The%20History%20of%20Astronomy

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The History of Astronomy
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Prehistoric Astronomy

• Introduction
• People of antiquity most likely began studying
  the heavens many thousands of years ago.
• Early astronomical observations certainly
  revealed the obvious
• Rising of the Sun in the eastern sky and its
  setting in the west
• Changing appearance of the Moon
• Eclipses
• Planets as a distinct class of objects different
  from the stars

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The Roots of Astronomy

• Already in the stone and bronze ages, human
  cultures realized the cyclic nature of motions in
  the sky.
• Monuments dating back to 3000 B.C. show
  alignments with astronomical significance.
• Those monuments were probably used as calendars
  or even to predict eclipses.

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____________________________
Constructed 3000 1800 B.C

• Alignments with locations of sunset, sunrise,
  moonset and moonrise at summer and winter
  solstices
• Probably used as calendar.

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Early Ideas of the Heavens

• Ancient___________________ Astronomers
• Through the use of models and observations, they
  were the first to use a careful and systematic
  manner to explain the workings of the heavens
• Limited to naked-eye observations, their idea of
  using logic and mathematics as tools for
  investigating nature is still with us today
• Their investigative methodology is in many ways
  as important as the discoveries themselves

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Ancient Greek Astronomers

• Unfortunately, there are no written documents
  about the significance of stone and bronze age
  monuments.
• First preserved written documents about ancient
  astronomy are from ancient Greek philosophy.
• Greeks tried to understand the motions of the sky
  and describe them in terms of mathematical (not
  physical!) models

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Ancient Greek Astronomers

• Models were generally wrong because they were
  based on wrong first principles, believed to be
  obvious and not questioned

1. ______________________________Universe Earth at
   the Center of the Universe.
2. __________________________________ Motions of
   all celestial bodies described by motions
   involving objects of perfect shape, i.e.,
   spheres or circles.

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Aristotle (384-322 BCE)

• the Greek philosopher ________________________prop
  osed that the heavens were literally composed of
  55 concentric, crystalline spheres to which the
  celestial objects were attached and which rotated
  at different velocities
• He also thought that the Earth was the center of
  the Solar System.the ____________________________
  _____model
• Remember that Geo means__________________________
  .

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Aristotles Universe
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____________________(276-197 BCE)

• Eratosthenes was a Greek mathematician and
  geographer. He developed a map of the world.
• He estimated _____________________________________
  ___________of the Earth.
• He did that sometime around 240 B.C. He knew that
  there was no shadow at the bottom of a well in
  the town of Syene on the summer solstice. That
  meant that the Sun must be straight overhead in
  Syene on that day. He measured the length of the
  shadow of a tall tower in Alexandria on the same
  day. He also measured the distance between Syene
  and Alexandria. With this information, he was
  able to calculate the circumference of the Earth.

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____________________________ (85-165AD)

• Ptolemy, Alexandrian (Greek) mathematician,
  geographer, and astronomer, developed the most
  sophisticated mathematical model of the motions
  of the Solar System based upon the geocentric
  (__________________________________) model and
  the principle of perfect circular motion.
• Most of _____________________Astronomy comes from
  this man.

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Claudius Ptolemy (85-165AD)

• His model was quite complex in order to follow
  the details of planetary motions, requiring
  circles (______________________) upon off
  centered circular orbits. His major astronomical
  work explains how epicycles work to
  produce_______________________.

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Epicycles
Introduced to explain retrograde (westward)
motion of planets
The Ptolemaic system was considered the standard
model of the Universe until the Copernican
Revolution.
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Modern Astronomy

• We will study the findings of 5 modern
  astronomers that have made significant impacts on
  the understanding of astronomy
• These guys are
• _____________________________________
• _____________________________________
• _____________________________________
• _____________________________________
• _____________________________________

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The Copernican Revolution
Nicolaus Copernicus (1473 1543) Heliocentric
Universe (Sun in the Center)
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_______________________________ (Copernicus,
1473-1543)

• Copernicus studied mathematics and astronomy in
  Italy, but spent his life as a physician,
  attorney and church administrator.
• By Copernicus' time, the Ptolemaic model could no
  longer reproduce the observed planetary
  positions.
• Copernicus developed a____________________ model
  of the Solar System which retained the notion of
  perfect circular motion, but placed the Sun at
  the center and established the proper order of
  the planets outward from the Sun.

