble pile in shadow A rubble pile can survive violent collision Soft impact instead of shattering impact Can produce large craters Caused by impacts among asteroids Asteroid outside the main belt Trojan asteroids Over one thousand Trojan asteroids have been found at the two Lagrange points along the Jupiter s orbit Lagrange point stable point due to the combined gravitational forces of the Sun and Jupiter about 60 d 1 J 39t egree away rom Upl er IW Lagrange point I I I I I I I I 39k 7 i 7 7 I O The Trojan asteroids are quot60 trapped at two stable Jupiter L 3 3 r 39 ule 600 combined gravitational 5quot forces ofthe Sun and Jupiter 7 5 Trojan asteroids and 39 L Lagrange pomts pfquot9ek I Asteroid outside the main belt NEO nearEarth object Asteroids that cross Mars s orbit due to high eccentricity or orbits lie completely within that of Mars More than 4100 NEOs have been detected 7 b A map of all asteroids within Jupiter39s orbit Asteroid Impact the Eart NEOs impact the Earth 5 Miniimpact by meteorite New York Oct 9 1992 p Tunguska Event 1908 Seared and felled the trees in an area of 50 kilometer in diameter By an 80m diameter asteroid Aeteroid lmpactthevlwiarth i i wquot m The Barringer Crater Arizona 12km wide and 200 m deep Occurred 50000 year ago By a 50m diameter asteroid Asteroid Impact the Earth An asteroid impact may cause the extinction of the dinosaurs and many other species 65 million year ago An iridiumrich layer within limestone strata was discovered 1979 Found at numerous site around the world Geological dating reveals deposition 65 million years ago 439 i 35quot x A J 9 I 1 V By a 10km diameter asteroid The site is possibly the 180km diameter Chicxulub crater on the Yucatan Peninsula Mexico Meteoroid Meteor Meteorite Meteoroid small chuck of rock in space Like an asteroid but smaller Asteroid generally larger than 50 meters across Meteor the brief flash of light caused by a meteoroid when it enters the Earth s atmosphere and produces a fiery trail across the night sky The glowing is the result of intense heat caused by atmospheric friction oMeteorite lf part of the object survives the fall the fragment that reaches the Earth s surface is called a meteorite Meteorites Properties oMeteorites have different types of different origins Stony meteorites 95 from small undifferentiated asteroids Stony iron meteorites 1 from crust of large asteroids lron meteorites 4 from core of large differentiated asteroids About 300 tons of extraterrestrial matter falls on the Earth each day mostly in the form of dust lmdmamnshai by interlocking crystals in a W Widmanstiitten pattern polished they reveal tiny specks of iron in the rock 1 Stony type Stonyiron type Iron type Meteorites Properties Radioactive agedating indicates that meteorites are 456 billion years old indicating the age of the solar system Rare stony meteorites called carbonaceous chondrites may be relatively unmodified material from the solar nebula These meteorites often contain organic material and may have played a role in the origin of life on Earth Allende Meteorite Mexico Feb 8 1969 Comet A comet is a chunk of mixture of ice and rock lt become luminous when it passes near the Sun through evaporation of ice and dust Unlike asteroids a comet generally moves in a highly elliptical orbit about the Sun Comet strucure Nucleus Coma Dusttail Hydrogen envelope Dust tail Hydrogen Ion Tail e quote39 39 e Ion tail Comet structure Nucleus The solid part of a comet Mixture of ice and dust Typically several kilometer across eg City size Nudcu s Impact Cl39 tt39il39 a Cornet Halley b Comet Tempe 1 Comet structure Coma the fuzzy luminous ball produced by the liberated gas and dust as the comet near the Sun Typically 1 million km in diameter The visible head of the comet Comet structure Hydrogen envelope A huge sphere of tenuous hydrogen gas typically about 10 million km in diameter Hydrogen comes from water molecule that breaks apart when absorb ultraviolet photons from the Sun A L thecometstail I cometsImmensehydrogenenvelope V Visible Ultraviolet can not been seen from ground Comet structure Tails About 100 million km in length almost 1 AU Dust tail formed by the radiation pressure on the finegrained dust particles in the coma Radiation pressure photons from the Sun exerts a pressure on any object that absorbs or reflects them Dust particles slowly drift away forming a curved tail White color dust reflecting of sunlight Ion tail Light Ionized atoms and molecules are swept directly away by solar wind to form the straight ion tail The distinct blue color is caused by emission from carbonbearing molecules such as CN and CZ Comet structure Comet Orbits Comets have highly elliptical orbits indicating they come from the outer part of the solar system Comets often have highly inclined orbits not on the ecliptic plane indicating a different origin from planets and asteroids Jupiter s Comet39s orbit Saturn39s orbit Uranus39s 1983 orbit Neptune s orbit plutors Comet Halley s orbit position at given date Perihelion 1 948 2024 Comet Origin From two large reservoirs Kuiper Belt and Oort Cloud Kuiper belt lies in the plane of the ecliptic at distances between 30 Neptune s orbit and 50 AU from the Sun contain tens of thousands of comet nuclei Produce Jupiterfamily comets which orbit the Sun in fewer than 20 years and return at predictable interval Oort cloud A sphere extending from the Kuiper Belt to some 50000 AU from the Sun contains billions of comet nuclei Intermediate period 20 to 200 years and longperiod comets 1 to 30 million years are thought to originate in the Oort cloud Comet Origin Oort Cloud created 456 billion m years ago from m Kuiper belt and outer numerous Icy s013 sys mplmmv ms planetesimals in the vicinity of the newly formed Jovian planets These planetesimals were ejected into the outer solar system by the gravity of Jovian planets Comet Meteor Shower Meteoritic swarm as a comet s nucleus evaporates residual dust and rock fragments form a loose collection of debris that continues to circle the Sun along the comet s orbit A comet may lose about 1 of its ice each time it passes near the Sun It may eventually breakup after many passes Comet Meteor Shower Meteor shower it happens when the Earth s orbit happens to pass through a meteoritic swarm Plane of meteoroids39 orbit lfa comet is only A W 7 7 i recently extinct s over the ages the its fragments will 39 comet fragments i 7 still be concentrated i Spread out along in a compact swarm quot1 Old comet39s elliptical orbit 7 Plane of l Earth s orbit Comet Meteor Shower til 17 Prominent Yearly Meteor Showers Quadrantids January 3 40 4O Bo ites Lyrids April 22 15 50 Lyra Eta Aquarids May 4 20 64 Aquarius Delta Aquarids July 30 20 40 Aquarius Perseids August 12 50 60 Perseus Orionids October 21 20 66 Orion Taurids November 4 15 30 Taurus Leonids November 3916 15 70 Leo Geminids December 13 50 35 Gemini Ursids December 22 3915 35 Ursa Minor Thz date of maximum intensity is the best time to observe a particular shower altrough good displays can often be seen 1 day or two befme or after the nmximum The typical hourly rate is given for an o sener undzr optimum Viewing conditions The average speed refers to how fast the meteoroids are moving when they strike the atmosphere 2 W C Comparative Planetollogy W The Origin of Our Solar System Chapter Eight ASTR 111 003 Fall 2006 Lecture 08 Oct 23 2006 Introduction To Modern Astronomy Ch7 Comparative Planetology I IntrOdUCing AStronomy Ch8 Comparative Planetology II Chap 16 Ch9 The Living Earth Cth Our Barren Moon Chl l SunScorched Mercury Planets and Moons Ch12 Cloudcovered Venus Chap 717 Ch13 Red Planet Mars Chl4 Jupiter and Saturn ChlS Satellites of Jup amp Saturn Chl6 Outer World Chl7 Vagabonds of Solar System N 091er Guiding Questions What must be included in a viable theory of the origin of the solar system Why are some elements like gold quite rare while others like carbon are more common How do we know the age of the solar system How do astronomers think the solar system formed Did all of the planets form in the same way Are there planets orbiting other stars How do astronomers search for other planets Models of Solar System Origins Scientific Methods Any model of solar system origins must explain the presentday Sun and planets 1 The terrestrial planets which are composed primarily of rocky substances are relatively small while the Jovian planets which are composed primarily of hydrogen and helium are relatively large 2 All of the planets orbit the Sun in the same direction and all of their orbits are in nearly the same plane 3 The terrestrial planets orbit close to the Sun while the Jovian planets orbit far from the Sun Abundances of Chemical Elements Hydrogen makes up nearly threequarters of the combined mass of the Sun and planets Helium makes up nearly onequarters of the mass Hydrogen and Helium together accounts for about 98 of mass in the solar system All other chemical elements combined make up the remaining 2eg oxygen carbon nitrogen Iron silicon The 10 most abundant elements gt X 10 g 11 1HydrogenH 5 NeonNe 8MagnesiumMg 10 2 Helium He 6 Nitrogen N 95iliconl5i 5 3 Oxygen O 7 Iron Fe 10 Sulfur S quot5 4Carbon C t 8 i3 39 1 31 939 7 39 arr 5 1 7 Vii o 6 5 1 5 l i i r 7 gt 3 10 gt i i i 5 10quot i i i 392 3 i 3 10 i i 21 i i 2 10 i quoti i i E i hi i i i i i 1 i i g 1 2 3 4 5 6 7 8 9 1011 1213141516171819 20 21 22 23 24 25 26 27 28 29 30 Atomic number gt Abundances of Chemical Elements The dominance of hydrogen and helium is the same as in other stars and galaxies throughout the universe Hydrogen and helium atoms are produced in the Big Bang which created the universe 137 billion years ago All heavier elements were manufactured by stars later Thermalnuclear fusion reaction in the interior of stars Violent explosions so called supernovae that make the end of massive stars As