STARS, GALAXIES, CONSTELLATIONS

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STARS, GALAXIES, CONSTELLATIONS

• CHAPTER 28

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WHAT IS LIGHT?

• A FORM OF ELECTROMAGNETIC RADIATION
• ENERGY THAT TRAVELS IN WAVES AT THE SPEED OF
  LIGHT
• 300,000KM/SECOND

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LIGHT

• THE LENGTH OF THE WAVE DETERMINES THE
  CHARACTERISTIC OF THE ELECTROMAGNETIC RADIATION
• WAVE LENGTH DISTANCE FROM ONE CREST TO ANOTHER

CREST
TROUGH
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ELECTROMAGNETIC SPECTRUM

• THE RANGE OF LIGHT WAVES IN THE UNIVERSE
• RADIO WAVES LONGEST WAVES
• GAMMA RAYS SHORTEST WAVES

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LIGHT WAVES

• STARS LIKE OUR SUN EMIT A WIDE RANGE OF
  WAVELENGTHS
• VISIBLE WHITE LIGHT IS A VERY SMALL PART OF THE
  SPECTRUM
• SEE TEXT PAGE 613
• ROY G BIV
• FROM LONG TO SHORT (RED TO VIOLET)

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ELECTROMAGNETIC SPECTRUM
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SPECTRUM

• ASTRONOMERS USE THE SPECTRA TO DETERMINE THE
  COMPOSITION OF STARS
• SPECTROSCOPES ARE INSTRUMENTS THAT BREAK DOWN THE
  LIGHT INTO ITS PARTS

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CONTINUOUS SPECTRUM
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CONTINUOUS SPECTRUM

• UNBROKEN BAND OF COLORS
• SHOWS THAT ITS SOURCE IS EMITTING LIGHT OF ALL
  VISIBLE WAVELENGTHS
• EMITTED BY
• GLOWING SOLIDS, LIKE HOT FILAMENTS
• GLOWING LIQUIDS, LIKE MOLTEN IRON
• HOT COMPRESSED GASES INSIDE STARS

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EMISSION SPECTRUMneon
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EMISSION SPECTRUMHYDROGEN
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EMISSION SPECTRUMHELIUM
THIS IS HOW WE IDENTIFY THE ELEMENTS IN STARS AND
PLANETS.
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ABSORPTION SPECTRUM
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ABSORPTION SPECTRUM

• CONTINUOUS SPECTRUM CROSSED BY DARK LINES
• FORMS WHEN LIGHT FROM A GLOWING OBJECT PASSES
  THROUGH A COOLER GAS WHICH ABSORBS SOME OF THE
  WAVELENGTH
• INDICATES THE COMPOSITION OF THE STARS OUTER
  LAYER
• ALSO USED TO DETERMINE THE COMPOSITION OF A
  PLANETS ATMOSPHERE

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DOPPLER EFFECT

• SPECTRA OF STARS ARE COMPARED TO EMISSION SPECTRA
  OF ELEMENTS
• THE DARK LINES MAY BE SHIFTED TO THE LEFT OR RIGHT

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BLUE SHIFT IF A STAR IS APPROACHING EARTH THE
WAVELENGTH BECOMES SHORTER
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REDSHIFT IF A STAR IS MOVING AWAY FROM EARTH
THE WAVELENGTH BECOMES LONGER
CAN ALSO DETERMINE THE SPEED AT WHICH STARS ARE
MOVING
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STARS AND THEIR CHARACTERISTICS

• CONSTELLATIONS A GROUP OF STARS THAT APPEAR TO
  FORM A PICTURE IN THE SKY
• ANCIENT PEOPLE SAW THE STARS AND GAVE THEM NAMES
  AND STORIES
• EACH CULTURE HAD THEIR OWN STORY GREEK, ROMAN,
  MAYAN, ETC..

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CONSTELLATIONS

• 88 CONSTELLATIONS IN THE SKY
• SOME CAN BE SEEN FROM THE NORTHERN HEMISPHERE AND
  SOME FROM THE SOUTHERN HEMISPHERE
• SOME CAN BE SEEN IN THE WINTER AND SOME IN THE
  SUMMER AND SOME ALL YEAR LONG

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CIRCUMPOLAR CONSTELLATIONS

• REVOLVE AROUND THE NORTH STAR
• URSA MAJOR (BIG DIPPER)
• URSA MINOR (LITTLE DIPPER)
• DRACO
• CEPHEUS
• CASSIOPEIA

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APPARENT MOVEMENT OF STARS

• CAUSED BY THE ROTATION AND REVOLUTION OF OUR
  EARTH
• DISTANCES TO THE STARS ARE MEASURED BY THE LIGHT
  THAT THEY EMIT
• MEASURED IN LIGHT YEARS

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MEASURING THE UNIVERSE

• ASTRONOMICAL UNIT DISTANCE FROM THE SUN TO THE
  EARTH
• 150 MILLION KM OR 93 MILLION MILES
• MEASURING THE DISTANCE TO STARS WOULD NOT BE
  PRACTICAL USING AUs

