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StarsStars
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 gravity–Nuclear reactions occur in stars (H He)
–Energy from the nuclear reactions is released as electromagnetic radiation
Characteristics of Stars
• DISTANCE–Measured in light-years
•The distance which a ray of light would travel in one year
•About 6,000,000,000,000 (6 trillion) miles
•186,000 miles per second
How Do we Measure Stars Distance?
Parallax- the apparent change in position of an object when you look at it from different places
Parallax
The closer the star is to Earth, the larger the shift will be. (No good past a 1000 Light Years.
Characteristics of Stars
• Magnitude (brightness)–A measure of brightness of
celestial objects• Smaller values represent brighter
objects than larger values –Apparent magnitude
• How bright a star appears to be from Earth
–Absolute magnitude (luminosity)• How bright a star actually is
Characteristics of Stars
• Temperature & Color–The color of a star indicates the Temperature of the star
–Stars are classified by Temperature• Decreasing Temperature (bright to dim)
• O, B, A, F, G, K, M [Oh Be A Fine Girl, Kiss Me ]http://www.seasky.org/cosmic/sky7a01.html
Types of StarsClassification
Class Temperature Color
O 20,000- 60,000 K Blue
B 10,000 – 30,000 K Blue-white
A 7,500 – 10,000 K White
F 6,000 – 7,500 K Yellow-white
G 5,000 – 6,000 K Yellow
K 3,500 – 5,000 K Orange
M 2,000 – 3,500 K Red
Size Video
• http://www.youtube.com/watch?v=LsgKp_Vf6wI&list=PL9D64A9B670629B26&index=12
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
Hertzsprung-Russell Diagram
http://www.answrs.com/topic/stellar-classification
Life Cycle of Stars
http://hea-www.cfa.harvard.edu/CHAMP/EDUCATION/PUBLIC/ICONS/life_cycles.jpg
Life Cycle
• Stars begin their lives as clouds of dust and gas called Nebulae (Greek for cloud)
• Gravity may cause the nebula to begin to contract
Life Cycle
• 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.
Star Nurseries
Life Cycle
• After nuclear fusion begins, stars begin the main sequence phase.
•Most of its life is in this phase
The Sun: the nearest Main Sequence star to the Earth. This is an X-ray image from the Yohkoh satelite.
Logo for the Subaru car company.
Pleiades or the 7 Sisters
Life Cycle
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
• 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
BETELGEUSE –RED GIANT• Only a few million
years old, Betelgeuse is already dying. Astronomers predict that it's doomed to explode as a soon, within 1,000 years or so, an event that will be spectacular for Earth's future inhabitants. (Conceivably, it's already happened as Betelgeuse is 640 light-years away!)
Hubble image of Betelgeuse a Red Supergiant
Life Cycle
• 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
Image of Sirius A and Sirius B taken by the Hubble Space Telescope
Life Cycle
• 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
Crab Nebula
Life Cycle
• 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