stars die they eject material containing heavy elements into the interstellar medium New stars form from the interstellar medium with enriched heavy elements Solar system contains recycled material from dead stars Abundances of Chemical Elements The interstellar medium is a tenuous collection of gas and dust that pervades the spaces between the stars Dustreflectingstarlight Solar System s Age The solar system is believed to be about 456 billion years old Radioactive agedating is used to determine the ages of rocks Radioactive elements decay into other elements or isotopes The decay rate measured in half life is constant for radioactive element eg Carbon 14 5730 years eg Rubidium 87 47 billions year By measuring the numbers of the radioactive elements and the newlycreated elements by the decay one can calculate the age Solar System s Age All Meteorites show nearly the same age about 456 billion years Meteorites are the oldest rocks found anywhere in the solar system They are the bits of meteoroids that survive passing through the Earth s atmosphere and land on our planet s surface On the Earth some rocks are as old as 4 billions years but most rocks are hundreds of millions of years old Moon rocks are about 45 billion years old Solar Nebula Hypothesis The Sun and planets formed from a common solar nebula Solar nebula is a vast rotating cloud of gas and dust in the interplanetary space The most successful model of the origin of the solar system is called the nebular hypothesis CI A diffuse roughly spherical slowly rotating nebula begins to contract Solar Nebula Hypothesis The nebUIa began to a Adiffuseroughlysphericalslowly contract about 456 bill Ion rotating nebula gagins to contract years ago because of its 39 39 own gravity As it contracted the greatest concentration occurred at the center of the nebula forming a re I atively d e n se reg i0 n b As a result of contraction and rotatior flat 39dl l t39 d39 kf Th tt 39 called the protonsun 222412242 anthem sh protosun As it contracted the cloud flattens and spins more rapidly around its rotation axis forming the disk 39 Solar Nebula Hypothesis As protosun continued to contract and become denser its temperature also increased because the gravitational energy is converted into the thermal energy After about 10 million years since the nebula first began to contract the center of the protosun reached a temperature of a few million kelvin At this temperature nuclear reactions were ignited converting hydrogen into helium A true star was born at this moment Nuclear reactions continue to the present day in the interior of the Sun Solar Nebula Hypothesis Protoplanetary disk the disk of material surrounding the protosun or protostars are believed to give birth to the planets The flattened disk is an effect of the rotation of the nebula The centrifugal force of the rotation slows down the material on the plane perpendicular to the rotational axis fall toward the center But the centrifugal force has no effect on the contraction along the rotational axis Disk Star Formation of Planets The protoplanetary disk is composed by gas and dUSt gt Diskofgasand dust Asubstance is in the sate of either solid or gas but not in liquid if the pressure is sufficiently low Central star blocked out in telescope to make disk visible 9 Size of Pluto s orbit Formation of Planets Condensation temperature determines whether a certain substance is a solid or a gas Above the condensation temperature gas state Below the condensation temperature solid sate Hydrogen and Helium always in gas state because concentration temperatures close to absolute zero Substance such as water H20 methane CH4 and ammonia NH3 have low concentration temperature ranging from 100 K to 300 K Their solid state is called ice particle Rockforming substances have concentration temperatures from 1300 K to 1600 K The solid state is often in the form of dust grain Formation of Planets In the nebula temperature decreases with increasing distance from the center of the nebula In the inner region only heavy elements and their oxygen compounds remain solid eg iron silicon magnesium sulfur They form dust grains In the outer region ice particles were able to survive Temperature K Methane condenses to form ice gt yn uto 4 Pi l 01 02 05 10 20 50 10 20 40 Distance from center of solar nebula AU I 101m 001 mm Dust grain Formation of Planets In the inner region the collisions between neighboring dust grains formed small chunks of solid material Planetesimals over a few million years these small chucks coalesced into roughly a billion asteroidlike objects called planetesimals Planetesimals have a typical diameter of a kilometer or so 0 Within the disk that surrounds the protosun solid grains collide and clump together into planetesimals Protosun PlaneteSImals Formation of Planets Protoplanets gravitational attraction between the planetesimals caused them to collide and accumulate into stilllarger projects called protoplanets Protoplanets were roughly the size and mass of our Moon During the final stage the protoplanets collided to form th e b The terrestrial planets built up by collisions and by the accretion of planetesimals by gravitational attractionThe Jovian planets formed by gas accretion Terrestrial planets Jovian planets Planets Solar system Formation of Planets Protoplanets gravitational attraction between the planetesimals caused them to collide and accumulate into stilllarger projects called protoplanets Protoplanets were roughly the size and mass of our Moon During the final stage the protoplanets collided to form th e b The terrestrial planets built up by collisions and by the accretion of planetesimals by gravitational attractionThe Jovian planets formed by gas accretion Terrestrial planets Jovian planets Planets Solar system Formation of Planets In the outer region more solid materials were available to form planetesimals In addition to rocky dust grains more abundant ice particles existed Planetesimals were made of a mixture of ices and rocky materials In the outer region protoplanets could have captured an envelope of gas as it continued to grow by accretion this is called core accretion model Gas atoms hydrogen and helium were moving relatively slowly and so easily captured by the gravity of the massive cores The result was a huge planet with an enormously thick hydrogenrich envelope surrounding a rocky core with 510 times the mass of the Earth Finding Extrasolar Planets In 1995 first extrasolar planet was discovered by Michel Mayor and Didier Qieloz of Switzland As of Oct 22 2006 199 extrasolar planets have been found STAR PLANETS 39 O o our sun MERCURY VENUS EARTH MARS 47 Ursae 39 Majoris Upsilon A Andromedae 39 069 MJup 39 289 MJup 375 MJup HD114762 I 1103MJup Rho Coronae I l 10 15 Semimajor axis of orbit AU 0 9 01 E o N 01 Finding Extrasolar Planets Extrasolar planets can not be directly observed because their reflected light is about 1 billion times dimmer than that of their parent stars Their presence is detected by the wobble of the stars The wobble motion of star is caused by the gravitational force of the planets The wobble motion can be detected using Doppler effect 39 Center of Planet mass Angular diameter of sta r s j wobble 1 W I I Blueshifte39d 7 light from I star a Redshifted V light from star 0 A star and its planet b The astrometric method c The radial velocity method ASTR 111 003 Fall 2006 Lecture 02 Sep 11 2006 Introduction To Modern Astronomy ll Ch1 Astronomy and the Universe IntrodlzCLng A1Stgnomy gt Ch2 Knowing the Heavens 0 ap Ch3 Eclipses and the Motion of the Moon Ch4 Gravitation and the Waltz of the Planets Ch5 The Nature of Light Ch6 Optics and Telescope Planets and Moons chap 717 Chapter Two Hawaii latitude 20 deg Washington DC latitude 38 deg NF 91 9 NT 00 Guiding Questions What role did astronomy play in ancient civilizations Are the stars that make up a constellation actually close to one another Are the same stars visible every night of the year What is so special about the North Star Are the same stars visible from any location on Earth What causes the seasons Why are they opposite in the northern and southern hemispheres Has the same star always been the North Star Can we use the rising and setting of the Sun as the basis of our system of keeping time Why are there leap years Astronomy in ancient civilizations Positional astronomy the study of the positions of objects in the sky and how these positions change Nakedeye astronomy the sort that requires only human vision no telescope Has roots in almost all ancient civilizations Mayan Observatory Yucatan Peninsula Central American Astronomy in ancient civilizations Positional astronomy using naked Eyes Position of stars ecliptic orbit consterllations Path of Sun Moon Planets zodiac band 1 II L L Ancnent stronomlca Instrument Purple Mountain Observatory Nanjing China Constellations quot quot Constellations from the Latin for group of stars Ancient peoples looked at the stars and imagined groupings made pictures in the sky We still refer to many of 39 these groupings 3939 O Rigel Orion the Hunter Betelgeuse the armpit Mintaka the belt Eightyeight constellations entire sky On modern star charts the entire sky is divided into 88 regions Each is a constellation Most stars in a constellation are nowhere near one another in real 3D distance They only appear to be close together because they are in nearly the same direction as seen from Earth LEPUS 775 ly quotg39 Diurnal Motion of Stars Stars appear to rise in the east slowly rotate about the earth and set in the west This diurnal or daily motion of the stars is actually caused by the 24hour rotation of the eanh Earth is a rotating sphere illuminated by Sunlight Diurnal Motion of Stars Rotation of he Earth k Andromeda is Illuminated Dark day side Ifquot night side Andromeda gt Light from k the sun 1 k Rotation of