Title: Stars
1Stars
2What 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
3 A. Characteristics of Stars
- 1. 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
4A. Characteristics of Stars
- 2. Magnitude (brightness)
- A measure of brightness of celestial objects
- Smaller values represent brighter objects than
larger values - a. Apparent magnitude
- How bright a star appears to be from Earth
- b. Absolute magnitude (luminosity)
- How bright a star actually is
5A. Characteristics of Stars
- 3. Temperature Color
- The color of a star indicates the T of the star
- Stars 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
6Hertzsprung-Russell Diagram
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7B. 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
8Types 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
9http//www.answers.com/topic/stellar-classificatio
n
10C. Life Cycle of Stars
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11C. 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
12C. 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.
13C. Life Cycle of Stars
- It will expand into what is known as a
- RED GIANT
- Massive stars will become a
- RED SUPERGIANT
- This phase will last until the star exhausts its
remaining fuel - At this point the star will collapse
14Life 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
15Life 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
16Life 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
17Life Cycle of Stars
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