Star Characteristics in Astronomy Grade 9.ppt

characteristics of the stars

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Stars CharacteristicsStars Characteristics

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Learning Objectives:Learning Objectives:
Classify stars based on their Classify stars based on their
characteristics ( color, temperature, characteristics ( color, temperature,
size, brightness and composition).size, brightness and composition).
Predict how a star’s color relates to its Predict how a star’s color relates to its
temperature.temperature.

3. What are the characteristics of a star?What are the characteristics of a star?
Stars differ in…Stars differ in…
MassMass
SizeSize
TemperatureTemperature
ColorColor
Luminosity/Luminosity/
BrightnessBrightness

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Mass and Composition Mass and Composition
A star is a massive ball of gases, A star is a massive ball of gases,
mainly hydrogen and helium.mainly hydrogen and helium.
Bigger stars have more mass, greater Bigger stars have more mass, greater
gravity and are hotter than smaller gravity and are hotter than smaller
stars.stars.

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Star SizeStar Size
The physical dimension of a star, ranging The physical dimension of a star, ranging
from small dwarfs stars to massive from small dwarfs stars to massive
supergiants.supergiants.
Large Stars: Giants or Super GiantsLarge Stars: Giants or Super Giants
Medium Stars: Main Sequence (the Sun)Medium Stars: Main Sequence (the Sun)
Small Stars: White Dwarf or Neutron Small Stars: White Dwarf or Neutron

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7. Star EnergyStar Energy
The enormous pressure and heat in a The enormous pressure and heat in a
star’s star’s corecore converts matter into converts matter into energyenergy..
This reaction is called This reaction is called nuclearnuclear fusionfusion
In nuclear fusion, In nuclear fusion, hydrogenhydrogen atoms fuse atoms fuse
to form to form heliumhelium atoms. atoms.
During each step of the process, During each step of the process, massmass
is lost and is lost and energyenergy is released. is released.

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Star Energy cont.Star Energy cont.
The The energyenergy released causes the star (Sun) to released causes the star (Sun) to
shineshine and gives the star its high and gives the star its high temperature.temperature.

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Star TemperatureStar Temperature
The heat of a star, measured in degrees The heat of a star, measured in degrees
Celsius or Kelvin. Hotter stars emit blue or Celsius or Kelvin. Hotter stars emit blue or
white light, while cooler stars appear red or white light, while cooler stars appear red or
orange.orange.
Stars in the sky show tinges of different Stars in the sky show tinges of different
colorscolors which reveal the stars’ which reveal the stars’ temperaturestemperatures. .
Blue: hottestBlue: hottest
Yellow: medium temperatureYellow: medium temperature
Red: coolestRed: coolest

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Star ColorStar Color
The color of a star indicates its surface The color of a star indicates its surface
temperature. Blue stars are the hottest, while temperature. Blue stars are the hottest, while
red stars are the coolest.red stars are the coolest.

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Classification of StarsClassification of Stars
ColorColor Surface Surface
temp (ºC)temp (ºC)
ExamplesExamples Spectral ClassSpectral Class
BlueBlue Above 30,000Above 30,000 10 Lacertae10 Lacertae OO
Blue-whiteBlue-white
10,000 – 30,00010,000 – 30,000
Rigel, SpicaRigel, Spica BB
WhiteWhite
7,500 – 10,0007,500 – 10,000 Vegas, SiriusVegas, Sirius AA
Yellow-whiteYellow-white 6,000 – 7,5006,000 – 7,500 Canopus, Canopus,
ProcyonProcyon
FF
YellowYellow 5,000 – 6,0005,000 – 6,000
Sun, CapellaSun, Capella GG
OrangeOrange 3,500 – 5,0003,500 – 5,000 Arcturus, Arcturus,
AldebaranAldebaran
K K
RedRed
Less than 3,500Less than 3,500Betelgeuse, Betelgeuse,
AntaresAntares
MM

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Star Luminosity/BrightnessStar Luminosity/Brightness
The amount of light a star emits. It The amount of light a star emits. It
depends on both its size and temperature. depends on both its size and temperature.
A bigger, hotter star is generally brighter A bigger, hotter star is generally brighter
than a smaller, cooler one. than a smaller, cooler one.
The The brightnessbrightness of a star depends upon of a star depends upon
the the distancedistance and its and its luminosity.luminosity.
Apparent Brightness/Magnitude: Apparent Brightness/Magnitude: a star’s a star’s
brightness as seen from Earth.brightness as seen from Earth.
Absolute Brightness/Luminosity: Absolute Brightness/Luminosity: the the
actual brightnessactual brightness

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Stop and ThinkStop and Think
If person A has a pen flashlight and If person A has a pen flashlight and
person B has a mega flashlight and person B has a mega flashlight and
both were standing at the front of the both were standing at the front of the
classroom, which light would appear classroom, which light would appear
brighter?brighter?
If person A (pen light) stood in the classroom and If person A (pen light) stood in the classroom and
person B (mega light) stood at the baseball fields person B (mega light) stood at the baseball fields
across the street, which light would appear brighter?across the street, which light would appear brighter?
You cannot tell by looking in the sky how bright a star You cannot tell by looking in the sky how bright a star
truly is. The farther away the star is, the less bright ittruly is. The farther away the star is, the less bright it
will appear.will appear.

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The Hertzsprung-Russell DiagramThe Hertzsprung-Russell Diagram
A chart used by astronomers to A chart used by astronomers to
classify stars based on their classify stars based on their
brightness, temperature, and brightness, temperature, and
evolutionary stage.evolutionary stage.

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The Hertzsprung-Russell DiagramThe Hertzsprung-Russell Diagram
An H-R diagram plots stars according An H-R diagram plots stars according
to their to their luminosityluminosity and and temperaturetemperature..

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Location of Stars on an H-R DiagramLocation of Stars on an H-R Diagram

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Star MassStar Mass
Position on H-R depends on Position on H-R depends on massmass
The larger the amount of The larger the amount of massmass in a star, in a star,
the more the more luminousluminous it is. it is.

Giants: Giants: moremore mass, mass, moremore luminous luminous
Dwarfs: Dwarfs: lessless mass, mass, lessless luminous luminous
During its lifetime a star will evolve on the During its lifetime a star will evolve on the
H-R diagram depending on its mass. H-R diagram depending on its mass.

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1. Stars are primarily composed of hydrogen and helium.
2.A star’s mass does not affect its temperature or brightness.
3.The Sun is classified as a white dwarf.
4.Blue stars are the hottest, while red stars are the coolest.
5.Nuclear fusion in a star's core converts hydrogen into
helium, releasing energy.
6.A star’s brightness depends only on its size.
7.The Hertzsprung-Russell diagram classifies stars based on
their brightness and temperature.
8.Apparent brightness is how bright a star truly is, regardless
of distance.
9.The larger the mass of a star, the more luminous it tends to
be.
10.White dwarfs are smaller and less luminous than red
supergiants.