overhead as seen Person in from California California midnight local time gtngnus the Earth Perscn in Cygnus is overhead as California seen from California 800 PM local time K a Earth as seen from above the North Pole b 4 hours onesixth of a complete rotation later View from the vantage point of above the North Pole Earth rotates counterClockwise from west to east View from people on Earth Stars rotates Clockwise from east to west Annual Motion of Stars Earth s orbit 0 Perseus The stars also appear to slowly shift in position throughout the 39 year when viewed at the same time eg midnight at the same location on the Earth 1 Earth in November Light from The shift is due to the orbit of e 5quot Earth in the earth around the sun f September If you follow a particular star on Wm VJ successrve evenlngs you Will it quotquot35quotquot Aquotd39 39 d find that It rlses approximately 4 ugh from minutes earlier each nIght or 2 the Sun mammalian hours earlier each month quoteE quotquot Annualmotion the star fgh hmmy pattern In the evening eg v midnight will be exactly the same after one year Winter Triangle Three of the brightest stars in the winter evening in the northern hemisphere CANIS MINOR Procyon Southern horizon Summer Triangle Three of the brightest stars in the summer evening in the northern hemisphere 39 V iAQUILA quotNorthern CroSs 0 01quot quot DELPHINUS Eastern horizon North Star Polaris Visibe anywhere in the northern hemisphere The position of the extended Earth rotation axis into the sky The North direction can be found by drawing a line straight down to the horizon URSA MINOR quotLittle Dipperquot BOOTES 13 H Polaris Arcturus o i 7 NR quotNorth Starquot 39 quot o o URSA MAJOR quotBig Dipperquot Western horizon Celestial Sphere Celestial sphere an imaginary sphere that all starts are fixed on its surface in the sphere all stars are assumed in the same distance Note that it is an imaginary object i WWimie that has no basis in physical reality However it is a model that remains 511quot 99 a useful tool of positional cam astronomy since it represents well W the diurnal motion by assuming the whole sphere rotates in a daily basis I l Celestial Sphere Ceestia equator Earth s equator projected out into space divides the sky into northern and southern hemispheres elestial sphere Celestia poles Earth s axis of rotation intersect the celestial sphere North celestial pole Celestial I I South celestial pole equator Vernal equinox V 39POIariS iS leSS than 10 39 away from the north celestial pole Celestial Sphere coordinates tools in Box 21 Ceestia coordinates Denote position of objects in elestial sphere 7 the sky 39 39 Based on Right Ascension and Declination Right Ascension O24h Corresponds to longitude Starting from Vernal Equinox the point where the Sun s path crosses the celestial equator in late March equator Vernal equinox I I I 39DeCIination 3990 Corresponds to latitude Celestial Sphere The celestial sphere appears tipped viewed gga f x by an observer eg at 439 Wquot 39 a 35 North Zenith Horizon Point in the sky directly overhead South celestial pole At 35 north latitude 39 the north celestial pole is 35 above the northern horizon the south celestial pole is 35 below the southern horizon At any time observer can see only half of the celestial sphere The other half is below the horizon The stars close to north pole never sets Celestial Sphere The apparent motion of stars at different latitudes b At the north pole ii i i H a At iddle northern latitudes c At the equator Seasons Spring Summer Autumn Winter Summer days are longer than 12 hours Winter days are shorter than 12 hours Seasons are opposite in the two hemispheres The Sun is higher in the summer at noon than in the winter Seasons the cause Seasons are caused by the tilt of Earth s axis rotation The Earth s axis is tilted about 2312 away from the orbital plane Spring in the northern hemisphere autumn In the southern hemisphere North POIE Winter in the northern hemisphere summer in the southern hemisphere North pole l South pole North pole 16 South pole Summer in the northern hemisphere winter in the southern hemisphere Ed39Ptquot 1 South pole Autumn in the northern hemisphere spring in the southern hemisphere Seasons Ecliptic the plane of the Earth annual orbit around the Sun also the plane of the Sun s annual orbit in the celestial sphere The Earth maintains this tilt as it orbits the Sun Spring in the northern hemisphere autumn In the southern hemlsphere Nm th PC39Ie Winter in the northern hemisphere summer in the southern hemisphere North pole South pole North pole 235 South pole South pole Summerin the northern hemisphere E I r winter in the southern hemisphere c 39P 39c Autumn in the northern hemisphere South pole spring in the southern hemisphere Seasons The summer is hotter because 1 the surface receives the Sun s light or heat longer the Earth is tilted toward the Sun Eg July in Northern Hemisphere Eg January in Southern Hemisphere As the Earth spins on its axis the surface spends more than 12 hours in the sunlight The days there are long and the nights are short 2 The Sun heats the surface more efficiently the Sun is high in the sky sunlight strikes the ground at a nearly perpendicular angle that heats the ground efficiently Seasons When the Sun is high in the summer the sunlight is more concentrated and thus increases the heating In the winter the Sun is lower the sunlight is less concentrated and thus reduces the heating l TheSunishighL l inthemidclay lsummersky ax a l le Sun is IolN 1th midday winter sky I so a shaft of l sunlight is l concentrated onto l a smallareawhich heats the ground effectively and makes the days warm l so the same shaft of l sunlight is spread out 3 1 over a larger area and H l less heating of the ll ground takes place a The Sun in summer Ecliptic Equinoxes Solstices North celestial pole EC39iPtiC utu nalequinox 39 Summersolstice Celestial equator I Vernal equinox South celestial pole Ecliptic Equinoxes Solstices Ecliptic a circular path the Sun appears to trace on the celestial sphere Ecliptic plane is tilted at 23 12 degrees to the celestial equator Equinoxesz the points that the ecliptic path and the celestial equator intersect There are only two points thus two equinoxes Vernal equinox the Sun crosses northward across the celestial equator Occurs on about March 21 Marks beginning of spring in northern hemisphere Autumnal equinox the Sun crosses southward across the celestial equator Occurs on about Sep 22 Marks beginning of autumn in northern hemisphere At equinoxes the day time is exactly 12 hours Ecliptic Equinoxes Solstices Summer Solstice the point on the ecliptic farthest north of the celestial equator Occurs on about June 21 marks the location of the Sun at the beginning of summer 1n the northern hemisphere the day time is the longest Winter Solstice the point on the ecliptic farthest south of the celestial equator Occurs on about Dec 21 marks the location of the Sun at the beginning of Winter in the northern hemisphere The day time is the shortest The Sun s Daily Path in Different Season Zenith Celestial equator North celestial pole i During In winter in summer in the northern i the northern hemisphere hemisphere the Sun rises in the northeast and sets in the northwest the southeast l and sets in the I On the first day of spring southwest and the first day of fall the Sun rises precisely in the east Timekeeping A day is the interval between the successive upper meridian transits of the Sun Meridian the northsouth circle on the celestial sphere that passes through the zenith and both celestial poles Noon defined as the Sun ze 39ith crosses the upper meridian Note meridian circle zenith and noon are all local in other words they depend on the location on the Earth I I 5 Horizon 2 m39 W Timekeeping A modern day is the mean solar day defined by the interval between successive upper meridian transit of the mean sun A mean solar day is exactly 24 hours long An apparent solar day varies over the course of the year Because the Earth s orbit is not a perfect circle Earth moves faster when it is near the Sun making the day longer Mean Sun is the imaginary sun that travels at a uniform rate the average of the apparent days over one year along the celestial equator Mean Sun produces a uniform mean solar day of 24 hours Ordinary watches and clocks measure mean solar time Timekeeping A modern day is the mean solar day defined by the interval between successive upper meridian transit of the mean sun A mean solar day is exactly 24 hours long throughout the year An apparent solar day varies over the course of the year Because the Earth s orbit is not a perfect circle Earth moves faster when it is near the Sun making the day longer Mean solar time is based on the motion of an imaginary mean sun along the celestial equator which produces a uniform mean solar day of 24 hours Ordinary watches and clocks measure mean solar time Time Zone and Universal Time For convenience of most people the Earth is divided into 24 time zones centered on 15 intervals of longitude around the globe UT universal time for convenience of aviator and sailors who regularly travel across time zones It is always the time in the zone that includes Greenwich England PACIFIC TIME MOUNTAIN CENTRAL TIME IME 4AM Vancou er 5 Sidereal Time tools in Box 22 To vernal equinox A Sidereal time a preferred time by astronomers It is based on the position of the star not the Sun It makes easier to track astronomical objects A sidereal day is the time between successive upper meridian passages of the vernal equinox 23h 56m Earth moves about 1quot around its orbit in one so Earth must make a complete to local solar noon on March 22 Local solar noon on March 21 is at this location on Earth Earth on v Earth on March 22 March 21 A sidereal day the time takes the Earth rotate exactly 360 A