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MEASURING THE UNIVERSE

• ALPHA PROXIMA OUR NEAREST STAR BESIDES OUR SUN
  IS 40 TRILLION KM AWAY 4.2 LIGHT YEARS AWAY
• USING AUs IS IMPRACTICAL BECAUSE OF THE GREAT
  DISTANCES
• SO WE USE LIGHT YEARS
• THE DISTANCE IT TAKES LIGHT TO TRAVEL IN ONE
  YEAR 9.5 TRILLION KM

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PHYSICAL PROPERTIES OF STARS

• SIZE
• DENSITY
• MASS
• COLOR/TEMPERATURE
• OUR SUN IS AVERAGE IN ALL THESE CATEGORIES

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SIZE

• STAR SIZE VARIES GREATLY FROM SMALLER THAN THE
  EARTH TO LARGER THEN 2,000 TIMES THE DIAMETER OF
  OUR SUN

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DENSITY

• DENSITY RANGES ARE MUCH MORE VARIED
• BETELGEUSE IS ONE/TEN MILLIONTH AS DENSE AS OUR
  SUN
• SIRIUS SO DENSE THAT ONE TEASPOON WOULD WEIGH
  MORE THAN A TON ON EARTH

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MASS

• MASS RANGES LARGER THAN 50 TIMES OUR SUN,
  (WHICH ARE VERY RARE) TO ONE/100TH THE MASS OF
  OUR SUN

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COLOR

• COLOR DEPENDS ON THE SURFACE TEMPERATURE
• BLUE/WHITE YELLOW ORANGE/RED
• 30,0000C 5,5000 C 3,0000C

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ELEMENTS IN STARS

• HYDROGEN..70
• HELIUM..28
• CARBON, OXYGEN, NITROGEN, CALCIUM, SODIUM2
• SPECTRUM ANALYSIS DETERMINES THIS

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STAR BRIGHTNESS

• APPARENT MAGNITUDE HOW BRIGHT THE STAR APPEARS
  TO AN OBSERVER ON THE EARTH
• EACH LEVEL OF MAGNITUDE IS 2.5 TIMES BRIGHTER
  THAN THE LAST
• 1ST MAGNITUDE STAR IS 2.5 TIMES BRIGHTER THAN A
  2ND MAGNITUDE
• FAINTEST STARS THAT CAN BE SEEN ARE 6TH MAGNITUDE
  STARS

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LUMINOSITY

• TELLS US HOW BRIGHT A STAR REALLY IS. DEPENDS ON
  THE SIZE AND TEMPERATURE OF THE STAR
• HOT STARS ARE MORE LUMINOUS THAT COOL STARS
• STARS THAT ARE CLOSER TO THE EARTH APPEAR TO BE
  BRIGHTER EVEN THOUGH THEY MAY BE LESS LUMINOUS

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ABSOLUTE MAGNITUDE

• ASTRONOMERS USE THIS MEASURE
• IT IS THE BRIGHTNESS OF THE STARS AS IF THEY WERE
  ALL PLACED THE SAME DISTANCE FROM THE EARTH
• DISTANCE IS 32.6 LY AWAY
• SUN 4.8 ABSOLUTE MAGNITUDE
• RIGEL -6.4
• THE LOWER THE NUMBER THE GREATER THE ABSOLUTE
  MAGNITUDE

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KINDS OF STARS

• RED GIANTS
• VARIABLE STARS
• CEPHIEDS
• DWARF STARS
• SUPERGIANTS
• ECLIPSING BINARY
• PULSARS

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KINDS OF STARS

• RED GIANTS HUGH RED STARS, VERY LUMINOUS BECAUSE
  THEY ARE SO BIG
• SUPER GIANTS HUNDREDS OF TIMES MORE LUMINOUS
  THAN RED GIANTS
• EX BLUE-WHITE RIGEL
• WHITE YELLOW CANOPUS
• RED ANTARES AND BETELGEUS

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KINDS OF STARS

• DWARF STARS LESS LUMINOUS
• HAVE AN ABSOLUTE MAGNITUDE NO BRIGHTER THAN 1
• MOST ARE RED, YELLOW, OR ORANGE
• GREAT DENSITY BECAUSE OF TIGHT PACKING OF THE
  ATOMIC NUCLEI

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KINDS OF STARS

• VARIABLE STARS VARY IN BRIGHTNESS
• PULSATING STARS CEPHEID VARIABLES HAVE BRIGHT
  DIM PERIODS FROM 1 TO 50 DAYS
• CONTRACTION BRIGHTER HOTTER
• EXPANSION DIMMER - COOLER

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PULSATING STARS

• VERY IMPORTANT TO ASTRONOMERS BECAUSE THEY USE
  THESE TO CALCULATE DISTANCES TO GALAXIES THAT
  CONTAIN THESE STARS

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KINDS OF STARS

• ECLIPSING BINARY REALLY TWO STARS THAT REVOLVE
  AROUND EACH OTHER
• IF THEY ARE OF UNEQUAL BRIGHTNESS THEY LOOK LIKE
  THEY ARE PULSATING
• PULSARS BELIEVED TO BE NEUTRON STARS FORMED IN
  SUPERNOVAS THE FASTEST ONE KNOWN PULSES AT 642
  TIMES PER SECOND

