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Bell Work:
Name 3 things all
Electromagnetic Waves
have in common.
Chapter 21
Stars, Galaxies,
and
the Universe
Electromagnetic
Radiation
Energy that can travel through space
The Electromagnetic Spectrum
Ranks Electromagnetic Waves based on their _______.
Visible Light –
Electromagnetic Radiation you can see
Spectrum of visible light  ROY G. BIV
Telescopes
Instruments that collect and focus light and other forms
of electromagnetic radiation
Used to make distant objects appear larger & brighter
First used to study space by Galileo
2 Main Types:
Optical
Non-Optical
Optical vs Non-Optical
Optical Telescopes
Non-Optical Telescopes
Uses lenses or mirrors to collect
& focus VISIBLE light
Collect and focus different types
of electromagnetic radiation
2 Types:
Refracting Telescopes
Reflection Telescopes
3 Types:
Radio Telescopes
Ultraviolet Telescopes
Infrared Telescopes
Source of Radiation:
Stars, Planets, Moons
Uses:
Study size , composition, and
movement of stars and galaxies
Refracting Telescope
Uses Convex lenses to gather
and focus light
Convex Lens –glass curved so
that the middle is thicker than
the edges
Tw0 Convex Lenses – one at each
end of long tube
Large LensGathers Light  larger = more
light it can collect
Smaller LensMagnifies the image
Reflecting Telescopes
1st one built in 1668 by Isaac Newton
Uses a curved mirror to collect and
focus light
Uses two lenses like the refracting
Today, the largest optical
telescopes are all reflecting
telescopes
Radio Telescopes
Used to Detect RADIO waves in
space
Curve, reflecting surfaces
Concentrates faint radio waves
from space onto small antennas
Larger = more radio waves it can
collect
Source of Radiation
Galactic Centers, Stars, Black
Holes
Uses:
Find Black Holes
Map Galactic Centers
Bell Work:
What is the difference between
an optical and non-optical
telescope?
Ultraviolet Telescopes
Source of Radiation:
Distant stars, Clouds of dust
and gas
Uses:
To map sources and analyze
their composition
Infrared Telescopes
Source of Radiation:
Stars, Galaxies
Uses:
To study planets around other
stars
This image of the Pinwheel
Galaxy combines data in the
infrared, visible, ultraviolet and
x-rays from four of NASA’s
space telescopes.
Development of Telescopes
1897 – Yerkes Telescope in Wisconsin
Largest refracting telescope ever built  collects most light
1931 – Accidental discovery of Radio Waves by Karl Jansky
1963 – Arecibo- radio telescope built in natural bowl in ground
1980 – Very Large Array –set of 27 radio telescopes in New Mexico
1990 – Hubble Space Telescope – Reflecting telescope above Earth’s
atmosphere; very detailed images in visible light
1992 - Compton
1999 – Chandra – X-ray telescope; very detailed
2003 – Spitzer – 0.86 meter in diameter infrared telescope
ObservatoryBuilding that contains one or
more telescopes
Many located on Mountaintops
or in Space. Why?
Earth’s atmosphere makes
objects in space look blurry
Sky on mountaintops is
clearer & not brightened by
city lights
Telescopes in SpaceMost radiation is blocked by
Earth’s atmosphere
To detect these  Scientists
have placed telescopes in space
The Keck observatory
domes atop Mauna Kea
Constellations
An imaginary pattern
of stars in the sky.
Different cultures
gave different names
to the constellations
Used by astronomers
to locate objects in
the night sky
Characteristics of Stars
Scientists classify stars based on their:
Color & Temperature:
Reveals the surface temperature
Hottest stars  blue
Coolest Stars  red
Size:
Vary greatly in size
Larger than the sun  Giant or Supergiant stars
Size of Earth White dwarf stars
Chemical Composition:
Most is 73% Hydrogen, 25% Helium (Similar to sun)
Spectrograph - determines the elements in stars
Brightness:
Depends on size, temperature , & distance from Earth
Apparent Brightness vs. Absolute Brightness
Bell Work:
Name the 4 things Scientists
look at to classify a star.
Measuring the Distance to Stars
Astronomers use lightyear units to measure
distances between the
stars
Astronomers use parallax to
measure distance.
Parallax – apparent change
in position of an object when
you lo0k at it from different
places
The Hertzsprung-Russell Diagram
Graphs made by two Scientists,
Hertzsprung and Russell
Graphs of surface temperatures
and absolute brightness of stars
to see how they were related
Main Sequence –
Diagonal area on HertzsprungRussell
location of more than 90 percent
of stars, including the sun
Surface temp increase AS absolute
brightness increases
 hot blue star on left
 cooler red stars on right
Brightest stars  top
(Giant & Supergiant)
Cooler, not as bright stars 
bottom
(white dwarfs
Life Cycle of Stars
A star is born when nuclear fusion starts.
Stars are born IN a nebula - huge clouds
of dust and gas  gravity pulls together
enough gas and dust a protostar is
formed
Stars grow old and begin to run out of
fuel
 the core shrinks; outer layers
expand, cool, and become less
bright; it is now called a red giant
or a super giant (depending on the
initial mass of the star)
 After running out of “fuel” it
will become either a black dwarf,
neutron star, or black hole
Images from the Hubble
Space Telescope showing
the life cycle of stars.
The Lifecycle of a star depends on
its original Mass.
How long can a star live?
About 10 million to 200 billion
years
White Dwarf
Blue-white core of a star left
behind and cools
No fuel left but faintly glows
Black Dwarf
A White dwarf that no longer
“glows”
Supernova
Explosion of a dying HIGH mass
star
Neutron stars
Small, dense remains of a high
mass star after a supernova
Black holes
Object with gravity so strong that
nothing, even light, can escape
Formed when the most massive
stars collapse and die
Star Systems & Clusters
Most stars are members of groups of two or more stars 
star systems
Binary stars  star systems with two stars
Eclipsing binaries star system in which one star periodically
blocks the light from another; one may also appear dimmer
from time to time
Star Clusters  larger groupings stars belong to
All stars in a cluster formed from the SAME nebula at about
the SAME time and are about the SAME distance from Earth
Open cluster  loose, disorganized, only a few thousand stars
Globular cluster  large groupings of older stars
Galaxies – huge group of single stars, star systems,
star clusters, dust and gas held together by gravity
3 main categories:
1. Spiral –
bulge in middle with
spiral arms; “pinwheel”
Arms contain young stars,
dust, & gas
2. Elliptical –
round or flattened balls
mainly old stars due to
little, or almost no, gas or
dust
3. IrregularNo regular shape
Typically smaller
Many bright, young stars
The Milky Way A spiral galaxy where our solar system is located
The Universe:
collectively describe the planets, stars, galaxies, and any other
matter that exists in space
The part of the universe that can be observed is believed to be 46
billion light years across and is expanding constantly.
How did the Universe form?
Astronomers believe that our universe formed in an instant, enormous
explosion billions of years ago – The Big Bang Theory
Hubble’s Law –
states that the farther away a galaxy is, the faster it is moving away
from us
Supports the Big Bang theory
What is the Future of the Universe?
Many Theories:
1. Continue to expand until stars run out of fuel  universe
becomes cold and dark
2. gravity will begin to pull galaxies back together 