solar day the time takes the Earth rotate 360 plus 1 or 4 more min of rotation to make up the Sun s shift caused by orbital motion Calendar and Leap Years In modern calendar a year is 365 whole days and 366 whole days in leap years one more day on Feb 29 The reason is that the more accurate year the tropic year defined by the interval of successive vernal equinox transit of the Sun is not a whole number It is 3652422 days Julius Caesar s calendar assuming year36525 days The offset of 025 dayyear adds one more day in every 4 years Leap year the year can be evenly divided by 4 eg 2004 2008 Gregory Calendar Pope Gregory Xlll current calendar Dropped ten days from Oct 4 1582 to Oct 15 1582 brought the spring Sun passes the vernal equinox back to March 21 Because a tropic year is 11 minute offset from 36525 days This error adds up about three days in every four centuries Only century years evenly divisible by 400 should be leap years The Living Earth Chapter Nine ASTR 111 003 Fall 2006 Lecture 09 Oct 30 2006 Introduction To Modern Astronomy Ch7 Comparative Planetology I Introducing Astronomy Ch8 Comparative Planetology II Chap 16 Ch9 The Living Earth Cth Our Barren Moon Chl l SunScorched Mercury Ch12 Cloudcovered Venus Ch13 Red Planet Mars Planets and Moons Chap 717 Chl4 Jupiter and Saturn ChlS Satellites of Jup amp Saturn Chl6 Outer World Chl7 Vagabonds of Solar System Loom O l Guiding Questions What is the greenhouse effect How does it affect the average temperature of the Earth Is the Earth completely solid inside How can scientists tell How is it possible for entire continents to move across the face of the Earth How does our planet s magnetic field protect life on Eanh Why is Earth the only planet with an oxygenrich atmosphere Why are prevailing winds generally from the west over most of North America but generally from the east in Hawaii What are global warming and the ozone hole Why should they concern us Earth Data w39n me 211 of orb Incfination of em Diameter eqcuaioc39izi Mass 3 erage Jeiisiiy 1 12 511 s Almospheu39ic compesilion 7308 zincgen 032 95 cxygen 32 quot de 332 er GI Etns ecwles U 35 carbon c39io hy nu er vapor abouz 1 wat gt3 gt023 mml gtoltm 23036 gtoltm Comm gtoltm rmsq An Active Earth All activity in the Earth is powered by three sources of energy 1 Solar energy 2 Tidal forces from Sun and Moon s gravity 3 Earth s internal heat left over from the creation 39Atmosphere IS powerEd by able 92 The Earth s Energy Sources solar energy l a T uniting lnlnlrrtltl Motion of water in oceans Solar energy tidal forces Ocean is powered by solar lakes mas e n e a nd Motion of the atmosphere Solar energy Reshaping of surface Earth s internal heat Life Solar energy a few species oLand is powered the that live on the ocean floor make use of the Earth s internal heat The Greenhouse Effect Greenhouse effect greenhouse gases in the atmosphere trap the infrared radiation emitted from the Earth s surface and raise the temperature of the atm osp he re 1 Sunlight arrives 2 39 of sunlight is 6 Remaining at the Earth reflected by clouds 4 infrared and the surface 1 radiation quotleaksquot 39 l 1 l 7 into space 5 Some infrared radiation is trapped by i i atmosphere 3 Sunlight if heating both that is not 27quot atm sphere reflected g and surface is absorbed i by surfafe 4 Heated surface emits heating It infrared radiation 7 quotSurfEe U 7 The Greenhouse Effect The Earth s surface is directly heated by the radiation from the Sun because the atmosphere is almost transparent to the visible light The Earth s surface emits infrared radation The 002 gas and H20 water vapor so called greenhouse gases in the atmosphere strongly absorb the infrared radiation thus trap the solar energy The greenhouse effect raises the Earth s surface temperature by 41 C The average actual surface temperature is 14 C If no greenhouse effect the calculated surface temperature would be about 27 C Earth s interior structure Earth has a layered internal structure due to chemical differentiation process in the early time When Earth was newly formed it was molten throughout its volume due to the heat from impact Dense materials such as iron sank toward the center Lowdensity materials rose toward the surface Liquid iron outer core Less dense 50Id Iron material Inner core Mantle Crust V r 39 x 139 irnn null n lllc LEIIch I I floated upward bAsa 39 39 Hm E L a u mu that we see today Earth s interior structure Presentday Earth has three layers crust mantle and core Crust 5 km to 35 km deep solid made of relatively light siliconrich minerals Mantle 2900 km deep solid made of relatively heavy iron rich minerals Core 2900 km 6400 km deep made of pure iron Outer core 2900 km 5100 km deep liquid Inner core 5100 km 6400 km deep solid Crust solid 0 5 under oceans 6343 6378 3500 0 35 under continents Mantle solid from bottom of crust to 2900 3500 6343 3500 5500 Outer core liquid 2900 5100 1300 3500 10000 12000 Inner core solid 5100a6400 04300 13000 Earth s interior structure Earth s internal structure is deduced by studying how the seismic waves produced by Earthquakes travel through the Earth s interior Seismic waves refract or change the path as they pass through different part of the Earth s interior S waves Shadow zone P waves neither P waves nor 5 waves Both P waves reach here and S waves reach here Only P waves reach here Earthquake Both P waves and S waves reach here Shadow ZOI39IE Earth s interior structure From surface to center m M quotI temperature as well as pressure 9 233 4 rises steadily from 14 C to 5000 C 4000 The state depends on the actual temperature relative to the melting temperature Melting temperature is determined by chemical composition and 1000 pressure The mantle is primarily solid because I n I I r 0 1000 2000 3000 4000 5000 6000 the temperature there IS lower than Depthkml i 39 I l the melting pomt 5000 soon 4o39oo so39oo 20100 10100 9 D39t f t fE thk I The outer core IS IIqUId because the mmquotquot9quot r m 3000 re 2000 Temperature C temperature there is higher than the melting point Plate Tectonics The world map indicates that the continents would fit rather snugly against each other oAlfred Wegener in 1915 suggested the idea of continental drif A continents have originally been a single gigantic supercontinent called Pangaea meaning all lands Plate Tectonics About 200 million year ago almost all continents were merged into a single supercontinent called Pangaea a 237 million years ago the supercontinent Pangaea A 50quot Africa z merlta i I GONDWANA Australia Antarctica quot Plate Tectonics Pangaea first split into two smaller continents Laurasia in the north and Gondwana in the south b 152 million years ago the breakup ofPangaea 39 39 North 7 V 39v 39 K x W I V i k 5 quotH 7 d3 Americ Antarctica Plate Tectonics The continental drifting speed is several cm per year For example at a rate of 3 cmyear over 200 million years the drifting distance is 6000 km c The continents today mtgen Jill i Ural Siberia Plate Tectonics Plate tectonics is caused by the internal heat of the Earth Asthenosphere is the upper levels of the mantle that are hot and soft enough to permit a plastic flow Internal heat causes convection flows in asthenosphere Molten material from asthenosphere wells up at oceanic rifts producing seafloor spreading and is returned to the asthenosphere in subduction zones As one end of a plate is subducted back into the asthenosphere it helps to pull the rest of the plate along At a rift between separating plates lava oozes upward and forms new crust Ocean floor Lithosphere continent Where plates colide deep oceanic trenches and mountain ranges are formed Plate Tectonics The Earth s crust and a small part of its upper mantle form a rigid layer called the lithosphere The lithosphere is divided into plates that move over the plastic layer called the asthenosphere in the upper mantle Most earthquakes occur where plates separate collide or rub together plate boundaries are identified by plotting earthquake epicenters EURASIAN H1 39 39 39 39 I v 0 50 km deep shallow focus 39 l I 4 I 39 quot quot quot Iquot 139rquotquot 50393 km deep quotwas r A N TA R c T I c 7quotQ x 39 0 gt300 km deep deep focus 39 quot33911 gt P LAT E I lquot Plate Tectonics The MidAtlantic Ridge Lava seeps up from the Earth s interior along a rift extends from Iceland to Antarctica The upwelling motion of lave forces the existing crusts apart causing seafloor spreading As a result South America and Africa are moving apart at a speed of 3 cm peryear Plate Tectonics The Himalayas Mountain The plates that carry India and China are Himalayas colliding Both plates are pushed r upward forming the highest mountains on the Earth Earth s Magnetosphere The motion of the liquid iron core of the Earth which carries electric currents generates magnetic fields This magnetic field produces a magnetosphere that surrounds the Earth Magnetosphere the region of space around a planet in which the motion of charged particles is dominated by the planet s magnetic field Solar wind a continuous flow of charged particles mostly protons and electrons streaming out constantly from the Sun Near the Earth the solar wind speed is about 450 kms Earth s Magnetosphere Magnetosphere deflects most of the particles of the solar wind from entering the Earth s atmosphere thus protect the Earth from harmful particle radiation 100003 km Earth s Magnetosphere During the period of enhanced solar activity the magnetosphere may be overloaded with changed particles Charged particles leak through the magnetic field and move down collide with atoms in the upper atmosphere and cause the shimmering light display called aurora Earth s Atmosphere Composition The Earth s atmosphere differs from those of the other terrestrial planets in its chemical composition temperature profile and circulation pattern Composition of presentday 