earth science notes

Earth Science NotesEarth Science NotesStars and GalaxiesStars and Galaxies

What is a Star?What is a Star?

A A starstar is a massive, luminous ball of is a massive, luminous ball of plasma that is held together by gravity.plasma that is held together by gravity.

StarsStars shines due to nuclear fusion in its shines due to nuclear fusion in its core releasing energy that radiates into core releasing energy that radiates into space.space.

When stars form they are composed of When stars form they are composed of about 70% hydrogen and 28% helium by about 70% hydrogen and 28% helium by massmassThere is a small fraction of heavier elements. There is a small fraction of heavier elements.

Classifying StarsClassifying Stars

Stars are classified by their Stars are classified by their luminosityluminosity (brightness) and the temperature. (brightness) and the temperature. Hetzsprung and Russell developed a graph Hetzsprung and Russell developed a graph

that shows the relationship between that shows the relationship between luminosity and temperature.luminosity and temperature.

Three main classificationThree main classificationMain sequence Main sequence DwarfsDwarfsGiantsGiants

Classifying StarsClassifying StarsThe Hertzsprung-Russell DiagramThe Hertzsprung-Russell Diagram


The The Hertzsprung-Hertzsprung-Russell Russell DiagramDiagram


Main Sequence StarsMain Sequence StarsRun diagonally across H-R diagramRun diagonally across H-R diagramBrightness increases as temperature Brightness increases as temperature

increasesincreasesThe sun is near the middle of the sequenceThe sun is near the middle of the sequence

Around 90% of all stars are main Around 90% of all stars are main sequencesequence


Dwarf StarsDwarf StarsWhite dwarfs – White dwarfs – hot but small (bottom-left hot but small (bottom-left

of H-R diagram)of H-R diagram)Red Dwarfs – Red Dwarfs – cool but small (bottom-right cool but small (bottom-right

of H-R diagram)of H-R diagram)


Giant StarsGiant Stars Star with substantially Star with substantially

larger radius and larger radius and luminosity than a main luminosity than a main sequence star of the same sequence star of the same surface temperaturesurface temperature

Some Giants are large but Some Giants are large but not hotnot hot

Super-Giants are even Super-Giants are even largerlarger

Evolution of StarsEvolution of Stars

All stars begin as begin as nebulasAll stars begin as begin as nebulas NebulasNebulas – large clouds of gas – large clouds of gas

and dust and dust As particles in the nebula As particles in the nebula

contract they increase in contract they increase in temperature until the reach 10 temperature until the reach 10 million K. This is when fusion million K. This is when fusion begins. begins.

Energy given off from the fusion Energy given off from the fusion process powers the starprocess powers the star


Two series for starsTwo series for starsNebula Nebula high mass star high mass star main main

sequence sequence red supergiant red supergiant supernova supernova black hole or neutron star black hole or neutron star

Nebula Nebula low mass star low mass star main main sequence sequence red giant red giant white dwarf white dwarf


Main Sequence to Giant StarsMain Sequence to Giant StarsWhen hydrogen in a star is depleted, the When hydrogen in a star is depleted, the

fusion process begins to stop. fusion process begins to stop. The core collapses and heats up.The core collapses and heats up.The outer layers of the star begin to cool The outer layers of the star begin to cool

and expand. This stage of the life cycle is and expand. This stage of the life cycle is called a called a giantgiant..


White DwarfsWhite DwarfsWhen a stars core uses up its fuel it When a stars core uses up its fuel it

contracts even more and its outer layers contracts even more and its outer layers escape to space.escape to space.This leave behind a hot, dense coreThis leave behind a hot, dense coreAt this stage the stars becomes a At this stage the stars becomes a white white

dwarfdwarfWhite dwarfs are about the size of the White dwarfs are about the size of the

Earth. They are dim and hot stars.Earth. They are dim and hot stars.

Evolution of StarsEvolution of StarsSupergiantsSupergiants In massive stars, the core heats up to In massive stars, the core heats up to

extremely high temperatures and heavier extremely high temperatures and heavier elements form via fusion, the star expands elements form via fusion, the star expands into a into a supergiantsupergiant..


SupernovasSupernovasOnce an iron core forms the star collapses and a Once an iron core forms the star collapses and a

shockwave travels through the star. The outer shockwave travels through the star. The outer portion of the star explodes and creates a portion of the star explodes and creates a supernovasupernova..

Evolution of StarsEvolution of StarsNeutron Stars Neutron Stars Sometimes when the core of a Sometimes when the core of a

supernova collapses it will supernova collapses it will shrink from 3 times the size of shrink from 3 times the size of the sun to about 20 km. Only the sun to about 20 km. Only neutrons can exist at this neutrons can exist at this density.density.

One teaspoon of a neutron One teaspoon of a neutron star is about 600 million star is about 600 million metric tonsmetric tons

Evolution of StarsEvolution of StarsBlack HolesBlack HolesSometimes a supernova’s core can Sometimes a supernova’s core can

collapse to a point. The gravity at this collapse to a point. The gravity at this point is so great that is pulls everything in, point is so great that is pulls everything in, even light. even light.

