glowing ball of gas in space which generates energy through nuclear fusion in its core closest star...
TRANSCRIPT
STARS
Star
Glowing ball of gas in space which generates energy through nuclear fusion in its core
Closest star to Earth is the Sun
Light Years
Most of the universe is empty space even though it appears it is full of stars
Stars are very far apart Light-year
Distance that light travels in a vacuum in a year
Approximately 9.5 trillion kilometers Closest star to the sun is about 4.3 light-
years away
Light year
Parallax
Scientists cannot measure distances to stars directly
Apparent change in position of an object with respect to a distant background is called a parallax
Astronomers measure the parallax of nearby stars to determine their distance from earth
Accurately measures stars that are within a few hundred light-years
Parallax
Properties
Color Size Brightness Other important properties
Chemical composition Mass
Color and Temperature
Estimate temperature by color Hottest stars (temperatures above
30,000 K) Blue
Relatively cool stars (temperature ~ 3000 K) Red
Temperature 5000 to 6000 K Yellow
Color and Temperature
Brightness
Brightness of a star does not depend on closeness to earth
Brighter stars may be farther away than stars that appear dim
Apparent brightness Brightness of a star as it appears from Earth Apparent brightness decreases as its distance
from you increases Absolute brightness
How bright a star really is
Size and Mass
Estimate the diameter and calculate the volume
No direct way of finding the mass of an isolated star
Calculate the mass by observing gravitational interactions of stars in pairs
Composition
Spectrograph Instrument that spreads light from a hot
glowing object into a spectrum Each star has its own spectrum Elements within stars absorb light at
different wavelengths Absorption lines
Set of dark lines that show where light has been absorbed
Observations have shown that stars have fairly similar compositions
Absorption lines
Hertzpung-Russel Diagram
H-R diagram Used to estimate the sizes of stars and their
distances and to infer how stars change over time
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
90% of all stars are found here
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
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 in 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
The matter inside the star will be compressed so tightly that its atoms are compacted into a dense shell of neutrons.
Life Cycle of Stars
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