78 Nitrogen 21 Oxygen and 1 water vapor and carbon dioxide greenhouse gas The composition of atmosphere has evolved with time due to presence of living organims tille 91 Chemical Compositions of Three Planetary Atmospheres 11ii391317 Nitrogen NZ 35 7808 27 Oxygen 02 almost zero 2095 almost zero Carbon dioxide C02 965 0035 953 Water Vapor H20 0003 about 1 003 Other gases almost zero almost zero 2 Earth s Atmosphere Composition During the early time the Earth s atmosphere is primarily 0021 produced by volcanic eruptions The appearance of life radically transformed the atmosphere Photosynthesis A chemical process by plants that converts energy from sunlight into chemical energy It consumes 002 and water and release oxygen 02 Over time 02 continues to increase and stablizes at 21 1oo 80 Pt t 3 First eukaryvtic Oldest rocks First land animals Origin ufland plants Origin of sexuality cells F39rs Originof mammals flowering mplants of First 3 vertebrates 9 SF First exoskeletons First metazuans Begin 02 growth I I 4643 I 2 Illllll I I I 186 4 2 1 Billions of years before the present Earth s Atmosphere Temperature Based on temperature profile the Earth s atmosphere is divided into layers called the troposphere stratosphere mesosphere and thermosphere Troposphere 0 12 km 15 Temperature decreases with increasing altitude because the sunlight heats the ground and upper part remains cool This temperature profile in troposphere causes a convection currents up and 0 80 6o 40 20 5 30 40 60 so 100 down resulting in all of the Temperature 0C Earth s weather 100 Thermosphere Altitude km gt U 0 Earth s Atmosphere Temperature Stratosphere 12 50 km Temperature increases with increasing altitude Temperature increases because an appreciable amount of ozone 03 in this layer direct absorb ultraviolet from the Sun This temperature profile does not allow any convection in the stratosphere Mesosphere temperature decreases again with increasing height because little ozone exists there Thermosphere temperature increases with altitude because the present of individual oxygen and nitrogen directly absorb extremely short ultraviolet light from the Sun Earth s Biosphere Biosphere the thin layer enveloping the Earth where all living organisms reside including The oceans The lowest few kilometers of the troposphere The crust to a depth of almost 3 kilometers Earth s Biosphere The Distribution of Plant Life Land colors designate vegetation dark green for the rain forests light green and gold for savannas and farmland and yellow for the deserts Ocean colors show that phytoplankton are most abundant in the red and orange areas and least abundant in the dark blue areas Earth s Biosphere Human population began to rise in late 1700s with the industrial revolution The rise accelerated in the 20th century thanks to medical and technological advances such as antibiotics 57 0 World population billions ed 010 560 A39D 560 1600 153900 zo39oo Year Human Population Earth s Biosphere Global warming a warming trend of global temperature in the past 140 years It is predicted to continue to rise It is partially due to the industrial release of greenhouse gas such as C02 by burning petroleum and coal relative 01961 1990 average Global surface air temperature Cl I39l39l I39I39l39Ill 1860 1880 1900 1920 1940 1960 1980 2000 m C02 concentration pp wwwwww w uumu on oooooo in N O 310 1955 1965 1975 1985 1995 2005 0 Changes in the Earth s average temperature Earth s Biosphere Ozone hole a region with an abnormally low concentration of ozone Ozone can be destroyed by industrial chemicals CFCs There has been worldwide increase in the number of deaths due to skin cancer caused by solar UV radiation Ozone abundance 100 200 300 400 500 October 1979 September 2003 ASTR 111 003 Fall 2007 Lecture 02 Sep 10 2007 Introduction To Modern Astronomy I Solar System Ch1 Astronomy and the Universe Introducing Astronomy Chap 1395 Ch2 Knowing the Heavens Ch3 Eclipses and the Motion of the Moon Planets and Moons Chap 73915 Ch4 Gravitation and the Waltz of the Planets Ch5 The Nature of Light Chap 16 Our Sun Ch6 Optics and Telescope Chap 28 Search for Extraterrestrial life Heavens Chapter Two Hawaii N20 Washington DC N38 Positional Astronomy Positional astronomy the study of the positions of objects in the sky and how these positions change It has roots in almost all ancient civilizations Nakedeye astronomy the sort that requires only human vision no telescope p41 The Sun Dagger at Chaco Canyon New Mexico Positional Astronomy Position of stars in the heaven forming consternations Path of Sun Moon and Planets forming zodiac band Flu 71 Constellations From the Latin for group of stars o 39 Bellatrix 240Iy 0 39Mintaka ERlDANUS 39 Rigel 775Iy ORON the Hunter Betelgeuse the armpit Mintaka the belt Constellations we ENTERS Ram the Bull I I the Twins Zodlac Constellations Crab 12 In total along the ecliptic path union the Virgin the Balance Lhe Scorpion the Archer the Goat the Fish Constellations On modern star charts the entire sky is divided into 88 constellations Starts in the same constellation only appear to be close because they are in nearly the same direction as seen from Earth However most stars in a constellation are nowhere near one another in real 3D distance North Star Polaris Visibe anywhere in the northern hemisphere The position of the extended Earth rotation axis into the sky The north direction can be found by drawing a line straight down to the horizon URSA MINOR quotLittle Dipperquot BoorEs 39 quot Polaris Arcturus quot i a quotNorth Sta r Z URSA MAJOR quotBig Dipperquot Western horizon Summer Triangle Three of the brightest stars in the summer evening in the northern hemisphere V o vltltai l I quotNorthern Cro39ss AQUILA 0 atquot quot DELPHINUS Eastern horizon Winter Triangle Three of the brightest stars in the winter evening in the northern hemisphere CANIS MINOR Procyon Southern horizon Diurnal Motion of Stars Stars appear to rise in the east slowly rotate about the earth and set in the west over the night This diurnal or daily motion of the stars is actually caused by the rotation of the earth It has a eriod of one da exactly 23 hr 56 min FLASH 0204DiurnalMotionswf Diurnal Motion of Stars Illuminated Dark Rotation of day side Ifquot night side I he Earth I 39 Andromeda I gt r Light from L t Iquot the sun 5 1 1 gt quot gt L f Andromeda is Rotation of 5 overhead as seen the Earth 7 erson in from California Pena l 3 Cygnus i5 overhead as cal39fOrma calibmla seen from California idnisl 800 PM local time local time K ngnus a Earl39h as seen from above The North POIG b 4 hours onesixth of a complete rotation later View from the vantage point of above the North Pole Earth rotates counterClockwise from west to east View from the Earth Stars rotate from east to west Yearly Motion of Stars when viewed at the same time eg midnight at the same location on the Earth the stars appear to slowly shift in position throughout the year If you follow a particular star on successive evenings you will find that it rises approximately 4 minutes earlier each night Or 2 hours earlier each month The star pattern in the evening eg midnight will be exactly the same after one year The shift is due to the orbital motion of the Earth around the Sun Yearly Motion of Stars Earth s orbit 0 Perseus I I 1 Earth in November a Light from the Sun This shift motion has a period of exactly one year Earth in September gt Light from the Sun Light from The 5quot Orbital motion of the Earth Celestial Sphere Celestial sphere an imaginary sphere that all starts are fixed on its surface In the sphere all stars are assumed in the same distance The Earth is stationary and at the center of the sphere Note that it is an imaginary object that has no basis in physical reality However it is a model that remains to be very useful for positional astronomy It represents well the diurnal motion by assuming the whole sphere rotates in a daily basis It also helps to track and visualize the patterns of motion of the Sun and planets across the sky background Celestial Sphere Celestial equator mg Earth s equator projected out Celes alsplm into space divides the sky into northern and southern hemispheres A miliiima kwte Celestia poles Earth s axis of rotation intersect the celestial sphere North celestial pole South celestial pole Lemma pole Polaris is less than 1 away from the north 1 celestial pole CeestiaSphereswf Celestial Sphere The celestial sphere appears tipped viewed by an observer Zenith Point in the sky directly overhead At any time observer can see only half of the celestial sphere divided by the local ho zon At 35 north latitude the north celestial pole is 350 above the northern horizon 39The Sta rS Close to n O the south celestial pole is 35 below the southern horizon pole never sets Celestial Sphere The tilt of the celestial sphere the apparent 1 a A motion of stars at different latitudes 0202ApparentMotionswf a At iddle northern latitudes c At the equator Celestial Sphere coordinates tools in Box 21 Celestial coordinates Denote position of objects in the celestial sphere Right Ascension O24h Corresponds to longitude Starting from Vernal Equinox the point where the Sun s path crosses the celestial equator in late March U I Declination 90 90 deg t L 22 Corresponds to latitude 39 Starting from the equator elestial sphere Vernal equinox Seasons Spring Summer Autumn Winter A year or 365 days is the period Summer is hotter Winter is cooler In summer the day time is longer than 12 hours In winter the day time is shorter than 12 hours Seasons are opposite in the two hemispheres Seasons the Cause Seasons are caused by the tilt of Earth s axis rotation The Earth s axis is tilted about 2312 away from the perpendicular to the plane of the Earth s orbit The Earth maintains this tilt as it orbits the Sun Spring in the northern hemisphere autumn In