Evolution of StarsEvolution of StarsBlack HolesBlack Holes

ConstellationsConstellations

Constellations are patterns made of stars Constellations are patterns made of stars in the skyin the sky

Stars appear close together in the sky, Stars appear close together in the sky, however, they are actually light years from however, they are actually light years from each othereach other


Some constellations are visible only in the Some constellations are visible only in the northern or the southern hemispherenorthern or the southern hemisphereCircumpolar constellations appear to rotate Circumpolar constellations appear to rotate

around Polaris (north star)around Polaris (north star) Some constellations are only visible during Some constellations are only visible during

certain times of the yearcertain times of the year

Circumpolar ConstellationsCircumpolar Constellations

ConstellationsConstellationsSome stars in constellations appear brighter Some stars in constellations appear brighter

than others.than others. This can be due to two things:This can be due to two things: The stars actual luminosity (brightness)The stars actual luminosity (brightness)

Actual magnitudeActual magnitude – how much light is given off by – how much light is given off by starstar

The stars distance The stars distance Apparent magnitudeApparent magnitude – how much light is received on – how much light is received on

Earth Earth Stars far away Stars far away appear dimmerappear dimmer

Measurements in SpaceMeasurements in Space

ParallaxParallax – the apparent change in position – the apparent change in position of object when viewed from different of object when viewed from different perspectivesperspectives


Light yearLight year – measurement of distance – measurement of distanceThe distance light travels in 1 yearThe distance light travels in 1 year

9.5 trillion km / year9.5 trillion km / year

Astronomical UnitAstronomical Unit – distance from Earth – distance from Earth to Sun = 1 AUto Sun = 1 AU

Solar MassSolar Mass – the mass – the mass

of our sun = 1 solar massof our sun = 1 solar mass


Wavelengths of light can be measured to Wavelengths of light can be measured to determine the composition of starsdetermine the composition of starsSpectra of elements are like fingerprints, they Spectra of elements are like fingerprints, they

will tell you what elements are presentwill tell you what elements are present

Galaxies and The Universe Galaxies and The Universe

Galaxy Galaxy – large group of stars, gas, and dust – large group of stars, gas, and dust held together by gravityheld together by gravity

Galaxies are separated Galaxies are separated

by great distances by great distances

millions of lightmillions of light

yearsyears

Galaxies and The UniverseGalaxies and The Universe

Our galaxy is the Milky WayOur galaxy is the Milky WayWe are located on one of the spiral armsWe are located on one of the spiral armsThere is a black hole located at the centerThere is a black hole located at the center

The Milky WayThe Milky Way


Three types of GalaxiesThree types of GalaxiesSpiral – have spiral arms that swing out Spiral – have spiral arms that swing out

from the center (Like Milky Way)from the center (Like Milky Way)

Galaxies and The UniverseGalaxies and The Universe Elliptical – football shapedElliptical – football shaped


Irregular – have many different shapesIrregular – have many different shapes

Origin of the UniverseOrigin of the Universe

Three Models the Universes OriginThree Models the Universes Origin The Steady-State TheoryThe Steady-State Theory

Suggest universe is the same as it has always beenSuggest universe is the same as it has always been

The Oscillating ModelThe Oscillating Model Suggest that the universe expands and contracts over Suggest that the universe expands and contracts over

timetime

The Big Bang TheoryThe Big Bang Theory Suggest universe began as an explosion and has Suggest universe began as an explosion and has

expanded ever sinceexpanded ever since

Origin of the UniverseOrigin of the Universe

The Big Bang TheoryThe Big Bang TheoryEvidence suggest that the Evidence suggest that the

universe is expanding. universe is expanding. Scientist have theorized Scientist have theorized that it has expanded from that it has expanded from one pointone point

According to this theory the According to this theory the universe began with an universe began with an enormous explosionenormous explosion

Expansion of the UniverseExpansion of the Universe

As the universe expands, some stars are moving As the universe expands, some stars are moving toward us and some move away. This causes toward us and some move away. This causes an apparent change in the light we seean apparent change in the light we see Red shiftRed shift – light moving toward Earth appears more – light moving toward Earth appears more

red (toward the red end of the spectrum)red (toward the red end of the spectrum) Blue shiftBlue shift - light moving away from Earth appears - light moving away from Earth appears

more blue (toward the blue end of the spectrum) more blue (toward the blue end of the spectrum)

Expansion of the UniverseExpansion of the Universe

Redshift and Redshift and BlueshiftBlueshift

SummarySummary

Stars are large bodies of plasma held Stars are large bodies of plasma held together by gravitytogether by gravity

The Hurtzsprung-Russel relates The Hurtzsprung-Russel relates brightness to temperature of starsbrightness to temperature of stars

There are three main classifications of There are three main classifications of starsstars

There are three models for the origin of There are three models for the origin of the universe, the leading model is the big the universe, the leading model is the big bang theorybang theory

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