Chapter 1Chapter 1

• Light- years are used to measure Light- years are used to measure distances btwn. Celestial objectsdistances btwn. Celestial objects

• Celestial objects in descending order:Celestial objects in descending order:– UniverseUniverse– GalaxyGalaxy– NebulaNebula– EarthEarth

• Stars appears as smalls points of lightStars appears as smalls points of light• Alpha Centauri is the closest star to the Alpha Centauri is the closest star to the

sun (triple-star system)sun (triple-star system)– 4.3 light-years from Earth4.3 light-years from Earth

• Our sun is a single-star systemOur sun is a single-star system• Most stars are paired stars called BinariesMost stars are paired stars called Binaries– Binary stars are double-stars systemsBinary stars are double-stars systems

How to you think astronomers view stars?How to you think astronomers view stars?

Use Optical Telescopes (visible light)Use Optical Telescopes (visible light)

• Sirius/Dog Star, 8 light-years from EarthSirius/Dog Star, 8 light-years from Earth– Twice size of the sun, brightest star in skyTwice size of the sun, brightest star in sky

• Polaris/North Star, 700+ light-years Polaris/North Star, 700+ light-years – Important in navigationImportant in navigation– End of Little Dipper which is part of:End of Little Dipper which is part of:– Ursa Minor/Little Bear – constellation of stars Ursa Minor/Little Bear – constellation of stars

• Group of stars which people can see at one timeGroup of stars which people can see at one time• Imaginary figuresImaginary figures

– Ursa Major/Big Bear – 7 stars of this make up Ursa Major/Big Bear – 7 stars of this make up the Big Dipperthe Big Dipper

– 2 bright stars in the cup called Pointers → Polaris2 bright stars in the cup called Pointers → Polaris

• Orion, the Hunter – seen on clear Orion, the Hunter – seen on clear winter nightswinter nights– 2 bright stars in Orion:2 bright stars in Orion:• BetelgeuseBetelgeuse• RigelRigel

– Other close constellations are: Gemini, Other close constellations are: Gemini, Canus Major/Big Dog, Canis Minor/Little Canus Major/Big Dog, Canis Minor/Little DogDog

– Summer constellations: Summer constellations: • Scopius, Leo, Virgo Scopius, Leo, Virgo

• Nova – stars that suddenly increase Nova – stars that suddenly increase in brightness up to 100x for a short in brightness up to 100x for a short time then dimstime then dims– Almost all novas are binary systemsAlmost all novas are binary systems– Gases from companion stars strike the Gases from companion stars strike the

otherother• Nuclear explosion occurs creating: heat, Nuclear explosion occurs creating: heat,

light, & gaseslight, & gases

2 types of Star Clusters, appear as 1 star 2 types of Star Clusters, appear as 1 star from Earthfrom Earth

1.1. Open ClustersOpen Clusters• Not well organizedNot well organized• Hundreds of starsHundreds of stars• PleiadesPleiades

2.2. Globular ClustersGlobular Clusters• More commonMore common• Spherical, round shapeSpherical, round shape• 100,000+ stars100,000+ stars• HerculesHercules

• Huge clouds of dust that glow btwn Huge clouds of dust that glow btwn starsstars

• Birthplace of new stars Birthplace of new stars

• Galaxies – major features of the universeGalaxies – major features of the universe– Contain various groups of starsContain various groups of stars– Milky Way – we live inMilky Way – we live in– 100 billion + galaxies100 billion + galaxies

• 3 Types of Galaxies:3 Types of Galaxies:– Spiral – shaped like a pinwheelSpiral – shaped like a pinwheel

• AndromedaAndromeda• Milky WayMilky Way

– Elliptical – spherical to flat in shapeElliptical – spherical to flat in shape• Very little dust & gasVery little dust & gas• Older stars Older stars

– Irregular – no orderly shape, less commonIrregular – no orderly shape, less common• Large and Small Magellanic Clouds closest to the Large and Small Magellanic Clouds closest to the

Milky WaMilky Wayy

• Planet Earth is in the Milky WayPlanet Earth is in the Milky Way• Older stars found near the center/nucleus Older stars found near the center/nucleus – Dense in starsDense in stars– 20,000 light-years in diameter20,000 light-years in diameter

• Milky Way 100,000 light-years across and Milky Way 100,000 light-years across and 15,000 light-years thick15,000 light-years thick– 100,000 yrs to travel across @ speed of light100,000 yrs to travel across @ speed of light

