Download The Doppler effect

Unit 5 - Space Exploration
Lesson 1 - For Our Eyes Only
A frame of reference is a set of axes of any kind that is used
to describe the positions or motion of things. For example, the
equator and the prime meridian are the axes for the frame of
reference used to locate positions on Earth (latitude and
longitude).
Ancient peoples watched the motions of celestial bodies (Sun,
Moon, stars, and planets). They noticed that stars make
unchanging patterns in the sky. These patterns looked like
objects which people grouped and named. These groupings are
called constellations. Ex. Orion, Great Bear - Ursa Major.
 On each successive day, a given star rises and sets four
minutes earlier than the day before. This means that over
time, different stars are in the night sky. Since each month
has its own set of stars in the night sky, people developed
the ability to predict the changing of the seasons – helped
in the creation of calendars.
Sky Co-ordinates
 A celestial bodies’ location in the sky was measured by
using two co-ordinates measured in degrees. The first
angle is measured clockwise from north. This is called
the azimuth. Next measures the angle above the
horizon. This is called the altitude.
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 Angles used to specify the co-ordinates of a celestial
body are called altitude-azimuth co-ordinates.
(p. 359)
 The co-ordinates for each body change depending on
the time of the reading.
 Our ability to measure the positions of bodies in the sky
has always depended upon technological devices. An
astrolabe is a device used to measure the altitude. A
compass is used to measure an object’s azimuth.
 To track the actual motion of each celestial body we use
the stars as the frame of reference instead of Earth.
This is because we are looking for motions in the sky
that are different from the big motion caused by Earth’s
rotation.
The Earth-Sun-Centered Models
 Ancient peoples believed that the stars circled around
Earth. This led to an Earth-centered or geocentric model
of the universe, which lasted almost 2000 years. (Started
by Greek philosopher Aristotle).
 In the early 1500s, polish astronomer Nicholas
Copernicus proposed that the Sun was fixed, and a
rotating Earth revolved around it. This is known as the
Sun-centered or heliocentric model of the universe.
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Stronger Eyes and Better Numbers
 A telescope is used to magnify objects at great distances.
It was invented by Hans Lippershey (Dutch), in 1608. A
simple telescope consists of an objective lens and an
ocular lens.
 An objective lens is the large one at the front of the
telescope. The ocular lens is the eyepiece through which
you look.
 Later that century, Galileo Galilei, improved the telescope
and used it to make celestial observations that required
new explanations. Unlike scientists before him, Galileo
insisted that any model of the universe should be backed
up by actual and careful observations.
 Resolving power is the fineness of detail the telescope
can produce of the object in view. This depends on the
diameter of the objective lens – the larger the diameter
the greater or finer the detail.
Refractors and Reflectors
 Many types of telescopes have been invented since
Galileo’s time.
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 Refracting telescopes have a lens for their objectives and
reflecting telescopes have a mirror (See Fig. 5.14 p.
370).
Lesson 2 – Johannes Kepler
 In 1609, Johannes Kepler, showed that the planetary
orbits were elliptical rather than circular. An ellipse is a
figure that looks like a squashed circle.
 By using a combination of mathematics and data gathered
by astronomer Tycho Brahe over a period of 20 years of
observations, Kepler also figured out the shape and scale
of the entire known solar system.
Universal Gravitation
 Newton stated the law of universal gravitation, which
provided an explanation for the planets’ elliptical orbits.
 According to Newton’s law there is a gravitational force
of attraction between all masses in the universe. When
no forces act on an object, it will move in a straight line at
a constant speed.
 The planets are always moving but the force of gravity of
the Sun results in the elliptical path.
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The Spectroscope: New Meanings in Light
 Isaac Newton passed a beam of sunlight through a prism
to produce a spectrum of colors. It showed that normal
white light is made up of all colors (ROY G BIV).
 If you pass a beam of light through a narrow slit before
sending it through a prism, the resulting spectrum shows
much finer detail.
 A spectroscope is a device that produces this kind of
focused spectrum.
 Fraunhofer (1820s), a German optician, used a
spectroscope to observe the Sun’s spectrum. He noticed
hundreds of dark lines in the Sun’s spectrum (also called
the solar spectrum). These dark lines are called spectral
lines.
Spectroscopy: The Science of Color
 Gustav Kirchoff and Robert Bunsen (German physicist
and chemist) heated various chemicals to incandescence
and examined their light through a spectroscope. They
discovered that not all of the colors of the rainbow were
present – each spectrum was a series of color lines with
black spaces between them. Each spectrum was unique
and could be used to identify the element.
