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Astronomy
Origin and Fate of the Universe
Hubble’s Law
Hubble’s law basically says that the universe is
expanding.
That is to say that the space between galaxies
is increasing; with greater distance is
greater speed.
Closer galaxies are moving apart slower than
those galaxies farther away.
HOW DO WE KNOW?
Hubble’s Evidence =
Spectra
Spectra are the colors produced when
the wavelengths of light are separated.
The Doppler Effect
The Doppler effect is a change of light or
sound wavelengths as a source moves toward
or away from the observer.
Red shift = source is moving away so
wavelengths stretch into longer wavelengths
Blue shift = source is moving closer so
wavelengths squeeze into shorter
wavelenghts.
BLUE TO YOU.
Deep Space Phenomena
Based on the observed rates of expansion it is
believed that about 15-20 billion years ago
all matter was concentrated into one
“primeval atom”.
This “atom” exploded and sent all matter and
space expanding =
BIG BANG
What are Stars?
• Star = a hot, glowing sphere of gas
that produces energy by fusion (of
hydrogen molecules).
–Some stars produce more energy
therefore they are hotter.
How Do Stars Form?
• Nebula = a cloud of dust and
gas where stars are born.
–Here gravity pulls particles
together and nuclear fusion starts
at 10,000,000 oC and a star is born.
The Horse Head Nebula
More Horse Head Nebula Shots
Types of Stars
Depending on the conditions within a nebula,
different types of stars can form:
Red Giants = big, “cool” stars
White Dwarfs = “small”, hot stars
How Are Stars Classified?
• Stars are classified by:
–Temperature
–Color
–Luminosity / Brightness
Stars are Classified by Temperature
and Color.
• HOT
BLUE
COLD
WHITE
YELLOW ORANGE
RED
BROWN
What is a Main Sequence Star?
What is a Main Sequence Star?
• The H-R diagram represents a pattern that
was discovered that allows stars to be
compared by brightness and color.
• The majority of stars are found in a band
stretching diagonally across the diagram
called the “Main Sequence”.
• Stars start out in the Main Sequence and as
the core cools, they move onto the giant
category. A few rare stars are bigger and
brighter and become supergiants.
Stars are Classified by Brightness
• Actual brightness
is how bright a star
really is.
• Actual brightness
does not change, it
is an absolute
value.
• Example: a 40
watt light bulb is
actually converting
40 watts of energy
into light.
• Apparent brightness
is how bright a star
looks from earth.
• Apparent brightness
changes depending
on distance from
earth and viewing
conditions
(atmosphere).
• Example: a 40 watt
light bulb 10 feet
away appears
brighter than a 40
watt bulb 100 feet
away.
…And After Stars are Born?
Life Cycle of a Star
Neutron Stars
A neutron star results when a white dwarf
collapses and the pressure converts the
electrons into atomic nuclei to produce
neutrons.
The outer portion of a neutron star may
explode with incredible force producing a
supernova.
What is a Supernova?
• Supernova is when the core of a
star collapses and the outer portion
explodes. This is the “death of a
star”.
• What remains when a star dies out
depends on the mass of the star.
– Material from the explosion may form
a new star called a pulsar – a rapidly
spinning neutron star.
– The most massive stars collapse into
black holes.
What is a Black Hole?
• Black Hole = the most dense thing
known to exist in the universe. The
gravity of a black hole is so great
that even light can not escape the
pull of a black hole.
The massive
density of
Black Holes
creates a
gravitational
force that
pulls in
anything that
comes within
reach: the
reach of this
force is
called the
event
horizon.
The fate of
objects that
enter a
Black Hole
is still
uncertain.
?