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Copernicus new (and correct) explanation for
retrograde motion of the planets

• Retrograde (westward) motion of a planet occurs
  when the Earth passes the planet.

This made Ptolemys _________________unnecessary.
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____________________________- An Observer

• Tycho Brahe was a prominent scholar and
  aristocrat in Denmark in the mid-late 1500's
• He made a huge number of observations of the
  stars and planets, all with the naked eye
• Even without a telescope, he was very accurate in
  his measurements
• Also recorded the appearance of___________________
  ___________________________________________
• The Tycho supernova remnant is still visible today

Tycho (1546-1601)
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____________________________ (1594 1642)

• Invented the modern view of science Transition
  from a faith-based science to an
  observation-based science.

• Greatly improved on the newly invented telescope
  technology. (But Galileo did ___________________in
  vent the telescope!)

• Was the first to meticulously report telescope
  observations of the sky to support the
  _________________________________ Model of the
  Universe.

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Galileo Galilei

• Using ____________________of his own design and
  manufacture, Galileo also made many discoveries
  in astronomy sunspots on the Sun and craters and
  mountains on the Moon.
• The so called _________________________" which
  orbit Jupiter -- Io (with the volcanoes), Europa,
  Callisto and Ganymede.
• rings of Saturn.
• the phases of_________________________.

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Major Discoveries of Galileo

• Moons of Jupiter
• (4 Galilean moons)

• Rings of Saturn

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Major Discoveries of Galileo (2)

• Surface structures on the moon first estimates
  of the height of mountains on the moon

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Major Discoveries of Galileo (3)

• Sun spots (proving that the sun is not perfect!)

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Major Discoveries of Galileo (4)

• Phases of Venus (including full Venus),
  proving that Venus orbits the sun, not the Earth!

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Galileo Galilei

• Galileo's observations suggested that the heavens
  were as ______________" as the Earth that other
  objects in the Solar System have______________
  which orbit around them, and that Venus passes
  through a full range of phases. These
  observations led him to the conclusion that
  the_____________ Model of the Solar System is
  preferable to the ___________________Model.

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Galileo Galilei

• They were in direct contradiction to the
  world-view taught by the __________Church, and he
  was called before the Italian inquisition
  in_______________. Galileo was forced
  to___________________ his work, and was sentenced
  to _________________for the remainder of his
  life.

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Astronomy in the Renaissance

• __________________________________ (1571-1630)
• Upon Tychos death, his data passed to Kepler,
  his young assistant
• Using the very precise Mars data, Kepler showed
  the orbit to be an ellipse
• Keplers Three Laws
• Planets move in elliptical orbits with the Sun at
  one focus of the ellipse
• The orbital speed of a planet varies so that a
  line joining the Sun and the planet will sweep
  out equal areas in equal time intervals
• The amount of time a planet takes to orbit the
  Sun is related to its orbits size, such that the
  period, P, squared is proportional to the
  semimajor axis, a, cubed
• P2 a3
• where P is measured in years and a is measured
  in AU

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Keplers Laws of Planetary Motion

1. The orbits of the planets are ________________with
   the sun at one focus.

Eccentricity e c/a
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Kepler's ________________Law

• Kepler also noticed that the planets sweep out
  equal areas in their orbit over equal times
• Notice that this means the planet must speed up
  and slow down at different points
• If it takes the same amount of time to go through
  A as it does C, at what point is it moving
  faster?
• C, when it is closest to the Sun

Kepler's 2nd Law An imaginary line connecting
the Sun to any planet sweeps out equal areas of
the ellipse over equal intervals of time.
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Kepler's __________________ Law

