Stars, Galaxies, and the UniverseChapter 2

StarsSection 1 Vocabulary

◦Spectrum◦Apparent Magnitude◦Absolute Magnitude◦Light-Year◦Parallax

Color of StarsRed and Yellow

◦ CoolBlue

◦ WarmBlue flame hotter

than yellow flame

Stars different color

Betelgeuse-RedRigel-Blue

Composition of SlidesDifferent elements of

gasesInner Layers

◦ Very dense and hotOuter Layers

(Atmosphere)◦ Cool Gases

Elements in a star’s atmosphere absorb some of the light that radiates from the star.

Different wavelengths- different elements

The Colors of LightThe band of color

produced when white light passes through a spectrum

Millions of colors-rainbow

Continuous spectrum-shows all color◦ Glowing wire

Spectrograph◦ Break star’s light into a

spectrumComposition and

Temperature◦ Neon sign

Making and IDNeon SignEmission lines-lines

that are made when certain wavelengths of light, or colors, are given off by hot gases.

When an element emits light, only some colors in the spectrum show up, while other colors are missing.

Unique set of bright emission lines◦ Fingerprints

Trapping the Light-Cosmic Detective WorkStars produce

spectrumsDark emission

linesA star’s

atmosphere absorbs certain colors of light in the spectrum, which causes black lines to appear.

Identifying Elements Using Dark Lines

Absorption Spectrum- produced when light from a hot solid or dense gas passes through a cooler gas

A star gives off an absorption spectrum because a star’s atmosphere is cooler than the inner layers of the star.

The black lines represent places where less light gets through.

Identifying Elements Using Dark LinesThe pattern of

lines in a star’s absorption spectrum shows some of the elements that are in the star’s atmosphere.

One element-Easy

More than one element- hard

Classifying Stars1800’s-

astronomers started to collect and classify the spectra of many stars.

Classified according to the elements

Classified in the wrong order

Differences in in TemperatureHow hotTemperature

differences between stars result in color differences that you can see

O stars◦ Blue◦ Hottest

Highest temperature to lowest temperature

Differences in BrightnessEarly astronomers

created a system to classify stars based on their brightness.◦ First-magnitude –

brightest stars◦ Sixth-magnitude –

dimmest starsSome stars are too

dim to seeAdded to the old

systemPositive numbers-

dimmer stars

Apparent MagnitudeThe brightness of a

star as seen from Earth

Depends on the square of the ratio between the light and the light meter

Some stars are brighter than other stars because of their size or energy output, not because of their distance from Earth.

Absolute MagnitudeThe brightness a star

would have at a distance of 32.6 light years away

If all stars were the same distance away, their absolute magnitudes would be the same as their apparent magnitudes.

Sun- ◦ Absolute Magnitude

+4.8 Ordinary

◦ Apparent Magnitude -26.8 Brightest object in the sky

Distance to the Stars Light-Years to measure

distances from Earth to the stars

Stars near the Earth seem to move, while more distant stars seem to stay in one place as earth revolves around the sun.

Parallax-an apparent shift in the position of an object when viewed from different locations◦ Location of the nearer star

seems to shift in relation to the pattern of more distant stars

◦ Only seen through telescopes◦ Parallax and simple

trigonometry to find actual distances

Motions of the StarsDaytime and

Nighttime caused by rotation

Each season-faces different parts of the sky

Different set of constellations

The Apparent Motion of StarsSun appears to

move across the sky

Look long enough, the star appear to move

PolarisAppear to make

one complete circle around Polaris

The Actual Motion of StarsMoving in spaceDistance makes

it hard to seeStar pattern

slowly change their shape

The Life Cycle of StarsSection 2 Vocabulary

◦Red Giant◦White Dwarf◦H-R Diagram◦Main Sequence◦Supernova◦Neutron Star◦Pulsar◦Black Hole

The beginning and End of StarsFirst Stage- ball of gas

and dustGravity pulls it

together into a sphereMore Dense- HotterNuclear Fusion-

Hydrogen changes to Helium

Older-lose some materials

Materials returns to space

Forms new stars

Different Types of StarsStars can be

classified:◦ Mass◦ Brightness◦ Color◦ Temperature◦ Spectrum◦ Age

Types of stars:◦ Main-sequence◦ Giants◦ Supergiants◦ White Dwarf

Classifications can change.

Main-Sequence StarsSecond and

Longest StageEnergy is

generated in the core of the star as hydrogen atoms fuse into helium atoms

Releases an enormous amount of energy

Giants and SupergiantsThird stage of lifea large, reddish star

late in its life cycleLoss of hydrogen

causes center of the star to shrink

Atmosphere of the star grows very large and cools

Red giants- 10 times bigger than the sun

Supergiants- 100 times bigger than the sun

White DwarfsFinal Stages-Same mass as the sun

or smallerA small, hot, dim star

that is the leftover center of an old star

No hydrogen left and can no longer generate energy by fusing hydrogen atoms into helium atoms

