stars and galaxies
DESCRIPTION
Notes on stars and galaxiesTRANSCRIPT
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Chapter 27—Chapter 27—Stars and Stars and GalaxiesGalaxies
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What is a Star?What is a Star?
Star: A body of gas that gives Star: A body of gas that gives off a tremendous amount of off a tremendous amount of radiant energy in the form of radiant energy in the form of
light and heatlight and heat
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How Do We Know?How Do We Know?
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What is Light?What is Light?
A form of A form of electromagnetic radiation which which is energy that travels in wavesis energy that travels in waves
>Electromagnetic radiation is arranged in >Electromagnetic radiation is arranged in a continuum called the a continuum called the electromagnetic electromagnetic spectrumspectrum
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Continuous SpectrumContinuous Spectrum: all visible colors (wavelengths): all visible colors (wavelengths) Emission SpectrumEmission Spectrum: Lines of specific colors : Lines of specific colors
(wavelengths)(wavelengths) Absorption SpectrumAbsorption Spectrum: all visible colors with specific : all visible colors with specific
wavelengths removed forming dark lineswavelengths removed forming dark lines
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Examples of SpectraExamples of Spectra
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Big Bang TheoryBig Bang Theory 15 billion years ago15 billion years ago Universe compressed Universe compressed
into infinitely small into infinitely small space—Primordial space—Primordial AtomAtom
Exploded with sudden Exploded with sudden burst of energyburst of energy
Created small, super Created small, super dense, extremely hot dense, extremely hot universeuniverse
Expanded in all Expanded in all directionsdirections
As things cooled, As things cooled, matter clumped matter clumped forming stars and forming stars and galaxiesgalaxies
100 million years after 100 million years after “big bang” stars “big bang” stars started to formstarted to form
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Evidence supporting Evidence supporting Big Bang Theory…Big Bang Theory…
Remnant of initial Remnant of initial heat--Cosmic heat--Cosmic Microwave Microwave Background Radiation Background Radiation discovered in 1965 discovered in 1965 that fills the entire that fills the entire universeuniverse
Abundance of Abundance of Hydrogen and HeliumHydrogen and Helium
The size of galaxies The size of galaxies relative to their relative to their positions.positions.
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And Evidence And Evidence from the from the
Doppler EffectDoppler Effect
Edwin Hubble (Hubble’s Law) showed that there is Redshift of star Edwin Hubble (Hubble’s Law) showed that there is Redshift of star spectrums which shows that galaxies are moving away from usspectrums which shows that galaxies are moving away from us
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Light and the Universe Light and the Universe
Light YearLight Year—used as a measurement of —used as a measurement of the great distances in space the great distances in space
A A light yearlight year is the distance that a ray of is the distance that a ray of light can travel in a year, or: light can travel in a year, or:
A light year is A light year is 5,865,696,000,000 miles5,865,696,000,000 miles (9,460,800,000,000 kilometers). (9,460,800,000,000 kilometers).
A star or a star system’s distance from A star or a star system’s distance from earth is measured in light years. earth is measured in light years.
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ParallaxParallax A change in an object’s direction A change in an object’s direction
due to a change in the observer’s due to a change in the observer’s position.position.
Astronomers also use parallax to Astronomers also use parallax to calculate the distance to the stars.calculate the distance to the stars.
ParsecParsec—short for “parallax —short for “parallax second”—is a special unit of second”—is a special unit of distance for a star’s distance from distance for a star’s distance from earth. earth.
> 1 parsec = 3.258 light years> 1 parsec = 3.258 light years
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Why Do Stars Twinkle??Why Do Stars Twinkle??
The scientific name for the twinkling of stars is stellar scintillation (or astronomical scintillation)
Stars (except for the Sun) appear as tiny dots in the sky
As their light travels through the many layers of the Earth's atmosphere, the light of the star is bent (refracted) many times and in random directions
This random refraction results in the star winking out (it looks as though the star moves a bit, and our eye interprets this as twinkling)
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Characteristics of StarsCharacteristics of StarsSize: anywhere from 20km to 1 trillion
km in diameter
Mass: the amount of matter
Color: stars can be red, blue, white, orange or yellow
Composition: contain different elementsdetermined using spectra
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Characteristics of StarsCharacteristics of StarsTemperature: Blue is the hottest
(35000°C)
Red is the coolest(3000°C)
Yellow (our sun)(5500°C)
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LuminosityLuminosity—the actual brightness of a star—the actual brightness of a star• Depends on size and temperatureDepends on size and temperature
Apparent MagnitudeApparent Magnitude—A measure of how bright a star appears to be on earth
• the lower the number, higher the brightness• Does not measure how bright a star actually is
Absolute MagnitudeAbsolute Magnitude—A measure of how bright a star would be if all Stars were at the same distance—ten parsecs—from Earth
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0-10-20-30 10 20 30
MagnitudesMagnitudes
DimmerDimmerBrighterBrighter
Our Our SunSun
Sirius Sirius
Brightest in Brightest in the sky from the sky from
EarthEarth
Polaris/North Polaris/North StarStar
-26.5 -2 3 6
We can not see We can not see dimmer than +6 dimmer than +6 with naked eyewith naked eye
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Star 1
High luminosity
Far from earth
= lower apparent
magnitude
Star 2
Low luminosity
Close to earth
= higher apparent
magnitude
Apparent Magnitude
v.