• Finally, Kepler noticed that the period of
  planet's orbit squared is proportional to the
  cube of its semi major axis
• This law allowed the orbits of all the planets to
  be______________________________________________
• It also allowed for the prediction of the
  location of other possible planets

Kepler's 3rd Law Simplified
NOTE In order to use the equation as shown, you
must be talking about a planet in the Solar
System, P must be in years, and a must be in A.U.
!!!
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Kepler's _____________ Law - Examples

• Suppose you found a new planet in the Solar
  System with a semi major axis of 3.8 A.U.
• A planet with a semi major axis of 3.8 A.U. would
  have an orbital period of 7.41 years

years
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Kepler's _________Law - Examples

• Suppose you want to know the semi major axis of a
  comet with a period of 25 years
• A planet with an orbital period of 25 years would
  have a semi major axis of 8.55 A.U.

A.U.
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Astronomy in the Renaissance

• Johannes Kepler (continued)
• Consequences of Keplers laws
• Second law implies that the closer a planet is to
  the Sun, the ________________________________it
  moves
• Third law implies that a planet with
  a_________________ average distance from the Sun,
  which is the semimajor axis distance, will take
  longer to ______________the Sun
• Third law hints at the nature of the force
  holding the planets in orbit
• Third law can be used to determine the semimajor
  axis, a, if the period, P, is known, a
  measurement that is not difficult to make

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Isaac Newton Birth of Astrophysics

• ____________________________________(1642-1727)
  was born the year Galileo died
• He made major advances in mathematics, physics,
  and astronomy
• He pioneered the modern studies of motion,
  optics, and gravity and discovered the
  mathematical methods of calculus
• It was not until the 20th century that Newtons
  laws of motion and gravity were modified by the
  theories of relativity

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Isaac Newton

• Kepler's Laws were a revolution in regards to
  understanding planetary motion, but there was no
  explanation _________________they worked
• That explanation would have to wait until Isaac
  Newton formulated his laws of_____________________
  __ and the concept of_______________
• Newton's discoveries were important because they
  applied to actions on Earth and in space
• Besides motion and gravity, Newton also developed
  calculus

Newton (1642-1727)
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Some terms

• _____________________________________ the push
  or pull on an object that in some way affects its
  motion.
• ___________________________________ the force
  which pulls you toward the center of the Earth
  (or any other body).
• ______________________________ the tendency of
  an object to keep moving at the same speed and in
  the same direction
• ________________ basically, the amount of matter
  an object has
• The difference between speed and velocity
• These two words have become identical in common
  language, but in physics, they mean two different
  things
• Speed is just magnitude of something moving (25
  km/hr)
• Velocity is both the magnitude and direction of
  motion (35 km/hr to the NE)

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Newton's_______________ Law

• Newton's first law states An object
  at_____________________ will remain at rest, an
  object in uniform motion will stay in motion -
  __________________________acted upon by an
  outside force
• This is why you should always wear a seat belt!

Outside Force
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Newtons Laws of Motion (1)
An astronaut floating in space will continue to
float forever in a straight line unless some
external force is accelerating him/her.
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Newton's _________________Law

• Acceleration is created whenever there is a
  change in velocity
• Remember, this can mean a change in magnitude
  AND/OR direction
• Newton's Second Law states When a
  __________________________acts on a body, the
  resulting acceleration is equal to the force
  divided by the object's mass
• Notice how this equation works
• The _______________________the force, the larger
  the acceleration
• The ________________________the mass, the larger
  the acceleration

or
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Newtons Laws of Motion (2)

1. The acceleration a of a body is inversely
   proportional to its mass m, directly
   ______________________ to the net force F, and in
   the same direction as the net force.

a F/m ? F m a
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Newton's Third Law

• Newton's Third Law states For every action,
  there is an equal and opposite reaction
• Simply put, if body A exerts a force on body B,
  body B will react with a force that is equal in
  magnitude but opposite direction
• This will be important in astronomy in terms of
  gravity
• The Sun pulls on the Earth and the Earth pulls on
  the Sun

