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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 Stars
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
Classifying StarsClassifying Stars
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)
Classifying StarsClassifying Stars
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
Evolution of StarsEvolution of Stars
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
Evolution of StarsEvolution of Stars
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..
Evolution of StarsEvolution of Stars
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..
Evolution of StarsEvolution of Stars
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.
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
ConstellationsConstellations
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
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
Measurements in SpaceMeasurements in Space
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
Measurements in SpaceMeasurements in Space
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
Galaxies and The UniverseGalaxies and The Universe
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
Galaxies and The UniverseGalaxies and The Universe
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)
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