Luminosity
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Hertzsprung-Russel DiagramHertzsprung-Russel Diagram
Relationship between the absolute magnitude Relationship between the absolute magnitude (luminosity) and the temperature of stars.(luminosity) and the temperature of stars.
Spectral Class—designates the color of stars >depends on temperature >Hottest to the coolest >Blue to White to yellow to orange to Red
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Kinds of Starssuper giants- largest of all stars, very luminous
red giants- cooler, large, very luminous
dwarf stars- less luminous, red, orange or yellow
white dwarf- very faint, small and dense
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Variable Stars- vary in brightness over regular periods or cycles
2 types:A. pulsatingchange in brightness as they contract (brighter)
Orexpand (dimmer)
Example: cepheid- yellow supergiant
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B. nonpulsatingEclipsing Binary
2 stars of unequal brightness that revolve around each otherbrightness depends on which one is in front of the other
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Pulsarsstar that releases light and radio waves in pulsesmay be the neutron star formed in a supernovait looks like it pulses because it is rotating, like a searchlight
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A star begins it’s life in a cloud of cold gas and tiny-grained dust called a NEBULA.
Parts of the Nebula begin to condense due to some outside force—a shockwave—which acts upon it.
Due to gravity, the gas and dust pockets continue to condense and their temperature increases.
Eventually, parts of the Nebula begins to glow—PROTOSTARS are formed.
Gravitational contraction of the Protostars continues causing them to become hotter and brighter.
Finally, fusion takes place in the center of a protostar, halting gravitational condensation, and a star is born.
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Stellar MassesStellar Masses
Expressed as multiples of the mass of the sun—Expressed as multiples of the mass of the sun—ONE SOLAR MASSONE SOLAR MASS
1 solar mass is approximately 2 X 101 solar mass is approximately 2 X 1030 30 or or approximately 330,000 Earth massesapproximately 330,000 Earth masses
Solar Mass determines life stages of a starSolar Mass determines life stages of a star
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Life Stages of StarsLife Stages of Stars
With Solar Masses less than With Solar Masses less than
8 Solar Masses8 Solar Masses
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Main Sequence Star (Our Sun)— >90% of all stars >The star is stable >Burns Hydrogen gas to Helium in its core through nuclear fusion > The energy released causes the star to shine. >Stars spend about 90% of their active lifetime as main sequence stars.
Red Giant— >The star begins to run out of fuel and the core begins to shrink >Helium turns into Carbon >Rapid burning of helium causes outer layer to puff out, cooling the star >The star turns red
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Planetary Nebula— >Outer layers are ejected as core continues to shrink >Shell of hot gas >Core is exposed
White Dwarf— >Low mass core continues to shrink creating a white dwarf >Surrounded by the Planetary Nebula
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Stars EvolutionStars EvolutionGreater than 8 Solar MassesGreater than 8 Solar Masses
Hydrogen fuses more quickly and Hydrogen fuses more quickly and when a star starts to die, iron nuclei when a star starts to die, iron nuclei are formedare formed
Star swells to 100 times diameter of Star swells to 100 times diameter of the the sun—Super Giant
Iron nuclei absorbs energy and core Iron nuclei absorbs energy and core quickly and suddenly collapsesquickly and suddenly collapses
Explodes into a brilliant burst of Explodes into a brilliant burst of light—Super Nova
Leaves behind coreLeaves behind core >>neutron star—(<15 solar masses) —(<15 solar masses)
dense mass of neutronsdense mass of neutrons **When 1**When 1stst formed, will spin into a formed, will spin into a
pulsar (pulsations of radiations in regular intervals)
> > Black Hole—(>15 solar masses)—(>15 solar masses) a concentration of mass greata concentration of mass great
enough that the force of gravityenough that the force of gravity will not allow anything to escapewill not allow anything to escape
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Star SystemsStar Systems
• Closest star system to us is Closest star system to us is Alpha Centauri Alpha Centauri which is 4.3 light years away.which is 4.3 light years away.
• The actual star is Proximi Centauri (Alpha The actual star is Proximi Centauri (Alpha Centauri C--4.2 light years away), a red dwarf Centauri C--4.2 light years away), a red dwarf that cannot be seen with the naked eyethat cannot be seen with the naked eye
• This is a multiple star system. Most are This is a multiple star system. Most are binary.binary.
