Chapter 27—Chapter 27—Stars and Stars and GalaxiesGalaxies

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

How Do We Know?How Do We Know?

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

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

Examples of SpectraExamples of Spectra

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

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.

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

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.

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

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)

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

Characteristics of StarsCharacteristics of StarsTemperature: Blue is the hottest

(35000°C)

Red is the coolest(3000°C)

Yellow (our sun)(5500°C)

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

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

Star 1

High luminosity

Far from earth

= lower apparent

magnitude

Star 2

Low luminosity

Close to earth

= higher apparent

magnitude

Apparent Magnitude

v.

Luminosity

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

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

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

B. nonpulsatingEclipsing Binary

2 stars of unequal brightness that revolve around each otherbrightness depends on which one is in front of the other

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

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.

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

Life Stages of StarsLife Stages of Stars

With Solar Masses less than With Solar Masses less than

8 Solar Masses8 Solar Masses

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

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

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

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.

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.

Super NovaSuper Nova

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).

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.

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

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

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

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

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.

The Constellation, OrionThe Constellation, Orion

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