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 Spectroscopy is the study of spectra. There are three
types of spectra:
1. Continuous - rainbow
2. Emission or Bright line
3. Absorption or Dark line (see p. 377)
Diffraction Grating
 A device made of thousands of closely spaced slits is
called a diffraction grating. It produces a better spectrum
than a prism.
 Modern spectroscopes use diffraction gratings instead of
prisms to split the light into spectra.
 Astronomers use spectral analysis to identify the gases
on the Sun (and to a lesser extent on stars because of
distance).
The Doppler effect
 You have probably noticed that the siren on an ambulance
sounds different as the vehicle approaches, passes and
then moves away from you. The siren’s change in pitch is
called the Doppler effect and is caused by the change in
the sound’s wavelength.
 As the vehicle approaches you the wave gets compressed
resulting in higher pitch and the wave gets stretched as it
moves away resulting in lower pitch.
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 The Doppler effect can be used to measure the speed and
direction of light-emitting objects such as stars. If the star
is going away from you, its spectral lines will be red
shifted – longer wavelength part (red end). If it’s moving
toward the lines will be blue shifted.
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Lesson 3 - Bigger
and Smarter Telescopes
 In 1773 Sir William Herschel, an English astronomer,
built a large reflecting telescope. With this telescope, he
discovered the planet Uranus.
 Today, with the use of computers, it is possible to
combine images from two or more telescopes.
Adaptive Optics
 Stars twinkle because of the Earth’s motion and the
bending (refraction) of light by the atmosphere. The
technology that cancels out the twinkling effect is called
adaptive optics.
Distance – Measuring with Triangulation
 Triangulation is a method of measuring distance
indirectly by creating an imaginary triangle between an
observer and an object whose distance is to be estimated
(See Fig.5.30&5.31 p.387&388).
 Astronomers use triangulation to measure distances to
celestial objects.
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 Astronomers use the diameter of Earth’s orbit as the
baseline for triangulating on a nearby objects. The angle
between the baseline and the star’s position is measured
in January and July, for example.
 The nearest star to Earth is Proxima Centauri and it is
more than 272,000 astronomical units (AU) from the
Sun. One astronomical unit is the distance from Earth to
the Sun (150 million km).
 Astronomers use light-years to measure interstellar
distances. A light-year represents the distance that light
travels in one year (about 63,240 AU). On this scale,
Proxima Centauri is 4.28 light-years away.
What Channel Is That?
 Light isn’t the only kind of radiation coming from the
stars – light is just one form of electromagnetic
radiation. The electromagnetic spectrum is made up of
radio waves, microwaves, infrared radiation (heat), visible
light, ultraviolet radiation, X-rays, and gamma rays. (See
Fig. 5.33 p. 393).
 Radio astronomy uses radio waves to study the
composition of stars. The first radio telescope (antenna)
was built in 1932 by Karl Jansky and later perfected by
Reber (made a parabolic dish).
 “Listening” to the stars through the radio telescope would
be like tuning a radio between channels. Reber would
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hear hissing static. The hiss would become louder when
he tuned in to an area in space that was giving off large
amounts of radio waves – the bright radio objects. In
our solar system the Sun is the brightest of all the radio
objects, and Jupiter is the second brightest.
 Radio astronomers wanted to identify their strong sources
with objects they had seen with optical telescopes. This
was impossible at first because the radio images had such
low resolutions. As the radio telescope improved,
astronomers could make these optical connections.
 If two or more radio telescopes are connected together,
their signals can be combined using a computer. It’s like
seeing with many eyes instead of one. This method is
called interferometry. The most accurate set of
connected telescopes in the world is the Very Large
Array (VLA) in New Mexico.
 Today telescopes can be connected without wires. This is
called very long baseline interferometry (VLBI). VLBI
produces images 100 times as detailed as the largest
optical telescopes.
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Lesson 4 - Above
the Atmosphere
 The Earth’s atmosphere prevents astronomers from
getting a clear view of the universe. Thus, astronomers
are sending telescopes into space using rockets and
computers.
 A rocket is a tube that contains combustible materials in
one end and a payload in the other end and moves by the
action, reaction principle (Newton’s Third Law of
Motion: For every action there is an equal and opposite
reaction).
 The fuel used in a rocket creates exhaust that comes out
of the rocket. The speed at which it leaves is called the
exhaust velocity. The greater the exhaust velocity the
greater the rocket’s range.