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Newtons Laws of Motion (3)

1. __________________________________________________
   ________________________________________

M 70 kg
V ?
The same force that is accelerating the boy
forward, is accelerating the skateboard backward.
m 1 kg
v 7 m/s
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Newton and the ______________- Gravity

• After formulating his three laws of motion,
  Newton realized that there must be some force
  governing the motion of the planets around the
  Sun
• Amazingly, Newton was able to connect the motion
  of the planets to motions here on Earth through
  gravity
• __________________________ is the attractive
  force two objects place upon one another

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____________________________

• Any two bodies are attracting each other through
  gravitation, with a force proportional to the
  product of their masses and inversely
  proportional to the square of their distance

Mm
F - G
r2
(G is the Universal constant of gravity.)
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The Gravitational Force

• _______________is the gravitational constant
• G 6.67 x 10-11 N m2/kg2
• m1 and m2 are the masses of the two bodies in
  question
• r is the distance between the two bodies

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Understanding Orbital Motion

• The universal law of gravity allows us to
  understand orbital motion of planets and moons

Example

• Earth and moon attract each other through
  gravitation.

Dv

• Since Earth is much more massive than the moon,
  the moons effect on Earth is small.

v
v

• Earths gravitational force constantly
  accelerates the moon towards Earth.

Moon

• This acceleration is constantly changing the
  moons direction of motion, holding it on its
  almost circular orbit.

Earth
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Orbital Motion (2)

• In order to stay on a closed orbit, an object has
  to be within a certain range of velocities

Too slow gt Object falls back down to Earth
Too fast gt Object escapes Earths gravity
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Keplers Third Law Explained by Newton

• Balancing the force (called _____________________
  _________) necessary to keep an object in
  circular motion with the gravitational force ?
  expression equivalent to Keplers third law,

Py2 aAU3
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____________________________
Einstein (1879 1955) noticed that Newtons laws
of motion are only correct in the limit of low
velocities, much less than the speed of light.
? Theory of Special Relativity
Also, revised understanding of gravity
? Theory of General Relativity
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Other Noteables

• 18th Century, William Herschel discovered Uranus,
  a new planet beyond Jupiter. Barely visible with
  the unaided eye, Herschel made the observation
  with his telescope .
• 1910 Harlow Shapley estimated the size of the
  Milky Way.
• Einstein (1905) developed the Theory of Special
  Relativity, based upon the idea that light
  travels at the same speed in all frames of
  reference. Modified Newton's Theory of Gravity by
  developing the General Theory of Relativity
  (1916).
• 1930 Clyde Tombaugh discovered Pluto.

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Big Notable

• 1924 ____________________________established that
  the Andromeda nebula and other "spiral nebulae"
  are star systems like the Milky Way at great
  distances.
• 1929 Hubble Milton Humason discovered that the
  Universe is expanding.

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The Electromagnetic Spectrum

• Wavelength/frequency/energy

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Light and Other Forms of Radiation

• The__________________________________

In astronomy, we cannot perform experiments with
our objects (stars, galaxies, ).
The only way to investigate them, is by analyzing
the light (and other radiation) which we observe
from them.
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What is it?

• The electromagnetic spectrum is the complete
  spectrum or continuum of light including radio
  waves, infrared, visible light, ultraviolet
  light, X-rays and gamma rays
• An electromagnetic wave consists of electric and
  magnetic fields which vibrates thus making waves.

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__________________________

• Properties of waves include speed, frequency and
  wavelength
• Speed (s), frequency (f) and wavelength (l) are
  related in the formula l x f s
• All light travels at a speed of 3 s 108 m/s in a
  vacuum

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Wavelength

• The distance from one wave crest to the next
• Radio waves have longest wavelength and Gamma
  rays have shortest!

