Download Notes- Stars

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 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
Characteristics of Stars
• Magnitude (brightness)
– A measure of brightness of celestial
objects
– 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 Temp of
the star
http://www.seasky.org/cosmic/sky7a01.html
The Lives of Stars
• A star’s life history depends on its mass.
After a star runs out of fuel, it becomes a
white dwarf, a neutron star, or a black hole.
The Lives of Stars
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
Biggest Black Hole
3.5 Billion
Light Years
away
18 billion
times the
size of the
sun!
Black Holes
• Gravity is so strong that not even light can
escape!
• Often at the center of galaxies!
• A Galaxy is a huge group of stars, dust,
and gas held together by gravity
• Milky way is a spiral galaxy, but galaxies
can also be irregular or elliptical in shape
Black holes
• http://youtu.be/cW7BvabYnn8
Scientific Notation
• Scientists use scientific notation (powers of ten)
to describe really small numbers or really large
numbers.
• The decimal gets moved until there is only 1
number before the decimal
• If you move the decimal to the right, the
exponent is negative (RS= Right Subtract, Red
Sox)
• If you move the decimal to the left, the exponent
is positive (LA= Left Add, LA Dodgers)
Examples:
• 0.0000467 = 4.67 x 10-5
• 0.000000089 = 8.9 x 10-8
• 5,677 = 5.677 x 103
• 2,340,000,000 = 2.34 x 109
Expand the Numbers
• 8.67 x 10-6 = 0.00000867
• 9.2 x 107 = 92,000,000
• 1.17 x 104 = 11,700
• 4.4 x 10-5 = 0.000044
Scientific Notation
• Practice Problem
• The sun takes about 220,000,000 years to revolve once
around the center of the galaxy. Express this length of
time in scientific notation.
• 2.2 X 108 years
Scientific Notation
• Practice Problem
• The bright star Deneb is about 3,230 light-years from
Earth. Express this number in scientific notation.
• 3.23 x 103 light-years