the southern hemisphere North Pole Winter in the northern hemisphere summer in the southern hemisphere North pole South pole North pole 23 South pole Summer in the northern hemisphere winter in the southern hemisphere ECI39Ptquot south pole Autumn in the northern hemisphere spring in the southern hemisphere FLASEEU 0205TheSeasonsswf Seasons the Cause Why is the summer hot Because 1 the surface receives the Sun s light or heat longer the hemisphere is tilted toward the Sun As the Earth spins on its axis the surface spends more than 12 hours in the sunlight The days are long and the nights are short 2 The Sunlight heats the surface more efficiently the Sun is high in the sky sunlight strikes the ground at a nearly perpendicular angle that heats the ground efficiently Seasons the Cause cont When the Sun is high in the summer the sunlight is more concentrated and thus increases the heating In the winter the Sun is lower the sunlight is less concentrated and thus reduces the heating l 7 r l l The Sun is high L l l in the midday 1 summer sk l y x 1 l The Sun is low in the l midday winter sky 53quotquot w 4 773 a l so the same shaft of l sunlight is spread out 33a EITaE off l sunlight is l concentrated onto overa larger area and l l a small areawhich l less heating of the heats the ground 1 ground takes place effectively and 39 39 39 makes the days warm l 39 a The Sun in summer 3 The Sun in winter The Sun s Path The seasons are formerly determined by the positions of the Sun in the celestial sphere How to declare the beginning of a season Why is spring always starting on March 21 Ecliptic the plane of the Earth annual orbit around the Sun also the plane of the Sun s annual orbit in the celestial sphere 5 to us the Sun travels around the celestial sphere once a year a in reality the Earth orbits the Sun ence a ymr b ll appear The Sun s Path The ecliptic plane is inclined to the equatorial plane in the celestial sphere by 235 because of the tilt of the rotational axis of the Earth North celestial poJ n diptic Autumnal equinox 7 RSummer solstice Winter solsticek39s N Celestialequator I I Vernalequinox South celestial pole The Sun s Path Equinoxesz the points that the ecliptic path and the celestial equator intersect There are only two points thus two equinoxes Vernal equinox the Sun crosses northward across the celestial equator Occurs on about March 21 Marks beginning of spring in northern hemisphere Autumnal equinox the Sun crosses southward across the celestial equator Occurs on about Sep 22 Marks beginning of autumn in northern hemisphere At equinoxes the day time is exactly 12 hours The Sun s Path Summer Solstice the point on the ecliptic farthest north of the celestial equator Occurs on about June 21 Marks the beginning of summer in the northern hemisphere the day time is the longest Winter Solstice the point on the ecliptic farthest south of the celestial equator Occurs on about Dec 21 marks the beginning of Winter in the northern hemisphere The day time is the shortest The Sun s Path The daily path Z nitquot in different Ce39estia39 days of the Nat year In summer more than 12 hours In winter less than 12 hours In winter in the northern hemisphere the Sun rises in i the southeast and sets in the southwest 7 the northern hemisphere the Sun rises in the northeast and sets in the northwest the first aangpringi and the first day of fall the Sun rises precisely in the east The Sun s Path The Sun is above the horizon continuously in the region close to the poles during the summer 1140 RM 340 AM 1240 AM 240 AM 140 AM Precession Besides the daily rotation and yearly orbital motion the Earth also undergoes a long term precession The precession is a slow conical motion of the Earth s axis of rotation about the perpendicular to the plane of the orbit It is caused by the gravitational pull of the Sun and the Moon on the Earth s equatorial bulge To 1 of omion s damn Emir mulion 0w 5minan pull arms Moon Precession The consequence is that the north celestial pole slowly changes and traces out a circle among the northern constellations The circle has a radial size of 235 The period is 26000 years After 12000 years the north pole will be Vega 39m 153000 7 Path of non lilastial CORONA quot BOREALIS 9 H A 39 39 39URSA MAJORquot Timekeeping A day is the interval between the successive upper meridian transits of the Sun Meridian the northsouth circle on the celestial sphere that passes through the local zenith and both celestial poles Noon defined as the Sun crosses the upper meridian Midnight cross the lower meridian Zen h Note meridian circle zenith and noon are all local in other words they depend on the location on the Earth I I S Honzon 2 m39 W Timekeepi ng However the Sun is a poor timekeeper An apparent solar day varies over the course of the year The Earth s orbit is not a perfect circle The Earth moves faster when it is near the Sun in January making the clay longer The ecliptic path is tilted with respect to the celestial equator making the projected progress along the equator varies during the year The apparent solar day may vary up to 15 minutes WM orbit Earth39s during January Earth39s The Earth novels different Jlxmnces in the same at Unit at LJl LTL Ut elhpucal Orbll a A month39s motion of the Earth alum its orbit lmmlrll part at in North celestial pole Ecliptic Equal 5mm he Sun Jhmk pr0ecr omo me celesnal cqlmmr as Airmen distances Celestial equator A dav39s motion of the Sun along the ecliDtic Timekeeping A modern day is the mean solar day defined by the interval between successive upper meridian transit of the mean sun Mean Sun is the imaginary sun that travels at a uniform rate the average of all the apparent days over one year along the celestial equator Mean Sun produces a uniform mean solar day of exactly 24 hours Ordinary watches and clocks measure mean solar time Time Zone and Universal Time For convenience of people and making the time meaningful the Earth is divided into 24 time zones centered on 15 intervals of longitude around the globe UT universal time for convenience of aviator and sailors who regularly travel across time zones It is always the time in the zone that includes Greenwich England PACIFIC Calendar and Leap Years Calendar is required to be based on tropical year which is equal to the time needed for the Sun to return to the vernal equinox on the celestial sphere so that the first days of seasons fall on the same date each year A tropical year is 3652422 mean solar day or 365 d 5 h 48 m 46 s Julius Caesar s calendar assuming year36525 days Leap year the offset of 025 dayyear adds one more day in every 4 years However the off of 11 m 14 5 adds three days every four centuries Gregory Calendar Pope Gregory XIII current calendar assuming year 3652425 day Dropped ten days from Oct 4 1582 to Oct 15 1582 brought the spring Sun passes the vernal equinox back to March 21 Leap year every four years and the year divisible by 4 Only century years divisible by 400 should be leap years The error is only one day in every 3300 years llZT l 5 r l Sidereal time a preferred time by astronomers It is based on the position of the star not the Sun It makes easier to track astronomical objects A sidereal day is the time between successive upper meridian passages of the vernal equinox 23h 56m Earth moves about 1quot around its orbit in one so Earth must make a complete Local solar noon on March 21 is at this location to local solar noon on March 22 Earth on March 22 v Earth on March 21 A sidereal day the time takes the Earth rotate exactly 360 A solar day the time takes the Earth rotate 360 plus 1 or 4 more min of rotation to make up the Sun s shift caused by orbital motion FLASH 0203SideralTimeswf Final Notes on Chap 2 All sections 21 to 28 are covered Two tool boxes Box 21 and 22 are covered The Nature of Light ASTR 111 003 Lecture 05 Oct 01 2007 Fall 2007 Introduction To Modern Astronomy I Solar System Introducing Astronomy chap 16 Planets and Moons chap 715 Chap 16 Our Sun Chap 28 Search for Extraterrestrial life Ch1 Astronomy and the Universe Ch2 Knowing the Heavens Ch3 Eclipses and the Motion of the Moon Ch4 Gravitation and the Waltz of the Planets Ch5 The Nature of Light Ch6 Optics and Telescope Speed of Light The speed of light in the vacuum C 299792458 kms 0r C 300 X 105 kms 300 X 108 ms It takes the light 500 seconds traveling 1 AU It takes the light 42 years to the nearest star Proxima Centauri Milky way diameter 100000 lys Speed of Light In 1676 Danish astronomer Olaus Romer discovered that the exact time of eclipses of Jupiter s moons depended on the distance of Jupiter to Earth The variation is about 166 minutes or 1000 seconds Earth This happens because it takes varying times for light to travel the varying distance between Earth and Jupiter varying by up to 2 AU Earth near Jupiter we observe eclipses of Jupiter39s moons earlier than expected Earth far from Jupiter we observe eclipses of Jupiter39s moons later than expected Electromagnetic Waves Newton in 1670 found that the White light from the Sun is composed of light of different color or spectrum White light A prism breaks light into its component colors or spectrum Wavelengths The spectrum of different falls on a screen colors of light 700 um l l 600 nm 500 um 400nm White light First prism breaks light into its spectrum Screen lets only one color pass through Second prism bends light but does not change its color Electromagnetic Waves Young s DoubleSlit Experiment in 1801 indicated light behaved as a wave The alternating black and bright bands appearing on the screen is analogous to the water waves that pass through a barrier with two openings Bright bands where light waves from the Slits t rt f h th gtlt Crosses W0 5 l S rein orce eac 0 er Loca ons where crests screen overlap crests th waves and the waves l l l reinforce ance39 Dark bands where light waves from