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Wavelength, Frequency and Energy

• Since all light travels at the____________________
  _______, wavelength and frequency have an
  indirect relationship.
• Light with a short wavelength will have a high
  frequency and light with a long wavelength will
  have a low frequency.
• Light with short wavelengths has high energy and
  long wavelength has low energy

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______________________

• Low energy waves with ____________________________
  _____wavelengths
• Includes FM, AM, radar and TV waves
• Wavelengths of 10-1m and longer
• Low frequency
• Used in many devices such as remote control
  items, cell phones, wireless devices, etc.

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_________________________

• Longer than_____________, shorter than light and
  infrared
• Wavelength 1 x 10 - 4 m to 1 x 10-1 m
• First used in radar, now used in communication,
  medicine and consumer use (microwave ovens)

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___________________________

• Invisible electromagnetic waves that are detected
  as_____________________
• Can be detected with special devices such as
  night goggles
• Used in heat lamps
• Higher energy than microwaves but lower than
  visible light

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________________

• The portion of the electromagnetic spectrum that
  human eyes can detect
• ROY G BIV (red, orange, yellow, green, blue,
  indigo, violet)
• _______________________________is the lowest
  frequency and ___________________________ is the
  highest frequency

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Electromagnetic Spectrum

• Visible Spectrum Light we can see
• Roy G. Biv Acronym for Red, Orange, Yellow,
  Green, Blue, Indigo, Violet..
• Red is the lowest frequency and violet is the
  highest frequency.

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_______________________

• Higher energy than light waves
• Can cause __________________________and blindness
  in humans
• Used in tanning beds and sterilizing equipment

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___________________________

• High energy waves
• Used in medicine, industry and astronomy
• Can cause cancer

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__________________________

• _____________________ energy
• Blocked from Earths surface by atmosphere

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How light or electromagnetic radiation is used in
Astronomy

• Astronomers use a tool called a spectroscope to
  separate starlight into its colors in this way,
  they can tell what a star is made of, its
  temperature, luminosity and so on
• Astronomers can look at astronomical objects at
  different wavelengths

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Doppler Effect
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__________________________________________________
______.

Sound Each circle represents the crests of sound
waves going in all directions from the train
whistle. The circles represent wave crests coming
from the train at different times, say, 1/10
second apart. If the train is moving, each set of
waves comes from a different location. Thus, the
waves appear bunched up in the direction of
motion and stretched out in the opposite
direction.
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Doppler Shift for Light
We get the same effect for light as for sound.
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Doppler Effect

• The Doppler effect is the apparent change in the
  _______________________of a wave motion when
  there is relative motion between the source of
  the waves and the observer.
• The apparent change in frequency ?f experienced
  as a result of the Doppler effect is known as the
  Doppler shift.
• The value of the Doppler shift increases as the
  relative velocity v between the source and the
  observer increases.
• The Doppler effect applies to all forms of waves.

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Summary of the Doppler Effect
The Doppler effect can be summarized
qualitatively
The observed frequency of sound is increased
when the source and observer are approaching each
other and is decreased when they are receding
from each other.
Or mathematically,
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Blue Shift ..Red Shift
If we see a ________________________.this means
that an object is moving closer to us in space. A
good example is the Andromeda Galaxy..one day it
will collide with the Milky Way. This is because
the wavelengths of light are getting shorter,
thus shifting towards the blue side of the
spectrum. If we see a _______________________..th
is means that an object is getting further away
from us. We see a lot of red shift in the
universe. This information is one piece of
evidence that the universe is expanding. This
means that the light wave is getting longer,
shifting to the red side of the spectrum.
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Measuring Rotational Velocity
Doppler shift can be used to tell us how fast an
object is rotating As an object rotates, light
from side rotating toward us is blueshifted -
light from side rotating away from us is
redshifted. Spectral lines appear wider - the
faster it rotates, the wider are the spectral
lines.
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Earth Based Telescopes
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History

• invented by Dutch lens maker in 1608
• Galileo small 30X scope
• Observed the moon and began the modern age of
  Astronomy where measurement was more important
  than philosophy

