Stars, Galaxies, and the Universe Chapter 2

Stars Section 1 Vocabulary Spectrum Apparent Magnitude Absolute Magnitude Light-Year Parallax

Color of Stars Red and Yellow Blue Blue flame hotter than yellow flame Cool Blue Warm Blue flame hotter than yellow flame Stars different color Betelgeuse-Red Rigel-Blue

Composition of Slides Different elements of gases Inner Layers Very dense and hot Outer 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 Light The 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 spectrum Composition and Temperature Neon sign

Making and ID Neon Sign Emission 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 Work Stars produce spectrums Dark emission lines A 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 Lines The 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 Stars 1800’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 Temperature How hot Temperature differences between stars result in color differences that you can see O stars Blue Hottest Highest temperature to lowest temperature

Differences in Brightness Early astronomers created a system to classify stars based on their brightness. First-magnitude –brightest stars Sixth-magnitude – dimmest stars Some stars are too dim to see Added to the old system Positive numbers- dimmer stars

Apparent Magnitude The 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 Magnitude The 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 Stars Daytime and Nighttime caused by rotation Each season-faces different parts of the sky Different set of constellations

The Apparent Motion of Stars Sun appears to move across the sky Look long enough, the star appear to move Polaris Appear to make one complete circle around Polaris

The Actual Motion of Stars Moving in space Distance makes it hard to see Star pattern slowly change their shape

The Life Cycle of Stars Section 2 Vocabulary Red Giant White Dwarf H-R Diagram Main Sequence Supernova Neutron Star Pulsar Black Hole

The beginning and End of Stars First Stage- ball of gas and dust Gravity pulls it together into a sphere More Dense- Hotter Nuclear Fusion- Hydrogen changes to Helium Older-lose some materials Materials returns to space Forms new stars

Different Types of Stars Stars can be classified: Mass Brightness Color Temperature Spectrum Age Types of stars: Main-sequence Giants Supergiants White Dwarf Classifications can change.

Main-Sequence Stars Second and Longest Stage Energy is generated in the core of the star as hydrogen atoms fuse into helium atoms Releases an enormous amount of energy

Giants and Supergiants Third stage of life a large, reddish star late in its life cycle Loss 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 Dwarfs Final Stages- Same mass as the sun or smaller A 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 Stars 1911-Hertzsprung compared the brightness and the temperature of stars on a graph 1913-Russell made some similar graphs Different data- same results Hertzsprung –Russell Diagram H-R Diagram Tool for studying the lives of stars

Reading the H-R Diagram Temperature is on the bottom Absolute Magnitude is on the left side Blue stars on the left Red stars on the right Bright stars on the top Dim stars on the bottom Main sequence Most of the lifetime

When Stars Get Old Do 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

Supernovas Blue stars May Explode use their hydrogen much faster than stars like the sun generate more energy that stars like the sun Do not have long lives May Explode Supernova Brighter than an entire galaxy for several days

Neutron Stars and Pulsars 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 Holes The 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

Galaxies Section 3 Vocabulary Galaxy Nebula Globular Cluster Open Cluster Quasar

Types of Galaxies Many Different Types 1920’s-classify galaxies By shape Edwin Hubble Still use the galaxy classification

Spiral Galaxies Bulge at the center Spiral Arms Gas, Dust, and New Stars Denser Regions of Gas and Dust

The Milky Way Hard 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 Galaxies One-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 galaxies Dwarf elliptical galaxies

Irregular Galaxies Group of leftovers- “irregulars” Do not fit into any other class Shape-irregular Large Magellanic Cloud close companions of large spiral galaxies

Contents of Galaxies Composed of billions of stars and some planetary systems Form large features Gas clouds Star clusters

Gas Clouds Nebula Large clouds of dust and gas Some Glow others absorb light and hide stars Others reflect starlight and produce some amazing images Some are regions that form new stars Spiral-nebulas Elliptical-very few

Star Clusters Globular 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 Galaxies Observing objects far away Takes 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 Universe Section 4 Vocabulary Cosmology Big Bang Theory

Raisin-Bread Model Imagine a loaf of bread before its baked Each raisin is a certain distance apart As 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 galaxies Galaxies move apart

The Big Bang Theory What 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 Explosion Big Bang Theory 13.7 billion years ago- all the contents of the universe was compressed under extreme pressure, temperature, and density in a very tiny spot Rapidly expanded Matter 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 oven Big 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 Universe Universe 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 Repetition Part of a larger system Cluster 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 collapsing Not enough matter Will continue to expand forever cold and dark