the Water waves emerge from openings in a barrier two slits cancel each other Electromagnetic Waves Magnetic field Electric field Direction of propagation lt Wavelength A The nature of light is electromagnetic radiation 0 In the 18603 James Clerk Maxwell succeeded in describing all the basic properties of electricity and magnetism in four equations the Maxwell equations of electromagnetism Maxwell showed that electric and magnetic eld should travel in space in the form of waves at a speed of 30 X 105 kms Electromagnetic Waves w23h Visible light falls in the 400 to 700 10395 nm 104m 67222 nm range 103 1022 In the order of decreas1ng 1 quotquot1quot XL wavelength 1 quotm quot Ultraviolet 400 nn 10nm radiation 33 Radlo waves gt 10 cm 100 nm Yellow Microwave 1 mm 10 cm 103 nm 1 4m Orange 10 um VI5Ible light Red 1mm V Klnfrared m quotm Infrared 700 nm 1mm 1 22 quot mquot 1t quota mquot Visible light 400 nm 700 nm mm 1 cm Micrmlaves quotquotquot quot n Ultraviolet 10 nm 400 nm 100 cm 1 m 10mquot Xrays 001 nm 10 nm 100 m quot Radio waves 1000m1km Gamma rays lt 001 nm 10 km Longest 100 km wavelength Electromagnetic Waves 7 a 3 i r r 31Mabile phane b Mimwave nven39 c TV remote in Tanning booth e Medial imagng radio waves microwaves infrared iigit violet light x rays Uses of Nonvisible Elect magnetic Radiation Electromagnetic Waves 3 V xi v Frequency in Hz 9t Wavelength in meter 0 Speed oflight 3 X 108 ms Example FM radio eg 1035 MHZ WTOP station gt 9 290 m Visible light eg red 700 nm gt v 429 X 1014 Hz Blackbody Radiation Heated iron bar as the temperature increases 7 The bar glows more brightly 7 The color of the bar also changes 1a Hotzglcws deep red b Hotter glows orange c Even hotter glows yellow Blackbody Radiation Blackbody curve the intensities of radiation emitted at various wavelengths by a blackbody at a given temperature The higher the temperature the shorter the peak wavelength The higher the temperature the higher the intensity Intensity gt Visible light E o 500 1000 2000 3000 Wavelength nm gt Blackbody curve Blackbody Radiation A blackbody is a hypothetical object that is a perfect absorber of electromagnetic radiation at all wavelengths The radiation of a blackbody is entirely the result of its temperature A blackbody does not reflect any light at all Most dense objects can be regarded as a blackbody eg a star a planet a human body but not a thin cloud a layer of thin gas lights get through Intensity X m z nm I Blackbody Radiation The Sun s radiation is remarkably close to that from a blackbody at a temperature of 5800 K 22 5 11quot W 20 1V3 1V5 14 39 Sulidcum 1392 1 u 1 5 iquot Sm nashcdcum 10 I I 03 5 I 0V6 39 quot 04 1 I 4 02 39 I 00 39 I 39 1000 1500 2000 2500 Wavelength mm Box 51 Temperature Scales Temperature in unit of Kelvin is often used in physics TK TC 273 TF 18 TC32 Kelvin Celsius Fahrenheit 6 m Sun s core temperature 580 Sun s surface temperature Boiling point of water Freezing point of water Absolute zero Zero Kelvin is the absolute minimum of all temperatures Wien s Law Wien s law states that the wavelength of maximum emission of a blackbody is inversely proportional to the Kelvin temperature of the object f Il t iil E m mm Jam wavelength if maximum emissiun of the nhjeet in meters 3 T temperature it39ll the uhjeet in kelvinsi For example TheSun A 500nm9T5800K 9 max Human body at 100 F What is AmaX BOX 52 Wien s Law Sirius the brightest star also called dog star in Canis Major in the night sky has a surface temperature of 10000 K Find the wavelength at which Sirius emits most intensely StefanBoltzmann Law The StefanBoltzmann law states that a blackbody radiates electromagnetic waves with a total energy flux F directly proportional to the fourth power of the Kelvin temperature Tof the object F039T4 F energy flux in joules per square meter of surface per second 6 StefanBoltzmann constant 567 X 10398 W m2 K4 T object s temperature in kelvins 1 J kinetic energy of a 2 kg mass at a speed of 1 ms 1 W 1 Js power F energy flux Jm2s flux BOX 52 StefanBoltzmann Law Sirius the brightest star also called dog star in Canis Major in the night sky has a surface temperature of 10000 K How does the energy flux from Sirius compare to the Sun s energy flux Dual properties of Light 1 wave and 2 particle Light is an electromagnetic radiation wave eg Young s double slit experiment Light is also a particlelike packet of energy A light packet is called photon The energy of photon is related to the wavelength of light Light has a dual personality it behaves as a stream of particles like photons but each photon has wavelike properties Dual properties of Light Planck s law relates the energy of a photon to its wavelength frequency E energy of a photon h Planck s constant b5 6625 X 10 34 J S i A c speed of light 9L wavelength of light Energy of photon is inversely proportional to the wavelength of light Example 633nm redlight photon E 314 X 10 19 J or E 196 eV eV electron volt a small energy unit 1602 X 10 19 J Box 53 Planck s Law The barcode scanners used at supermarket emit orangered light of wavelength 633 nm and consume a power 1 mW Calculate how many photons are emitted by one such scannerpersecond Spectral Lines The Sun s spectrum in addition to the rainbowcolored continuous spectrum it contains hundreds of ne dark lines called spectral lines Fraunhofer 1814 A perfect blackbody would produce a smooth continuous spectrum With no dark lines I l I ll I l l I I 1 II I II I II I I ll I l l I II I I ll 1 ll III III II ll l l l l IIlI I E III II III Illl I lll ll II II ll III I ll II II l l lllll III ll I III lll ll l lll I l L lIlL IL L I lll ll III I III IlIIIIII Ill 1 l Ill I I II II I l Ill l ll l l l lll II III lllllllll ll l llll l ll l ll l lll l I ll l lllll l l l ll l l l I ll 39ll I II llll III I II I lll Illll ll ll l ll l l l l II II Illl I 39l i l39 I l The Sun s Spectrum quot39quotquot r 7 Spectral Lines Bright spectrum lines can be seen when a chemical substance is heated and valoprized Kirchhoff 1850 1 Add a chemical substance to a flame 2 Send light from 3 Bright lines in the the flame through spectrum show that a narrow slit then the substance emits through a prism light at specific wavelengths only Spectral Lines Helium He Hydrogen H2 Klypton Kr Merculy Hg Neon Ne Water Vapor H20 Xenon Xe Each chemical element has its own unique set of spectral lines Kirchhoff s Laws on Spectra Three different spectra continuous spectrum emissionline spectrum and absorption line spectrum Hot blackbody b ABSORPTION LINE SPECTRUM atoms in gas cloud absorb light of certain specific wavelengths producing dark lines in spectrum a CONTINUOUS SPECTRUM c EMISSION LINE SPECTRUM blackbody emits light at all atoms in gas cloud re emit absorbed wavelengths light energy at the same wavelengths at which they absorbed it Kirchhoff s Laws on Spectra Law 1 Continuous spectrum a hot opaque body such as a perfect blackbody produce a continuous spectrum a complete rainbow of colors Without any spectral line Law 2 emission line spectrum a hot transparent gas produces an emission line spectrum a series of bright spectral lines against a dark background Law 3 absorption line spectrum a relatively cool transparent gas in front of a source of a continuous spectrum produces an absorption line spectrum a series of dark spectral lines amongst the colors of the continuous spectrum Further the dark lines of a particular gas occur at exactly the same wavelength as the bright lines of that same gas Structure of Atom An atom consists of a small dense nucleus at the center surrounded by electrons which orbit the nucleus The nucleus contains more than 99 of the mass of an atom but concentrates in an extremely small volume A nucleus contains two types of particles protons and neutrons A proton has a positive electric change equal and Electrons opposite to that of an electron A neutron about the same f h Nucleus has mass 0 a proton as no pmmmhown electric Charge in red and neutrons shown in blue An atom has no net electric charge Box 55 P108 Periodic Table Periodic Table 0 the Elements Atomic number the number of protons in an atom s nucleus and thus the number of surrounding electrons determines a particular element The same element may have different numbers of neutrons in its nucleus which are called isotopes Bohr s Model of Atom Electrons occupy only certain orbits or energy levels When an electron jumps from one orbit to Bfg39fjfbgs another it emits or quot1 39 absorbs a photon of quot2 appropriate energy quot3 n 4 etc The energy of the photon equals the difference in energy BOhr S Model of between the two orbits Hydrogen Atom Bohr s Model of Atom Absorption is produced when electron absorbs incoming photon and jumps from a lower orbit to a higher orbit Emission is produced when electron jumps from a higher orbit to a lower orbit and emits a photon of the same energy Incoming photon A 6563 nm Emitted photon 0502AbsorptionPhotonswf a Atom absorbs a 6563um b Electron falls from the n 3 photon absorbed energy causes orbit to the n 2 orbit energy lost electron tojump from the n 2 orbit by atom goes into emitting a up to the n 3 orbit 6563nm photon Bohr s Model of Atom The strongest hydrogen spectral line from the Sun Ha line at 656 nm is caused n by electrontransition between n3 orbit and n20rbit Balmer series lines between n2 orbit and higher orbits n3 4 5 Lyman series lines between nl orbit and higher orbits n2 n3 n4 UV Paschen series lines between n3 orbit and higher orbits n4 n5 n6 IR 3 lVisible andI Ultraviolet Ultravioleq Infrared 136 eV 128 eV 121 eV series 102 eV Balmer series Emission Ground state 0 eV Lyman series Doppler Effect Doppler effect the wavelength of light is affected by motion between the light source and an observer Wave crest 1 emitted when light source was at 51 Wave crest 2 emitted when light source was at 52 1 Wave crests 3 and 4 