• Sun located in pinwheel arm abt. 30,000 Sun located in pinwheel arm abt. 30,000 light-years from centerlight-years from center– One of the youngest stars in Milky WayOne of the youngest stars in Milky Way

• Spins counter clockwiseSpins counter clockwise– Takes 200 million yrs to rotate 1 time around Takes 200 million yrs to rotate 1 time around

center center

• Spectroscope – breaks up light Spectroscope – breaks up light into its characteristic colorsinto its characteristic colors– Light focused into a beam by a lens Light focused into a beam by a lens

then it passes through a prism then then it passes through a prism then broken into a band of colorsbroken into a band of colors

– Spectrum – band of colors formed Spectrum – band of colors formed when white light passes through a when white light passes through a prismprism

• All objects in the Universe are All objects in the Universe are movingmoving

• Spectroscopes help to determine Spectroscopes help to determine if galaxies or stars are moving if galaxies or stars are moving toward or away from Earthtoward or away from Earth

• As light strikes the prism of the As light strikes the prism of the spectroscope, prism bends the light spectroscope, prism bends the light according to the wavelength of each according to the wavelength of each colorcolor

• Stars moving fast toward Earth, light Stars moving fast toward Earth, light waves are compressedwaves are compressed– Blue end of spectrum known as Blue end of spectrum known as Blue ShiftBlue Shift

• Stars moving away from Earth, light Stars moving away from Earth, light waves are expandedwaves are expanded– Red end of spectrum known as Red end of spectrum known as Red ShiftRed Shift

• Doppler EffectDoppler Effect – apparent change in – apparent change in wavelengths of light moving toward or wavelengths of light moving toward or away from Earthaway from Earth

Big Bang TheoryBig Bang Theory states that the universe states that the universe began to expand with the explosion of began to expand with the explosion of concentrated matter and energy and has been concentrated matter and energy and has been expanding ever since.expanding ever since.

• Evidence Evidence – Expanding UniverseExpanding Universe– Background RadiationBackground Radiation

• Based on the assumptions that our present Based on the assumptions that our present universe is the result of expansion of matter universe is the result of expansion of matter from a single pointfrom a single point

• Astronomers believe that all galaxies are Astronomers believe that all galaxies are speeding away from the center of the Universespeeding away from the center of the Universe

• Gravity is the force that holds all galaxies Gravity is the force that holds all galaxies togethertogether

• Galaxies will continue to race Galaxies will continue to race outwardoutward

• Universe will continue to expandUniverse will continue to expand• Stars will eventually die, no more Stars will eventually die, no more

energyenergy• Future means everything may Future means everything may

eventually disappear in the universeeventually disappear in the universe

• Gravity will eventually pull all Gravity will eventually pull all galaxies back toward each othergalaxies back toward each other

• Blue shift will begin to be seeBlue shift will begin to be see• Matter & energy will again become Matter & energy will again become

packed into a small area and another packed into a small area and another big bang will occurbig bang will occur

• Quasars – most distance objects from Quasars – most distance objects from center of universecenter of universe– Abt 12 billion light-yrs from EarthAbt 12 billion light-yrs from Earth– Quasar stands for quasi-stellar radio Quasar stands for quasi-stellar radio

sourcessources• Gives off radio wavesGives off radio waves• Quasi Quasi = something like= something like• StellarStellar = star-like = star-like

• Quasars most mysterious objects in Quasars most mysterious objects in universe because they give off more universe because they give off more energy that 100+ galaxiesenergy that 100+ galaxies

• Light from a quasar 6 billion light-years Light from a quasar 6 billion light-years from Earth has traveled more that 6 from Earth has traveled more that 6 billion years to reach Earthbillion years to reach Earth

• 200 billion billion stars in the 200 billion billion stars in the UniverseUniverse

• Stars differ in many features:Stars differ in many features:– SizeSize– MassMass– ColorColor– TemperatureTemperature– BrightnessBrightness

• 5 main groups of size5 main groups of size1.1. Super Giant (largest)Super Giant (largest)

– 1000 times size of sun1000 times size of sun– Die quickly due to size Die quickly due to size

