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Essential Question:
Chapter 28 Stars and Galaxies
28.1 Closer look at Light
 Light is a form of electromagnetic radiation, which is energy that
travels in waves.
 Waves of energy travel at 300,000 km/sec (speed of light
 Ex: radio waves and x-rays
 Electromagnetic waves do not need a medium to travel, they
travel through space
 Electromagnetic waves emitted by an object indicated what
elements are present and its motion
 Electromagnetic radiation waves are arranged into a
continuum call the electromagnetic spectrum.
 Wide range of wavelengths
 long wavelengths with low frequencies at one end, short
wavelengths with high frequencies at the other end
 wavelength measured crest to crest/trough to trough
 frequency the number of that crests of the same wavelength
that pass a point in one second.
 Scientists study the visible light portion of the electromagnetic
spectrum.
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Summary:
spectra of stars allow for astronomers to learn about the star’s
elements and motion.
Spectra studied using a spectrascope
Essential Question:
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Summary:
Three types of visible spectra
 Continuous spectrum: unbroken band of colors, emitting all
colors of visible light
 glowing solids, such as a light bulb filament
 glowing liquids, molten iron
 hot, compressed gases inside a star
 Emission spectrum: unevenly spaced lines of different colors,
emitting light of only some wavelengths
 glowing thin gases
 every element has its own unique emission spectrum,
element’s finger print
 Absorption spectrum: dark lines that cross a continuous
spectrum.
 forms when light from a glowing object pass through a
cooler gas which absorbs some wavelengths
 can determine what is present in the cooler gas by
comparing emission and absorption spectrum
Doppler Effect is the apparent change in the wavelength of radiation
or sound due to relative motion between the object and the receiver.
Doppler effect applies to light as well as sound.
Shift of the emission spectra can indicate if the object is moving
towards or away from Earth
Shift towards the red end of the visible light spectrum, object moving
away Earth – redshift
Essential Question:
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Shift towards the blue end of the visible light spectrum, object moving
towards Earth - blueshift
 Doppler effect determined that the universe is expanding
Telescopes
 Optical Telescopes – gather far more light than an unaided eye and
magnify imagers
 Reflecting Telescopes
 Uses one lens at back to gather and focus light
 Image reflected on to a small mirror and then the eye
piece
 Refracting Telescopes
 Uses two lenses
 Lens at the front gathers light
 Eyepiece magnifies image
 Radio Telescopes
 Technical term for really big satellite dishes
 Use to detect energy waves at frequencies lower than visible
light
 Other
 Detects energy waves at frequencies higher than visible light
 Usually satellites in space
 Gamma ray
 Background radiation
 X-ray
 Hubble (infrared)
28.2 Stars and Their Characteristics
 Observation of stars has been going on for over 5000 years
 The grouping of stars are called Constellations
 Constellations
 human grouping of stars
 only appear together as viewed from Earth from a different
angle they do not look like the constellation
 Grouped together due to looking like they all have the same
brightness (apparent magnitude)
Summary:
Essential Question:
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Summary:
Constellations will change shape over shape over thousands
of years due to the universe expanding
 Some constellations have been around for thousands of years
other were recently conceived
 Move across the sky from east to west (though Earth rotates
west to east)
 Big Dipper and Little Dipper two of the best know
constellations point to the North Star
North Star
 Current north star is called Polaris
 Sits directly over the north pole
 Does not move to the naked eye
 Very powerful tool for navigation
 Due to Precession, Polaris will not always be the “North Star”
Circumpolar Constellations – constellations around the north star
 Create star trails
evidence for Earth’s rotation
 North star appears fixed in the sky as Earth rotates
 star trails from circumpolar constellations rotate
counterclockwise around the north star
 Circumpolar constellations seem to never set from some
northern hemisphere latitude
Distances to stars and other objects in space
 Unit of measurements on Earth are not sufficient for space
measurements
 Astronomical Unit (AU) is used for the distance from Earth to
the Sun (150 million kilometers)
 Light Year is the distance light travels in one year (9.5 trillion
kilometers)
 It is a distance measurement
 Example - 4.2 light-years means that the light we see
has been traveling for 4.2 years before we can see it
(4.2 X 9.5 trillion km)
 Parallax change in an object’s direction due to a change in the
observer’s position
 Parsec short for “parallax second” equal to 3.258 light-years.