emitted when light source was at 3 and S4 respectively Motion of Ilght source This observer sees redshift This observer sees blueshift Doppler Effect Red Shift The object is moving away from the observer the line is shifted toward the longer wavelength Blue Shift The object is moving towards the observer the line is shifted toward the shorter wavelength AMKO vc AA wavelength shift k0 wavelength if source is not moving v velocity of source 0 speed of light Questions What if the object s motion perpendicular to our line of sight Box 56 Doppler Effect In the spectrum of the star Vega the prominent Hor spectra line of hydorgen has a wavelength A 656255 nm At laboratory this line has a wavelength A0 656285 nm What can we conclude about the motion of Vega Final Notes on Chap 5 There are 9 sections All section are covered ASTR 111 003 Fall 2006 Lecture 10 Nov 06 2006 Introduction To Modern Astronomy Ch7 Comparative Planetology I Introducing Astronomy Ch8 Comparative Planetology II chap 16 Ch9 The Living Earth Ch10 Our Barren Moon Chll SunScorched Mercury Planets and moons Ch12 Cloudcovered Venus chap 717 Ch13 Red Planet Mars Ch14 Jupiter and Saturn ChlS Satellites of Jup amp Saturn Chl6 Outer World Ch17 Vagabonds of Solar System Guiding Questions Is the Moon completely covered with craters Has there been any exploration of the Moon since the Apollo program in the 1970s Does the Moon s interior have a similar structure to the interior of the Earth How do Moon rocks compare to rocks found on the Earth skip 104 How did the Moon form Moon Data Moon s Surface The moon has no atmosphere because its gravity is too small to retain any atmosphere The moon s surface features Craters Everywhere Terrae mean land the lightcolored area highlands on the Moon Maria mean sea the dark area 0 39 39 Lunar low lying plains highlands Moon s Surface Craters V 39 Caused by impacts from I H space debris 39 quot Everywhere no evidence of plate tectonic activity on the Moon Moon is too small to retain internal heat Moon s Surface Ma a plains of remains of huge lava flow dark color due to the color of solidified lava Fewer craters on a mare than the surrounding highlands Hence mare formed relatively young Mare basin was caused by impacts of very large meteoroids or asteroids Marezfewer rate hence relatively youquot cred terrain old produced this crater Manned exploration of the Moon From 1969 to 1972 12 astronauts walked on the Moon through 6 successful manned landings July 21 amp 256 UTC Armstrong put his left foot on the surface and spoke That s one small step for a man one giant leap for mankind Manned exploration of the Moon Much of our knowledge about the Moon has come from human exploration and from observations by unmanned spacecraft About 400 kg of lunar materials have been brought back by Apollo astronauts Seismic equipment have been put on the Moon to detect moonquakes and deduce the structure of the moon s interior Mirrors have been put on the Moon to measure the accurate EarthMoon distance using Laser light NASA Return to Moon plan Send 4 astronauts back to Moon in 2018 Build a large scale Moon base in the next 25 years Moon s Internal Structure Like the Earth the Moon has crust mantle and core Core is ironrich about 700 km in diameter Core is small no global magnetic field Moon s solid lithsophere is about 800 km thick In contrast the Earth s lithosphere is only 50 km thick Therefore Moon has no plate tectonics Solid lithosphere i Ironrich core A Plastic F il 1000 km asthenosphere Formation of the Moon The collisionalejection theory holds that the protoEarth was struck by a Marssized protoplanet debris from this collision coalesced to form the Moon and the giant impact quickly propelled a shower of debris from both the impacter During middle to late stages of Earth s and Earth into space accretionabout 45 billion years ago a Mars sized body impacted the Earth 0 42 minafter impact 39 125 min and the Moon aggregated from the debris Ancient moon rocks brought back by the Apollo astronauts support this impact hypothesis Formation of the Moon The collisionalejection theory explains Low density of Moon Small core of Moon Because the Earth s iron has sunk to its center due to chemical differentiation little iron would have been ejected and m giam impacz quixkly propelled a shower of debris mm bath the impacler and Earth inn 5pm Tidal Forces The Earth s tidal force on the Moon produces the synchronous rotation of the Moon The Moon s tidal force on the Earth slows down the Earth s rotation through the friction between Earth and its bulged oceans 0002 sec per century 1The Moon s tidal forces 2 Friction between the spinning elongate Earth s oceans along Earth and its oceans drags the an Earth Moon line tidal bulge about 10 ahead of alignment with the moon 4The tidal bulge on the side nearest the Moon exerts a small forward force on the Moon making it spiral slowly away from Earth 3 Friction between Earth and its oceans also makes the Earth rotate more slowly increasing the length of the day ASTR 111 003 Fall 2006 Lecture 03 Sep 18 2006 Introduction To Modern Astronomy Ch1 Astronomy and the Universe Ch2 Knowing the Heavens Introducing Astronomy chap 16 Ch3 Eclipses and the Motion of the Moon Ch4 Gravitation and Planets and Moons the Waltz of the Planets chap 717 Ch5 The Nature of Light Ch6 Optics and Telescope Guiding Questions Why does the Moon go through phases Is there such a thing as the dark side of the Moon What is the difference between a lunar eclipse and a solar eclipse How often do lunar eclipses happen When one is taking place where do you have to be to see it How often do solar eclipses happen Why are they visible only from certain special locations on Earth How did ancient astronomers deduce the sizes of the Earth the Moon and the Sun The phases of the Moon The cycle of 9New 9 Waxing Crescent 9 First Quarter 9 Waxing Moon39sorbit Gibbous 9 Full 9 Waning Gibbous 39 35113 9 I VJ moon Quarter 9 Waning Waning Crescent 9 quot moon 9 New The phases of the Moon causes The phases of the Moon occur because we see the varying amount of the illuminated half of the Moon as the Moon orbits around the Earth light from the Moon is actually reflected sunlight At any moment the Sun illuminates one half of the Moon A new moon occurs when the Moon is between the Sun and the Earth A full moon occurs when the Moon and the Sun are on the opposite side of the Earth Synchronous Rotation of Moon Observations show that the Moon always keeps the same hemisphere or face toward the Earth Synchronous rotation the Moon makes one rotation in exactly the same time that it makes one orbit around the Earth Thus we only see the same face ll 19 M n did not l le39 In fact the Moon does rotate we WM see aquot s39des the M n and we see only one face of the Moon Both craters visible Moon 5 arm Moon39s orbit Earth Blue crater Red crater visible visible D Light from 5quot from Earth from Earth red crater blue crater not visible not visible At all points In the orbit the red crater is visible from Ear ut t e In crater is not Light from Sun Both craters visible Synodic Month and Sidereal Month Synodic month or lunar month the Moon completes one cycle of phases or one complete orbit around the Earth with respect to the Sun averaging 2953 days Sidereal month the Moon completes one orbit around the Earth with respect to the stars averaging 2732 days The synodic month is longer because After the Moon travels 360 along its orbit around the Earth the Earth has also traveled about 27 along its orbit around the Sun To complete a cycle of phases the Moon must travel the additional 27 along its orbit around the Earth which takes about 2 days more Synodic Month and Sidereal Month The synodic month is longer because After the Moon travels 360 along its orbit around the Earth sidereal month the Earth has also traveled about 27 along its orbit around the Sun To distant constellation To complete a cycle of phases the Moon must travel the additional 27 along its orbit around the Earth which takes about 2 days more Earth39s orbit Solar and Lunar Eclipses k Solar and Lunar Eclipses Eclipses occur when the Sun Earth and Moon all happen to lie along a straight line the shadow of Earth Moon falls on the Moon Earth Lunar eclipse the Moon passes through the Earth s shadow The Earth is between the Sun and the Moon The Moon is at full phase The full moon appears quite dim during lunar eclipse Solar eclipse the Earth passes through the Moon s shadow The Moon is between the Sun and the Earth The Moon is at new phase The Sun sometimes fully disappears in the clear sky during the solar eclipse Eclipses do not Occur Every Month The plane of the Moon s orbit is tilted about 5 with respect to the plane of the Earth s orbit so called ecliptic plane At new and full phases the Sun Earth and Moon are often not along a straight line There are a few solar and lunar eclipses per year The maximum number combined in a single year is seven Plane of Earth39s orbit Moon s orbit plane of the ecliptic around the Earth Descending node x y 739 I 39Mggn s Earth39s orbit I I 39 7 around Ascendlng nodeJfYhe Sun 7 5 Line of nodes Plane of Moon39s orbit Eclipses and Line of Nodes Line of nodes the line along which the plane of the Moon s orbit intersects the plane of the Earth orbit Eclipses occur only when the Sun and Moon are both on the line of nodes Or when the Moon is on the ecliptic plane at the time of new phase or full hase Eclipse can occur FII i Earth39s orbit 0 7 eclipse possible Eclipse can occur possnble Line of nodes Lunarechses The Earth s shadow has two parts umbra and penumbra Umbra the darkest part of the shadow no portion of the Sun s surface can be seen form the Moon Penumbra ess dark of the shadow only part of the Sun is covered by the Earth Penumbra To partial eclipse
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