2.2. GiantGiant– 10 – 100 times size of sun10 – 100 times size of sun

3.3. Sun-sized (medium)Sun-sized (medium)– Most abundantMost abundant

4.4. White dwarfWhite dwarf– Smaller than EarthSmaller than Earth– Smallest white dwarf Van Mannen’s starSmallest white dwarf Van Mannen’s star

5.5. Neutron (smallest)Neutron (smallest)– Abt. 16 km Abt. 16 km

• Elements have “fingerprints” Elements have “fingerprints” – Creating certain color lines passed Creating certain color lines passed

through the spectroscope when burnedthrough the spectroscope when burned

• Hydrogen is most common element Hydrogen is most common element in starsin stars– 60-80% of total mass 60-80% of total mass

• Helium is 2Helium is 2ndnd most common element most common element• Both elements make up abt 96 -99 % Both elements make up abt 96 -99 %

of star’s massof star’s mass

• Star’s color help to determine surface Star’s color help to determine surface temperature of a startemperature of a star– Color is related to surface temperatureColor is related to surface temperature

• Surface temp. much lower that core Surface temp. much lower that core temp.temp.– Ex. SunEx. Sun

• Surface temperature abt 6000°CSurface temperature abt 6000°C• Core temperature abt. 15,000,000°CCore temperature abt. 15,000,000°C

– Hottest star abt. 50,000 °CHottest star abt. 50,000 °C– Coolest star abt. 3,000°CCoolest star abt. 3,000°C– Most stars somewhere in betweenMost stars somewhere in between

• Brightness depends on size of star, Brightness depends on size of star, surface temperature, distance from surface temperature, distance from EarthEarth

• Apparent MagnitudeApparent Magnitude – brightness of a – brightness of a star as it appears from Earthstar as it appears from Earth

• Absolute MagnitudeAbsolute Magnitude – amount of light – amount of light a star actually gives offa star actually gives off

• Most stars brightness is constantMost stars brightness is constant• Variable starsVariable stars brightness varies brightness varies– North Star/Polaris is a Pulsating Variable North Star/Polaris is a Pulsating Variable

star that changes size and brightness star that changes size and brightness

• Ejnar Hertzsprung – Danish astronomerEjnar Hertzsprung – Danish astronomer• Henry Norris Russell – American astronomerHenry Norris Russell – American astronomer• Both found that as absolute magnitude of Both found that as absolute magnitude of

stars increase the temperature of stars also stars increase the temperature of stars also increasesincreases

• Definite patterns formed called the Definite patterns formed called the Hertzsprung-Russell diagramHertzsprung-Russell diagram– Temperature plotted on horizontal axisTemperature plotted on horizontal axis– Absolute magnitude on vertical axisAbsolute magnitude on vertical axis

• Main-sequence stars are found in the upper Main-sequence stars are found in the upper left corner to the lower right cornerleft corner to the lower right corner

• Parallax – used to measure distance Parallax – used to measure distance to starsto stars– Refers to the apparent change in the Refers to the apparent change in the

position in the sky, Earth’s position not position in the sky, Earth’s position not movement of starmovement of star

• Brightness of the star is also used to Brightness of the star is also used to measure distancemeasure distance– Use apparent and absolute magnitude in Use apparent and absolute magnitude in

a complicated formulaa complicated formula

– Very strong gravitational forces in the Very strong gravitational forces in the core of starscore of stars

– Gravity pulls together atoms of Gravity pulls together atoms of Hydrogen gas so tightly they become Hydrogen gas so tightly they become fusedfused

• Nuclear FusionNuclear Fusion – hydrogen atoms – hydrogen atoms are fused to form helium atomsare fused to form helium atoms– Hydrogen changed into Helium at a Hydrogen changed into Helium at a

huge rate but a large amt of Hydrogen huge rate but a large amt of Hydrogen is lost. is lost. • Lost Hydrogen changed into energy in the Lost Hydrogen changed into energy in the

form of heat and lightform of heat and light– This is why stars shineThis is why stars shine

• Fusion within an aging red giant star Fusion within an aging red giant star causes temperature in the core of causes temperature in the core of the star to risethe star to rise