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How a telescope works

• gathers light through the objective (mirror or
  lens)
• bigger is better because it gathers more light
• ability to see faint objects increases
  proportionally with the square of the radius of
  the objective
• focuses light
• viewed through an eyepiece (changing the eyepiece
  changes the magnification)
• magnification is the ratio of the focal length of
  the objective to the focal length of the eyepiece

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General types of telescopes

• _____________________________________ (objective
  is a lens)
• _____________________________ (objective is a
  mirror)

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Refractors (glass lens)
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Advantages and Disadvantages

• Easy to use and reliable
• Excellent for lunar, planetary and binary star
  observing especially in larger apertures.
• High contrast images with no secondary mirror or
  diagonal obstruction.
• Sealed optical tube reduces image degrading air
  currents and protects optics.

• More expensive per inch of aperture
• Heavier, longer and bulkier than equivalent
  aperture Newtonians and catadioptrics.
• Small apertures
• Less suited for viewing small and faint deep sky
  objects.
• Color aberration due to colors of light bending
  different amounts.

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Reflectors (mirror)
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Advantages and disadvantages

• Lowest cost per inch of aperture
• Reasonably compact and portable up to focal
  lengths of 1000mm.
• Excellent for faint deep sky objects such as
  remote galaxies, nebulae and star clusters.
• Reasonably good for lunar and planetary work.
• Low in optical aberrations.

• Open optical tube design allows image-degrading
  air currents and air contaminants
• More fragil
• Large apertures (over 8") are bulky, heavy and
  tend to be expensive.
• Slight light loss due to secondary obstruction
  when compared with refractors.

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Not everything is _____________
www.yorku.ca/eye/spectrum.gif

• Many modern day telescopes do not use visible
  light to collect images.
• Radio telescopes, x-ray telescopes and infrared
  (IR) telescopes have become a staple of modern
  day astronomy, producing some amazing images.

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Radio Astronomy
Recall Radio waves of l 1 cm 1 m also
penetrate the Earths atmosphere and can be
observed from the ground. Remember this a very
_______________________of the Electromagnetic
Spectrum
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Radio Telescopes
Large dish focuses the energy of radio waves onto
a small receiver (antenna)
Amplified signals are stored in computers and
converted into images, spectra, etc
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Infrared Astronomy
Most ________________________is absorbed in the
lower atmosphere.
However, from high mountain tops or high-flying
air planes, some infrared radiation can still be
observed.d.
NASA infrared telescope on Mauna Kea, Hawaii
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X-Ray Astronomy

• X-rays are completely ______________in the
  atmosphere.

• X-ray astronomy has to be done from
  ________________.

X-rays trace hot (million degrees), highly
ionized gas in the Universe.
NASAs Chandra X-ray Observatory
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Chandra

• Launched in 1999, designed to observe such
  objects as __________________and quasars.
• Provided measurements of the age of the universe,
  which is estimated to be about 12-14 billion
  years old.

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Gamma-Ray Astronomy
Gamma-rays most ____________electromagnetic
radiation
traces the most violent processes in the Universe
The Compton Gamma-Ray Observatory
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Compton Gamma Ray (1991 - 2000)
The Compton Gamma Ray Observatory was the second
of NASA's Great Observatories. Compton, at 17
tons, was the heaviest astrophysical payload ever
flown at the time of its launch on April 5, 1991
aboard the space shuttle Atlantis. Compton was
safely deorbited and re-entered the Earth's
atmosphere on June 4, 2000.
__________________________________________________
_________
June 4, 2000, NASA deliberately deorbited the
telescope, allowing most of it to burn up during
reentry and what was left of it to crash safely
into the Pacific Ocean.
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Hubble Space Telescope Cont
Every__________ minutes, Hubble completes a spin
around Earth, moving at the speed of about
_________________per second (8 km per second)
fast enough to travel across the United States in
________________minutes. As it travels, Hubble's
mirror captures light and directs it into its
several science instruments. Hubble has made
breakthroughs in Cosmology, Planetary Science and
Galactic Science Hubble cannot get good images
of Mercury because it is too______________ to the
sun.
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Hubble's Data Pipeline