Essential Question:
The further the object is
from the viewer, the less
the parallax shift.
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Summary:
Stars
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Elements
 Hydrogen ~69%
 Helium ~29%
 Heavier elements ~2%
 No two stars have the same proportions of elements
 light that radiates is dependent on composition and
temperature, this differs in every star
 Star spectrum is its fingerprint
Mass, Size and Temperature
 Stars vary greatly in masses, size, and temperature
 Cannot observe directly so we are estimating what the mass
might be
 Gravitational effect on bodies around the star help
with estimating its mass
 Star mass is expressed as multiples of the mass of our
Sun (which has a stellar mass of 1)
 Size varies more than mass
 Smallest stars are smaller than Earth
 Largest have diameters more than 2000 times that of
our Sun
Essential Question:
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Stars differ even more in density
 Betelguese is about one ten-millionth of our Sun
 One star is so dense that one teaspoon would weight
more than a ton on Earth
 Temperature of stars vary
 Stars have different colors which indicate different
temperatures
 Cool stars are red in color
 Mid-temp are yellower in color
 Hot stars are blue in color
 Astronomers group stars by temperature and color into
spectral classes.
Star Brightness
 Actual brightness of a star is Luminosity
 Dependent on size and temperature
 Distance from Earth is not a factor
 If two stars are the same size the hotter star would be
more luminous
 Apparent magnitude is how bright a star appears to an observe
on Earth
 Does not factor in distance from earth
 Absolute magnitude is the measure of how bright a star would
be is all stars were the same distance from Earth (10 parsec)
28.3 Life Cycle of Stars
See foldable for Star life cycle and HR Diagram
Summary:
Essential Question:
28.4 Galaxies and the Universe
Galaxies:
 The universe is everything that exists.
 The observable universe is everything we can observe.
 Astronomers are not sure how old the universe is since the
light from the beginning has not yet reach us. The estimate is
between 10-20 billion years
 Galaxies are hard to separate from stars without a telescope.
 Hazy patches of light which when viewed through a telescope
reveals thousands to billions of stars.
 Astronomers estimate there are 50- 100 billion galaxies in the
observable universe.
 No two galaxies are the same, however, they are classified based on
shape.
 There are three classifications
 spiral (ex. Milky Way)
 elliptical are near spherical to lens-shape
 irregular (ex. The two Magellanic Clouds )
Origin of the Universe
 Big Bang Models (Theory) – explains history of the universe from a
tiny fraction of a second after it came into being up to the present
 Best explanation for how the universe came to being
 Developed due to observations of stars, galaxies and other
objects with telescopes and experimenting with matter on
Earth
 Approximately 10-20 billion years ago all matter in the
universe existed in an incredibly hot and dense state, from
which it expanded and cooled slowly condensing into stars and
galaxies.
 It is expanding at a very slow rate and is still expanding today
Summary:
Essential Question:
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Summary:
Evidence for the Big Bang Model:
 The universes apparent expanstion, distance between galaxies
and groups of galaxies seems to be increasing with time.
 Edwin Hubble’s discovery of the redshift in the spectra of
galaxies supports the expansion of the universe
 Discovery of radiation called cosmic background radiation
apparently left over from the universe’s beginning.
 Continues to be tested and examined to seek further evidence
to support it
 Some astronomers are considering alternative ways the
universe has reached its present state.
It is impossible to know for certain how the universe began
as long as the Big Bang Model survives (passes) crucial tests, it
remains the best explanation for the origin of the universe
If it were to ever fail a test, then astronomers will have to look for a
new theory/model