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LIFE CYCLES OF STARS

• BIRTH OF A STAR
• FIRST START OUT AS A NEBULA
• A CLOUD OF GAS AND DUST
• CONSIST OF 99 HYDROGEN GAS AND 1DUST PARTICLES

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LIFE CYCLE OF A STAR

• PROTOSTAR
• CLOUD CONDENSES
• MATERIAL STARTS TO GLOW AND BECOME HOT
• EVENTUALLY THE CENTER BECOMES SO HOT FUSION OCCURS

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LIFE CYCLE OF A STAR

• MAIN SEQUENCE STARS
• BURNS FOR BILLIONS OF YEARS (OUR SUN)
• DWARF STARS
• BURNS FOR MANY BILLIONS OF YEARS
• MASSIVE STARS
• BURNS FOR JUST A FEW BILLION YEARS

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LIFE CYCLE OF STARS

• THE LENGTH OF THE LIFE CYCLE DEPENDS ON THE
  STARTING MATERIAL FOR THE STAR
• MORE MATERIAL, BIGGER STARS, SHORTER LIFE SPAN
• LESS MATERIAL, SMALLER STARS, LONGER LIFE SPAN

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LIFE CYCLE OF STARS

• DEATH OF A STAR
• FOR MAIN SEQUENCE STARS
• STABLE STAR
• RED GIANT
• PLANETARY NEBULA
• WHITE DWARF

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LIFE CYCLE OF STARS

• FOR MASSIVE STARS
• STABLE STAR
• RED SUPERGIANT
• SUPER NOVA
• NEUTRON STAR OR BLACK HOLE

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GALAXIES AND THE UNIVERSE

• OUR UNIVERSE IS ABOUT 14 BILLION YEARS OLD
• STARTED WITH THE BIG BANG
• ALL MATTER EXISTED IN AN INCREDIBLY HOT DENSE
  STATE
• IT THEN EXPANDED AT AN INCREDIBLE SPEED
• SPACE ITSELF WAS EXPANDING

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OUR UNIVERSE

• THE TEMPERATURE OF THE UNIVERSE COOLED TO A POINT
  WHERE ATOMS COULD EXIST
• THERE IS EVIDENCE OF THIS FROM REDSHIFT
• DISCOVERED BY EDWIN HUBBLE
• http//www.pbs.org/wgbh/nova/origins/universe.html
  

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GALAXIES

• SYSTEMS CONTAINING MILLIONS OR EVEN BILLIONS OF
  STARS
• THERE ARE 50-100 BILLION GALAXIES IN THE UNIVERSE
• MOST ARE MILLIONS OF LIGHT YEARS APART
• WE LIVE IN THE MILKY WAY GALAXY WHICH IS A SPIRAL
  GALAXY

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MILKY WAY GALAXY

• SPIRAL GALAXY
• 100,000 LIGHT YEARS IN DIAMETER
• 10,000 LIGHT YEARS THICK

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MILKY WAY GALAXY
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WHERE ARE WE?

• MILKY WAY BELONGS TO A GROUP CALLED THE LOCAL
  GROUP
• THIS CONSISTS OF MORE THAN 30 GALAXIES
• OUR NEIGHBORS
• 2MAGELLANIC CLOUDS SEEN FROM THE SOUTHERN
  HEMISPHERE W/O A TELESCOPE

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WHERE ARE WE?

• ANDROMEDA GALAXY VISIBLE FROM THE NORTHERN
  HEMISPHERE, VERY FAINT
• MILKY WAY AND ANDROMEDA ARE THE MOST MASSIVE
  GALAXIES IN THE LOCAL GROUP

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OUR ADDRESS IN THE UNIVERSE

• THE LOCAL GROUP AND HUNDREDS OF OTHERS SURROUND
  THE VIRGO CLUSTER CONSISTING OF AS MANY AS 2,000
  GALAXIES
• THE LOCAL CLUSTER IS 10,000 GALAXIES IN OUR AREA
  OF THE UNIVERSE

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TYPES OF GALAXIES
ELLIPTICAL GALAXY
SPIRAL GALAXIES
IRREGULAR GALAXY
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GALAXIES

• NORMAL GALAXIES EMIT LIGHT THAT IS THE TOTAL OF
  ITS STARS
• ACTIVE GALAXIES EMIT MORE LIGHT THAN COULD BE
  GIVEN OFF BY ALL OF THE STARS
• THESE MAY BE POWERED BY A BLACK HOLE IN THE
  CENTER OF THE GALAXY

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GALAXIES

• QUASARS
• EXTREMELY DISTANT OBJECTS 12 BILLION LIGHT YEARS
  AWAY
• EXTREMELY LUMINOUS
• BLAZARS ACTIVE GALAXY WITH ITS JETS POINTED
  TOWARD THE EARTH