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Novas & SupernovasNovas & Supernovas
Believed to only happen in binary-stars Believed to only happen in binary-stars systems.systems.
Gases from one star hit the surface of Gases from one star hit the surface of another and cause a nuclear type another and cause a nuclear type explosion.explosion.
Supernova is a brilliant burst of light that Supernova is a brilliant burst of light that follows the collapse of the iron core of a follows the collapse of the iron core of a massive star.massive star.
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Super NovaSuper Nova
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Star ClustersStar Clusters
There are larger groups There are larger groups of stars, called of stars, called clustersclusters. . These are relatively These are relatively unorganized collections unorganized collections of stars. (Galaxy) of stars. (Galaxy)
Open ClustersOpen Clusters
Not organized- 100’s of Not organized- 100’s of starsstars
Globular Clusters Globular Clusters
Spherical, round- Spherical, round- 100,000’s of stars100,000’s of stars
We live in a star cluster-We live in a star cluster-the Milky way it is a the Milky way it is a Spiral GalaxySpiral Galaxy
Spiral galaxies are Spiral galaxies are galaxies with a central, galaxies with a central, dense area and spiraling dense area and spiraling arms (which are often arms (which are often sites of star formation). sites of star formation).
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Other GalaxiesOther Galaxies There are several types of There are several types of galaxiesgalaxies the three main ones the three main ones
are: are: SpiralsSpirals are easily identified by their main components. are easily identified by their main components.
They are in the shape of a flat disk with a bright central They are in the shape of a flat disk with a bright central nucleus and spiral arms that extend out from the nucleus and spiral arms that extend out from the nucleus. nucleus.
EllipticalsEllipticals are different from spirals in that they have are different from spirals in that they have very little (or no) gas and dust. They have only stars very little (or no) gas and dust. They have only stars which are concentrated near their centers which are concentrated near their centers
Irregular galaxiesIrregular galaxies have a chaotic appearance, with have a chaotic appearance, with large clouds of gas and dust mixed with both old and large clouds of gas and dust mixed with both old and young stars at random. They have no apparent spiral young stars at random. They have no apparent spiral arms or nuclear bulge. Irregulars are generally faint. arms or nuclear bulge. Irregulars are generally faint. They make up probably about 25% of all galaxies. They make up probably about 25% of all galaxies.
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NebulaeNebulae
Seen only in infraredSeen only in infraredHuge clouds of dust (1%) & gas (99%)Huge clouds of dust (1%) & gas (99%)This is where most stars are born.This is where most stars are born.
Stellar nursery is a nebula ( a large cloud of hydrogen gas in space) in which star formation is occurring
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GalaxiesGalaxies
Major features if the universeMajor features if the universe -100 billion galaxies-each with-100 billions -100 billion galaxies-each with-100 billions
stars.stars.3 types of galaxies3 types of galaxies
1. Spiral1. Spiral
2. Elliptical2. Elliptical
3. Irregular3. Irregular
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3 Types of Galaxies
1.spiral- nucleus with arms extending out
most galaxies are this type
Milky Way is spiral
2. elliptical- oval/ disk shaped
3. irregular- smaller, fainter less common
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ConstellationsConstellations Polaris (North Star)Polaris (North Star) Found at the end of the handle Found at the end of the handle
of the Little Dipper (asterism)-of the Little Dipper (asterism)-which makes up the which makes up the constellation Ursa Minor (Little constellation Ursa Minor (Little Bear)Bear)
Also can be found for using the Also can be found for using the pointer stars in the Big Dipper pointer stars in the Big Dipper (asterism)-which makes up the (asterism)-which makes up the constellation Ursa Major (Big constellation Ursa Major (Big Bear)Bear)
Also used for navigatiional Also used for navigatiional purposespurposes
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QuasarsQuasars
QuasarsQuasars: give off radio & X-waves. They are the : give off radio & X-waves. They are the most distant objects in space. Give off most distant objects in space. Give off tremendous amounts of energy.tremendous amounts of energy.
Quasars give off enormous amounts of energy - Quasars give off enormous amounts of energy - they can be a trillion times brighter than the Sun! they can be a trillion times brighter than the Sun! Quasars are believed to produce their energy Quasars are believed to produce their energy from massive black holes in the center of the from massive black holes in the center of the galaxies in which the quasars are located. galaxies in which the quasars are located. Because quasars are so bright, they drown out Because quasars are so bright, they drown out the light from all the other stars in the same the light from all the other stars in the same galaxy. galaxy.
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The Constellation, OrionThe Constellation, Orion
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There are 88 There are 88 constellations or sky constellations or sky divisionsdivisions
The constellations The constellations change position with change position with each seasoneach season
Some constellations Some constellations only come up during only come up during certain seasons, some certain seasons, some not at allnot at all
Some never change Some never change position due to their position due to their position to the poles—position to the poles—circumpolarcircumpolar
Constellation of Orion is seen during winter