 To increase the velocity of the exhaust, liquid fuel is used
instead of solid fuel, and the fuel is kept in several
compartments. As the fuel is used up in that compartment,
it is dropped off to make the rocket lighter – a staged
rocket.
 To send rockets throughout the universe, scientist use a
technique called gravitational assist. Gravitational assist
uses the gravity of a planet to change the speed and/or
direction of a rocket. (Fig. 5.42 p. 402).
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Clarifying Images
 Today, large telescopes use charge-coupled devices
(CCDs) instead of photographic plates to record images.
These devices convert light signals into electric signals in
digital format.
 Then the images can be processed in many ways using
computer software.
Satellites
 Astronomers use artificial satellites, such as the Hubble
space telescope, to look into space.
 Some communications satellites are placed in low Earth
orbit, while others are placed in geosynchronous orbit.
 Low Earth orbit satellites are placed 200-800 km high
above the ground. They circle the Earth faster than the
Earth rotates.
 Geosynchronous orbit satellites move in the same
direction as Earth rotates. They are placed about 36,000
km above Earth, directly over the equator and appear
motionless. Radio and TV satellites are usually placed in
this type of orbit.
 Observation satellites are used for forecasting weather,
research, measure depth of snow, location of forest fires
etc.
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 The science of taking measurements of Earth (and other
planets) from space is known as remote sensing.
 Global Positioning System (GPS) uses a fleet of GPS
satellites above Earth and a small hand-held GPS unit on
Earth. It can calculate your position on Earth to within 30
m (military units can be accurate to within a few
centimeters).
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Lesson 5 – The Solar System Up Close
 Everything in the solar system is under the influence of
the Sun’s gravity. The Sun is made up of mostly hydrogen
and it is about 1.4 million km in diameter (110xEarth’s).
Moon and Planets
 The Moon is the first place (and only) on which man has
managed to land. On July 17, 1969 two Americans, Neil
Armstrong and Edwin Aldrin, were the first to make it to
the Moon.
 There are nine planets in our solar system and no two are
exactly the same. They differ in size, motion,
composition, density, and temperature. However, some
have few similar features.
 The inner planets – Mercury, Venus, Earth, and Mars –
are sometimes called the terrestrial planets, because of
their rocky composition. The outer planets – Jupiter,
Saturn, Uranus, and Neptune – are similar because of
their gaseous composition.
Exploring the Outer Space
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Two spacecrafts, Voyager 1 and Voyager 2, were designed by
NASA and sent to the edge of the solar system with
gravitational assists from the planets.
People in Space
 The Soviet Union was the first to successfully orbit a
satellite with no astronauts inside – Sputnik 1 (1957). On
April 12, 1961, Cosmonaut Yuri Gagarin, was the first
person in space aboard Vostok 1, which orbited the Earth
once at 302 km above the surface.
 The first American in space was Alan Shepard on May 5,
1961 (aboard Freedom 7). He flew a sub-orbital flight.
 A sub-orbital trajectory is one in which the spacecraft is
boosted above the atmosphere and then falls back to Earth
without going into orbit.
 In 1962, astronaut John Glenn was the first American to
make a full orbital flight.
The Apollo Program
 The Apollo Program was designed to send a three-person
team to the Moon, land two of them, and bring everyone
back safely.
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 The Apollo spacecraft consisted of an orbiter and a lander
(the lunar module). In the summer of 1969, Apollo 11
carried the first humans to the Moon. Neil Armstrong was
the first man to step onto the Moon’s surface, followed by
Edwin Aldrin. Michael Collins manned the command
module in lunar orbit.
 Eventual Soviet-American co-operation resulted in joint
missions – the Apollo/Soyuz test project was flown in 1975.
It was the first international space mission.
The Space Shuttle
 The first Shuttle, Columbia, flew its first mission in 1981.
Seven months later it flew again. The Canadian-built space
arm , Canadarm, was tested on this flight and has been part
of all shuttles since.
 Marc Garneau was the first Canadian aboard a space shuttle
in 1984 (Challenger). Roberta Bondar became the second in
1992 aboard the Discovery.
 In addition to launching and fixing satellites, the shuttles are
being used to help build the International Space Station
(ISS).
 Canada developed a second generation of space robotics for
the ISS, called the Canadian space station remote
manipulator system (SSRMS) or “Canadarm2” (giant
mechanical arm attached to the space station).
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 The ISS will provide laboratory for long-term research in
various fields (biology, chemistry, physics, medicine). This
research will be done in micro-gravity (zero gravity)
environment.
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