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Star Light, Star Bright
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3 Factors that determine the brightness of a star
Temperature Hotter the star the brighter the star Blue…..white……..yellow…….orange…….….red HOTTEST COOLEST
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Size Larger the star Brighter the Star
Smaller the star Dimmer the Star
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Distance Closer the star Brighter the star
Further the star Dimmer the star
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Brightness Key Terms Luminosity Apparent Magnitude Absolute Magnitude
How much light energy is coming from the surface Apparent Magnitude How bright it appears to be due to distance Absolute Magnitude How bright it is if its distance was a parsec or 33 light years Parallax The shift of closer stars against a background of farther stars as the Earth goes around the Sun
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Luminosity Definition- actual or true brightness of a star
Total amount of energy given off Dependent on 2 things: Temperature Size 6000K 6000K 6000K 10,000K More luminous since more energy More luminous since more surface area
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Apparent Magnitude Definition- how bright a star appears when seen from earth System developed where a number is assigned to a star based on brightness Scale is basically based on powers of 10 difference A +2 is 10 times as bright as a 3, +100 times as bright as a +4 Smaller # Brighter the star Bigger # Dimmer the star Sun -28 , Full Moon -11, Polaris 7 Hubble can see +28
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Absolute Magnitude Definition- brightness of a star as if all stars were seen from the same distance Earth Earth Sun- average star, Abs. Mag of +4.8 (less luminous, looks brighter because closer) Rigel- orion, Abs, Mag. of -6.4 (more luminous, further away) To Determine: apparent magnitude and distance to earth
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Moving Stars? Parallax- the apparent change in position of a star due to the movement of observer Finger: left/right
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Life Cycle of a Star
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Life Cycle of Stars Planetary Nebula White Dwarf Red giant 1 Main
Sequence Star Nebula Protostar Red supergiant 2 Supernova Black Hole Neutron Star
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Life Cycle Introduction
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Step 1: Initiation Stars are born in nebulae (huge clouds of gas and dust) Nebula begin to condense when an outside force, such as shock wave, acts upon it
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Step 2: Pre-star A protostar forms when a part of the nebula contracts, shrinks, and pressure and internal temperature increases Protostar begins to glow where nebula is contracting
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Step 2 contd: A star is born
As contraction, temperature, density, and pressure increase protostar gets larger and brighter Center becomes so hot fusion begins Once fusion begins, a star is born TRUE STAR
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Step 3: Teenager star Internal temperature hot enough to start fusion at center said to be a main sequence star Sun is an example Each protostar will turn into one main sequence star 90% of stars are main sequence stars Vary in surface temperature and absolute magnitude
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Fate determined by Size
If a normal size star (Sun) follows path 1 If star is a GIANT follows path 2
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Path 1
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Step 4: Middle-aged star
Red giant- very bright, once an average star, but is now close to end of life Has expanded to many times its original size (heat causes it to expand) Hydrogen core has turned to helium and eventually to carbon Our sun will become a red giant star in about 5 billion years
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Star like our sun begins to die
Star begins to die when its core temperature rises to a point where fuel is used up A carbon-oxygen core forms Eventually the gases at a star’s surface begin to blow away in abrupt bursts Resulting glowing halo is called a planetary nebula
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Death of a star like our sun
atoms no longer fuse, fuel is used up Outer gases escape leaving the core which collapses and shrinks Heat still present but will continue to escape for about a billion of years White Dwarf- small, very dense, hot star at the end of its life, mostly carbon with nuclear cores depleted (about the size of earth but heavier)
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Path 2
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Step 4: Middle-aged massive star
Supergiant- largest known type of star can be as large as our solar system rare but exists In a massive star, hydrogen is fused more quickly and fusion continues until a iron nuclei is formed
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Death of a Supergiant Supernova- exploding star Elements are used up very quickly and eventually runs out of fuel Collapse of the core produces a shock wave that blasts the star’s outer layers into space producing a supernova
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Option A after a supernova
When neutron star is first formed, it spins very rapidly and gives off radio waves After a massive star “goes supernova” it leaves behind its core (called a neutron star) -Neutron Star- small, dense star made of neutrons
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Option B after a supernova
Black Hole- a star that collapses How do we know they exist? Pulls gases off nearby stars, as gas is pulled into this “nothing space” x-rays are emitted from the gas as molecules are pulled in
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Cycle continues Star is born from great clouds of gas and dust
Stars mature, grow old, and die As a star dies, it makes new clouds of dust gas and dust where new stars can begin to form More massive a star, the shorter its life
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Hertzsprung-Russell Diagram
Graph that compares temperature and absolute magnitude (brightness)
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The Hertzsprung-Russell Diagram (H-R diagram)
Cool and bright Bright Hot and bright Cool and dim Hot and dim Sun Dim Hot Cool
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Supergiants Hot and bright Cool and bright Giants Main sequence White Dwarfs Cool and dim Hot and dim
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