• Layers of the SunLayers of the Sun– Ball-shaped object made of extremely hot Ball-shaped object made of extremely hot

gasesgases– 4 main layers of sun4 main layers of sun

• Corona – outermost layer of sun’s atmosphereCorona – outermost layer of sun’s atmosphere• Chromosphere – 2Chromosphere – 2ndnd layer of sun’s atmosphere layer of sun’s atmosphere• Photosphere – innermost layer of sun’s Photosphere – innermost layer of sun’s

atmosphereatmosphere• Core – center of the sunCore – center of the sun

• Calm starCalm star• Prominences – solar storm, seen as huge Prominences – solar storm, seen as huge

bright arches/loops of gasbright arches/loops of gas• Solar Flares – solar storm, bright bursts of Solar Flares – solar storm, bright bursts of

light on sun’s surfacelight on sun’s surface– Lasts less than 1 hourLasts less than 1 hour

• Solar Winds – continuous stream of high-Solar Winds – continuous stream of high-energy particles released into spaceenergy particles released into space

• Sunspots – dark, cooler areas on sun’s Sunspots – dark, cooler areas on sun’s surfacesurface– Storms in the lower atmosphere of sunStorms in the lower atmosphere of sun

• Sun rotates on an axis like the EarthSun rotates on an axis like the Earth– Gases rotate once every 25 daysGases rotate once every 25 days

• Life cycle of stars from “birth” to Life cycle of stars from “birth” to “death”“death”

• New stars form from gases in a nebulaNew stars form from gases in a nebula– Hydrogen gets clumped together by Hydrogen gets clumped together by

gravitygravity– Begin spinning in a cloud formationBegin spinning in a cloud formation– Collision heat up and nuclear fusion occursCollision heat up and nuclear fusion occurs

• Protostar Protostar – great heat that is given off – great heat that is given off during nuclear fusion causing a new during nuclear fusion causing a new starstar

• Life cycle of star is now fixedLife cycle of star is now fixed• Main factor that shapes the evolution of a star is Main factor that shapes the evolution of a star is

how much how much massmass it began with. it began with.• Stars shine with a red color when most of the Stars shine with a red color when most of the

hydrogen gas has been converted into heliumhydrogen gas has been converted into helium• Star begins to grow and heats up becoming a Star begins to grow and heats up becoming a

giant red stargiant red star• As giant red continues to age the temperature of As giant red continues to age the temperature of

the Helium core rises to abt 200,000,000°Cthe Helium core rises to abt 200,000,000°C– Causing carbon atoms to formCausing carbon atoms to form– Star begins to dieStar begins to die– Gravity causes matter to collapse inward squeezing Gravity causes matter to collapse inward squeezing

tightly becoming tightly becoming White DwarfWhite Dwarf

• Matter extremely denseMatter extremely dense• Not a dead star, shines with hot Not a dead star, shines with hot

white lightwhite light• Stars will slowly dieStars will slowly die• Life span range: Life span range: – 10 billion – 100 billion yrs10 billion – 100 billion yrs

• Mass of massive stars 6x that of sunMass of massive stars 6x that of sun• Take same path as medium-sized stars Take same path as medium-sized stars

except for after red giant stage they do except for after red giant stage they do not become white dwarfsnot become white dwarfs

• Carbon atoms continue to fuse creating Carbon atoms continue to fuse creating heavier elements like oxygen & heavier elements like oxygen & nitrogennitrogen

• Core of massive star so hot that fusion Core of massive star so hot that fusion continues until the heavy element of continues until the heavy element of iron is formediron is formed

• Massive stars begin falling apartMassive stars begin falling apart• Supernova - Supernova - tremendous explosion tremendous explosion

occursoccurs– Lights up sky for weeksLights up sky for weeks– Most famous supernova on record Most famous supernova on record

observed in 1054 by a Chinese observed in 1054 by a Chinese astronomerastronomer• lit the sky for 23 days and seen at night for lit the sky for 23 days and seen at night for

more that 600 days more that 600 days • Crab Nebula – remains of this supernova Crab Nebula – remains of this supernova

• Neutron stars are the result of Neutron stars are the result of supernovassupernovas– Very denseVery dense– Spin rapidly, giving off radio waves as Spin rapidly, giving off radio waves as

pulsespulses– PulsarsPulsars – neutron stars that give off – neutron stars that give off

bursts of radio wavesbursts of radio waves

• Black HoleBlack Hole – swallows matter and – swallows matter and energy as if a cosmic vacuum energy as if a cosmic vacuum cleanercleaner– Result from death of super massive Result from death of super massive

starsstars– No light escapes but sometimes have a No light escapes but sometimes have a

companion starcompanion star• Helps astronomers to find black holesHelps astronomers to find black holes