Can shine billions of years before cooled

A Tool for Studying Stars1911-Hertzsprung

compared the brightness and the temperature of stars on a graph

1913-Russell made some similar graphs ◦ Different data- same

resultsHertzsprung –Russell

Diagram H-R Diagram

Tool for studying the lives of stars

Reading the H-R DiagramTemperature is on

the bottomAbsolute Magnitude

is on the left sideBlue stars on the left Red stars on the

rightBright stars on the

topDim stars on the

bottomMain sequence

◦ Most of the lifetime

When Stars Get OldDo not stay on the

main sequence forever

Average stars- red giants then white dwarfs

Stars that are larger than the sun- may explode◦ Supernovas◦ Neutron stars◦ Pulsars◦ Black holes

SupernovasBlue stars

◦ use their hydrogen much faster than stars like the sun

◦ generate more energy that stars like the sun

◦ Do not have long livesMay Explode

◦ Supernova◦ Brighter than an

entire galaxy for several days

Neutron Stars and PulsarsNeutron Star

◦ After a supernova Material in the center are

squeezed together to form a new star

About two times the mass of the sun

The particles are forced together to form neutrons

Pulsars ◦ Neutron Star spinning◦ Sends out a beam of

radiation that spins rapidly

◦ Beam is detected on Earth by radio telescopes as rapid clicks or pulses

Black HolesThe leftovers of a

supernova are so massive that they collapse to form a black hole

Do not give off light, finding them is difficult

If a star is nearby, some gas or dust from the star will spiral into the black hole and give off X-rays

GalaxiesSection 3 Vocabulary

◦Galaxy◦Nebula◦Globular Cluster◦Open Cluster◦Quasar

Types of GalaxiesMany Different

Types1920’s-classify

galaxies◦ By shape◦ Edwin Hubble

Still use the galaxy classification

Spiral GalaxiesBulge at the

centerSpiral Arms

◦ Gas, Dust, and New Stars

◦ Denser Regions of Gas and Dust

The Milky WayHard to tell what

type of galaxy◦ Gas, dust, and

stars keep astronomers from having a good view

They think it is a spiral galaxy.

Elliptical GalaxiesOne-third of all galaxies

are massive blobs of stars.

Elliptical Galaxies- bright centers and very little dust and gas

Contain mostly old stars

No to little free flowing gas

Giant elliptical galaxiesDwarf elliptical galaxies

Irregular GalaxiesGroup of

leftovers- “irregulars”

Do not fit into any other class

Shape-irregularLarge Magellanic

Cloud◦ close companions

of large spiral galaxies

Contents of GalaxiesComposed of

billions of stars and some planetary systems

Form large features◦ Gas clouds ◦ Star clusters

Gas CloudsNebulaLarge clouds of dust

and gasSome Glowothers absorb light

and hide starsOthers reflect starlight

and produce some amazing images

Some are regions that form new stars

Spiral-nebulasElliptical-very few

Star ClustersGlobular clusters-

groups of older stars◦ Up to one million stars◦ Located in a spherical

halo that surrounds spiral galaxies

◦ Common near giant elliptical galaxies

Open clusters-closely grouped stars◦ Located along the spiral

disk of a galaxy◦ Newly formed-many

bright blue stars◦ Few hundred to a few

thousand stars

Origin of GalaxiesObserving objects far

awayTakes time for light

to travel through space, looking through a telescope is like looking back in time

Shows what early galaxies looked like

How they change over time and what caused them to form

Formation of the UniverseSection 4 Vocabulary

◦Cosmology◦Big Bang Theory

Raisin-Bread Model Imagine a loaf of bread

before its bakedEach raisin is a certain

distance apartAs the dough rises, it

expands and all of the raisins begin to move apart

Other raisins are moving away from it

The universe is expanding

Raisins as galaxiesGalaxies move apart

The Big Bang TheoryWhat it would

look like in reverse

It look like it is contracting.

All matter would come together at a single point

Squeezed into one small space

A Tremendous ExplosionBig Bang Theory13.7 billion years ago-

all the contents of the universe was compressed under extreme pressure, temperature, and density in a very tiny spot

Rapidly expandedMatter began to come

together and form galaxies

Cosmic Background Radiation

1964- twos scientists using a huge antenna accidentally found radiation coming from all directions in space

Cosmic background radiation

Kitchen ovenBig Bang Theory- the

thermal energy from the original explosion was distributed in every direction as the universe expanded

Now fills all of space

Structure of the UniverseUniverse

stretches out farther than astronomers can see with their advanced instruments

Not simply scattered through the universe in a random pattern

Has structure

A Cosmic RepetitionPart of a larger

systemCluster or group of

galaxies can be made up of smaller star clusters and galaxies

Can include planetary systems

Other planets can be detected in orbit around other stars

common

How Old Is the Universe?One Way scientists

can calculate the age of the universe is to measure the distance from Earth to various galaxies

Estimate the age of the universe and predict its expansion

To calculate the ages of old, nearby stars

A Forever Expanding Universe

As they move farther apart they get older and stop forming stars

The expansion of the universe depends on how much matter the universe contains

Gravity could eventually stop expanding◦ Eventually start

collapsingNot enough matter

◦ Will continue to expand forever

◦ cold and dark