Stars

Chapter 21

The Branches of Earth Science

• Astronomy: The study of the planets, stars, and other objects in space.

The Branches of Earth Science

• Lithosphere: the land masses of earth

• Litho means rock

The Branches of Earth Science

• Hydrosphere: waters of the earth

– Hydro means water

The Branches of Earth Science

Atmosphere: The envelope of gases that surround the Earth as well as space and stars.

Tools Used to Study Stars

• Spectroscope: Breaks light from a distant star into its characteristic color

• SPECTRUM: the band of colors that forms as light passes through a prism

• Used to see if galaxies are moving away or toward the earth

Tools Used to Study Stars

Telescopes: device that makes distant objects appear closer

• Types of Telescopes– Optical

– Radio

– X-Ray

– U-V

– Infrared

Constellations

Constellations: group of stars that formed patterns

How do They Get Their Name?

• Different cultures gave differentnames to the constellations

For Example: The Greeks named constellations according to myths

•

The same constellation can have different names in different culturesGreek OrionSumerian SheepChina Three

Why are Constellations

Important?

• Navigation

– Sailors use Polaris (North Star)

– Important in space navigation

• Used to predict the weather.

Best Known Constellations

• Big Bear or UrsaMajor

• Very similar to Big Dipper

– Has pointer stars to Polaris

• Little Bear or UrsaMinor

• Very similar to Little Dipper

What are Stars Like?

• Stars are made up of mostly hydrogen

• Stars produce energy through nuclearfusion.

Characteristics of Stars

• There are 4 major characteristics of starts that scientists use to classify stars

• Color & Temperature

• Size

• Composition

• Brightness

Color & Temperature

• A stars colorreveals its surfacetemperature

–The surface temperature is lower than the core temperature due to nuclear fusion.

• Stars are very Patriotic when it comes to color

Coldest Red

White

Hottest Blue

5 Categories of Sizes

Neutron (16-20 km diameter)

White dwarf (size of Earth)

Medium Size (the sun) *MOST

STARS*

Giant (10-1000 x’s the sun)

Super Giant (1000 x the diameter of the

sun)

Smallest

Largest

The Sizes of Super Giant Stars

Look at the size of the sun compared to the stars, it is almost invisible

Composition

(Chemical Makeup)

• Most stars have the same general composition

– 73% Hydrogen (Most Common)

– 25% Helium (2nd most common)

– 2% Other Elements

Composition Continued

• Scientists use a spectroscope to identify characteristics

–Characteristic: Something that identifies an object

–Elements have “Fingerprint” color characteristics

•They have a unique set of lines in the spectrum

Brightness

(Also called Magnitude)

Depends on…

• Temperature

• Size

• Distance

• Apparent Brightness: the brightness of a star as it appears on Earth.

• Absolute Magnitude: The amount of light the star actually givesoff

Measuring Distance to Stars

• Light Year- Astronomers use light years to measure the distances between stars

–A light year is the distance that light travels in one year

•9,460,730,472,580.8 km

•5,878,630,000,000 miles

Parallax

• Parallax- the apparent change in the position of a star in the sky.

–The change is due to the changein the Earth’ position as the

Earth revolves around

the sun.

Parallax

Hertzsprung-Russell Diagram:

(H-R Diagram)

• It is a scatter plot

• Shows the relationship between absolute brightness and surface temperature

• This is the single most important diagram that astronomers use

• Uses of H-R Diagram

–Classify Stars

–Understand how stars change over time

H-R Diagram

Brightest

Absolute

Magnitude

Dimmest

Hottest Coolest

Surface Temp

H-R Diagram

H-R Diagram

• Main sequence: the area where the most stars are located

• Extends from the upper left corner to the lower right corner

• 90% of stars are located here

Life Cycle of a Star

• All stars start with a NEBULA

–Nebula is a large cloud of gas and dust that forms protostar with gravity

• Then Nuclear Fusion occurs (atoms combine to form heavier atoms)

• The star takes 2 different paths depending on their size

Life Cycle of Stars

Lower Mass Stars

• Giant Star: outer layer expands

–White Dwarf: extremely dense

–Black Dwarf: dead

Life Cycle of Stars

• Higher Mass Stars

–Super Giant: Fusion continues until iron is formed

–Explosion Occurs: No more nuclearfusion

•Super Nova: Star breaks apart

–Neutron Star

–Black Hole

Death of Star

• When a star begins to run out of fuel, its core shrinks and its outer portion expands

–White Dwarf

–Neutron Star

–Black Hole

Multiple Star Systems

• Multi Star System: Star system with one or more companion stars

–Most stars have companions but not all stars

•The sun does not have a companion

Multiple Star System

• Example of multi star system: ALPHA CENTURI: a three star system that is the CLOSEST star to the sun.

– Proxima Centuri

– Alpha century A

– Alpha Century B

Multiple Star Systems

• Binary Stars: Star systems with 2 stars

• Bi = 2 (remember bicycle)

• Eclipsing Binary Star System

–The larger companion blocks the smaller companion

Star Clusters

Star Clusters:Large Groupings of Stars

Open Cluster

• Loose and disorganized appearance

• Contain 100- 1000 stars

• young stars

Star Clusters

Globular Cluster

• more common round, densely packed stars

• 100,000 to 1,000,000

• older stars

Galaxies

• Galaxy is a huge collection of stars bound by gravity

–Contain various star groups

• Billions of galaxies in the universe

• 3 Types of Galaxies

Spiral Galaxy

Elliptical Galaxy

Irregular Galaxy

The Milky Way

• The galaxy we live in

• Spiral shaped

• Looks like a milky or whitish band in the sky

•Sun is located in one of the spiral arms

Milky Way Galaxy•It has 400 billionstars

•It takes the sun and planets over 200 million years to move around the center of the milky way

Big Bang Theory

• Theory is an idea that is supported by evidence

• The universe began to expand with the explosion of concentrated matter and energy and has been expanding ever since