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Astronomy
Stars, Galaxies, and the Universe
Tools of Ancient Astronomy
Tools of Modern Astronomy
The Electromagnetic
Spectrum
The electromagnetic spectrum is a list of
electromagnetic waves placed in order
of increasing energy.
Tools of Modern Astronomy
Astronomers use tools that focus different types of
electromagnetic energy to study distant objects in space.
What are these tools called?
Telescopes
Radio Wave Telescopes
World’s Largest Radio
Telescope: Arecibo
Facility in Puerto Rico
measures 1000 feet
across, 167 feet
deep, and 20 acres.
Can we hear radio waves?
No, radios convert electromagnetic
radiation to sound energy we can
hear.
Infrared Telescopes
The United
Kingdom Infrared
Telescope in
Hawaii.
How does your body interpret infrared
radiation?
Heat
Visible Light Telescopes
The Hubble
Telescope is a
light telescope
that floats in
space!
Why would Hubble Telescope pictures be
clearer than ones taken from Earth’s surface?
There is no atmosphere
to look through.
Ultraviolet Telescopes
The Hopkins
ultraviolet
telescope being
released by the
Space Shuttle.
Why would an ultraviolet telescope need
to be in space?
Earth’s atmosphere blocks ultraviolet
radiation.
X-Ray Telescopes
The Chandra X-Ray
Telescope
What else do we use x-rays for?
Medical diagnosing like to see if you
have a broken bone.
Gamma Ray Telescopes
The gamma-ray
telescope on Mt.
Hopkins, Arizona.
Besides stars, what else emits
gamma-rays?
Nuclear Explosions.
Characteristics of Stars
 1) brightness, which astronomers
describe in terms of magnitude or
luminosity;
 2) color;
 3) surface temperature;
 4) size;
 5) mass (amount of matter)
Magnitude and luminosity
 A star's brightness as viewed from
Earth is its apparent magnitude.
 Luminosity is the rate at which a star
emits energy.
Color and Temperature
 A star's color depends on its surface
temperature.
 Dark red stars  2500 K.
 Bright red stars  3500 K
 Yellow stars (e.g. the Sun)  5500 K.
 Blue stars  10,000 to 50,000 K
Size and Mass
 Astronomers measure the size of stars
in terms of the sun's radius.
 Astronomers express the mass of a star
in terms of the solar mass, the mass of
the sun.
 The mass of the sun is written out as 2
followed by 30 zeros.
Nebula to Globule
 New stars form from large, cold clouds of
dust and gas.
 Stars usually start to form in a nebula, a
cloud of interstellar hydrogen gas and dust.
 When the gas and dust are forced together,
they form a slowly rotating globule.
Gravitational forces survive through gas
pressure and the globule starts to collapse,
then the cooling occurs and the spin
increases.
Globule to Star
 The globule starts to change into a
protoplanetary disk (which could also
become a planet) and a central core (which
will become a star).
 The core of the protoplanetary disk starts to
increase in temperature.
 When fusion starts to begin, that's when a
protostar has been formed. If the
temperature reaches about
27,000,000,000°F, nuclear fusion begins,
then stars start to form.
A Star is Born
 When stars are born they come in different
sizes and their color range from blue to red.
 The size of a star depends on the gas and
dust that have been collected during the
birth of the star.
 The color of the star depends on the surface
temperature of the star.
 The more mass a star starts out with the
hotter and brighter it will be.
Lives of Stars
 Throughout a star's life, it tries to fight
the inward pull of the force of gravity.
 Stars live different lengths of time
depending on the size.
 The hotter and brighter a star is, the
shorter their lives are.
Long Live the Stars!
 For example, the sun would live for
about 10 billion years while a star 20
times bigger than that will only live for
10 million years.
A Star’s Final Hours
 When a star's supply of hydrogen runs
out, it eventually dies.
 The death of a star depends on what
type of star it is and the size of the
star.
 Stars will either become a black dwarf,
a neutron star or a black hole,
depending on the size of a star.
The Evolution of Stars
 Main Sequence Phase - Longest phase of a
star’s life - hydrogen is burning in core fusion energy and gravity are balanced
 Red Giant Phase - all hydrogen in the core
has become helium - gravity becomes
stronger and the star begins to collapse
 White Dwarf Phase - shells are blown away remaining core is carbon and oxygen
 Black Dwarf Phase - core has become so cold
that it is difficult to see - the star has died
Supernova
 That’s not the end!
 The collapsing core shrinks to a size
about 6 miles in diameter
 Then it “rebounds” outwards in less
than a second, sending all of its gases
and dust to be used again for the birth
of a new star.
What’s left behind?
 The gravity of the collapsing star that
is left behind becomes a Black Hole
 a region of space whose gravitational
force is so strong that nothing can
escape from it.
 A black hole is invisible because it
traps even light.
What’s at the center of a
Black Hole?
 All its matter is located at a single
point in its center.
 This point, known as a singularity, is
much smaller than an atomic nucleus.
Black Hole
A X-ray telescope picture of a
black hole.
Star Systems
 A star system is a small number of
stars which orbit each other bound by
gravitational attraction.
 A large number of stars bound by
gravitation is generally called a star
cluster or galaxy.
Galaxies
 A galaxy is a massive, gravitationally
bound system consisting of stars, an
interstellar medium of gas and dust,
and dark matter all orbiting a common
center of mass.
 Our galaxy is called the Milky Way
The Universe
 The Universe is defined as everything that
physically exists: the entirety of space and
time, all forms of matter, energy and
momentum, and the physical laws and
constants that govern them.
 Astronomical observations indicate that the
universe is 13.73 ± 0.12 billion years old[1]
and at least 93 billion light years across.
History of the Universe
 According to the prevailing scientific
theory, the universe has expanded
from a gravitational singularity known
as the Big Bang, a point in space and
time at which all the matter and
energy of the observable universe were
concentrated.
Resources
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