stars
TRANSCRIPT
Stars
What is a star?
• The objects that heat and light the planets in a system
• A star is a ball of plasma held together by its own gravityoNuclear reactions occur in stars (H
He)oEnergy from the nuclear reactions is
released as electromagnetic radiation
Characteristics of Stars
• DISTANCEoMeasured in light-years
The distance which a ray of light would travel in one year
About 6,000,000,000,000 (6 trillion) miles186,000 miles per second
Characteristics of Stars
• Magnitude (brightness)oA measure of brightness of celestial
objectsSmaller values represent brighter objects
than larger values oApparent magnitude
How bright a star appears to be from Earth oAbsolute magnitude (luminosity)
How bright a star actually is
Characteristics of Stars
• Temperature & ColoroThe color of a star indicates the T of the
staroStars are classified by T
Decreasing T (bright to dim)O, B, A, F, G, K, M [Oh Be A Fine Girl, Kiss Me ]
http://www.seasky.org/cosmic/sky7a01.html
Hertzsprung-Russell Diagram
http://www.dustbunny.com/afk/stars/lifecycle/hrdiagram.gif
Main Sequence Stars
• A major grouping of stars that forms a narrow band from the upper left to the lower right when plotted according to luminosity and surface temperature on the Hertzsprung-Russell diagram
Types of StarsClassification
Red2,000 – 3,500 KM
Orange3,500 – 5,000 KK
Yellow5,000 – 6,000 KG
Yellow-white6,000 – 7,500 KF
White 7,500 – 10,000 KA
Blue-white10,000 – 30,000 KB
Blue20,000- 60,000 KO
ColorTemperatureClass
http://www.answers.com/topic/stellar-classification
Life Cycle of Stars
http://hea-www.cfa.harvard.edu/CHAMP/EDUCATION/PUBLIC/ICONS/life_cycles.jpg
Life Cycle of Stars
• Begin their lives as clouds of dust and gas called nebulae
• Gravity may cause the nebula to contract• Matter in the gas cloud will begin to condense
into a dense region called a protostar• The protostar continues to condense, it heats up.
Eventually, it reaches a critical mass and nuclear fusion begins.
• Begins the main sequence phase of the star• Most of its life is n this phase
Life Cycle of Stars
Life span of a star depends on its size.• Very large, massive stars burn their fuel much
faster than smaller stars• Their main sequence may last only a few
hundred thousand years• Smaller stars will live on for billions of years
because they burn their fuel much more slowly• Eventually, the star's fuel will begin to run
out.
Life Cycle of Stars
• It will expand into what is known as a red giant
• Massive stars will become red supergiants• This phase will last until the star exhausts
its remaining fuel• At this point the star will collapse
Life Cycle of Stars
• Most average stars will blow away their outer atmospheres to form a planetary nebula
• Their cores will remain behind and burn as a white dwarf until they cool down
• What will be left is a dark ball of matter known as a black dwarf
Life Cycle of Stars
• If the star is massive enough, the collapse will trigger a violent explosion known as a supernova
• If the remaining mass of the star is about 1.4 times that of our Sun, the core is unable to support itself and it will collapse further to become a neutron star
Life Cycle of Stars
• The matter inside the star will be compressed so tightly that its atoms are compacted into a dense shell of neutrons. If the remaining mass of the star is more than about three times that of the Sun, it will collapse so completely that it will literally disappear from the universe. What is left behind is an intense region of gravity called a black hole
Life Cycle of Stars
http://www.seasky.org/cosmic/sky7a01.html