Transcript Section 2 Movements of the Earth

Chapter 26
Section 1 Viewing the Universe
Objectives
• Describe characteristics of the universe in terms
of time, distance, and organization
• Identify the visible and nonvisible parts of the
electromagnetic spectrum
• Compare refracting telescopes and reflecting
telescopes
• Explain how telescopes for nonvisible
electromagnetic radiation differ from light
telescopes
Chapter 26
Section 1 Viewing the Universe
The Value of Astronomy
astronomy the scientific study of the universe
• Scientists who study the universe are called
astronomers
• Astronomers have made exciting discoveries, such
as new planets, stars, black holes, and nebulas.
• By studying these objects, astronomers have been
able to learn more about the origin of Earth and
the processes involved in the formation of our
solar system.
Chapter 26
Section 1 Viewing the Universe
The Value of Astronomy,
• Studies of how stars shine may one day lead to
improved or new energy sources on Earth.
• Astronomers may also learn how to protect us
from potential catastrophes, such as collisions
between asteroids and Earth.
Chapter 26
Section 1 Viewing the Universe
Where does the Value of
Astronomy come into play?
• Astronomical research is supported by federal
agencies, such as the National Science Foundation
and NASA.
• Private foundations and industry also fund
research in astronomy.
• We can all gain from what they learn.
Chapter 26
Section 1 Viewing the Universe
Characteristics of the Universe
• The evolution of the universe is called
cosmology.
• Most astronomers believe the universe
began about 14 billion years ago.
• We study the stars to see the past and
predict the future.
Chapter 26
Section 1 Viewing the Universe
Organization of the Universe
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The solar system includes the sun, Earth, the
other planets, and many smaller objects such as
asteroids and comets.
The solar system is part of a galaxy.
– galaxy a collection of stars, dust, and gas bound
together by gravity
The galaxy in which the solar system resides is
called the Milky Way galaxy.
The nearest part of the universe to Earth is our
solar system.
A Galaxy
The Same Galaxy
Chapter 26
Section 1 Viewing the Universe
Measuring Distances
• What are some ways we measure distances?
Chapter 26
Section 1 Viewing the Universe
Measuring Distances in the Universe
• astronomical unit the average distance
between the Earth and the sun;
approximately 150 million kilometers
(symbol, AU)
• Astronomers also use the speed of light to
measure distance.
Chapter 26
Section 1 Viewing the Universe
Measuring Distances in the Universe
• Light travels at 300,000,000 m/s. In one
year, light travels 9.4607 x 1012 km. This
distance is known as a light-year.
• Aside from the sun, the closet star to Earth
is 4.2 light-years away.
Chapter 26
Section 1 Viewing the Universe
Observing Space
• What we see in the universe is light that was
formed a long time ago.
• It take light from the sun about 8 min. to
reach the earth.
Chapter 26
Section 1 Viewing the Universe
Electromagnetic Spectrum
• electromagnetic spectrum all of the frequencies
or wavelengths of electromagnetic radiation.
• Light, radio waves, and X rays are all examples of
electromagnetic radiation.
• The radiation is composed of traveling waves of
electric and magnetic fields that oscillate at fixed
frequencies and wavelengths.
Chapter 26
Section 1 Viewing the Universe
Visible Electromagnetic Radiation
• Though all light travels at the same speed,
different colors of light have different
wavelengths. These colors can be seen when
visible light is passed through a spectrum.
• The human eye can see only radiation of
wavelengths in the visible light range of the
spectrum.
Chapter 26
Section 1 Viewing the Universe
Visible Electromagnetic Radiation
• Electromagnetic radiation shorter or longer than
wavelengths of violet or red light cannot be seen
by humans.
• The shortest visible wavelength of light are blue
and violet, while the longest visible wavelength of
light are orange and red.
The Electromagnetic Spectrum
Section 1 Viewing the Universe
Reading check
Which type of electromagnetic radiation can
be seen by humans?
Chapter 26
Section 1 Viewing the Universe
Reading check
Which type of electromagnetic radiation can
be seen by humans?
The only kind of electromagnetic radiation the
human eye can detect is visible light.
Chapter 26
Section 1 Viewing the Universe
Invisible Electromagnetic Radiation
• Invisible wavelengths include infrared waves,
microwaves, radio waves, ultraviolet rays, X rays,
and gamma rays, and are detected only by
instruments.
• In 1852, a scientist named Sir Frederick William
Herschel discovered infrared, which means
“below the red.”Infrared is radiation that has
waves longer than waves of visible light.
• Ultraviolet means “beyond the violet” and has
wavelengths shorter than waves of visible light.
Chapter 26
Section 1 Viewing the Universe
Telescopes
• telescope an instrument that collects
electromagnetic radiation from the sky and
concentrates it for better observation.
• In 1609, an Italian scientist, Galileo, heard of a
device that used two lenses to make distant objects
appear closer.
• Telescopes that collect only visible light are called
optical telescopes.
Chapter 26
Section 1 Viewing the Universe
Telescopes
• The two types of optical telescopes are
refracting telescopes and reflecting
telescopes.
Optical Telescopes
• Refractors
–Focus light with refraction:
bend light path in transparent medium
–Use lenses
–First kind made
–Kind used by Galileo
• Reflectors
–Focus light by reflection:
bounce light off a solid medium
–Use mirrors
–First designed and created by Sir Isaac Newton
–Many different designs
Chapter 26
Section 1 Viewing the Universe
Refracting Telescopes
• refracting telescope a telescope that uses a set of
lenses to gather and focus light from distant
objects
• The bending of light is called refraction.
• Refracting telescopes have an objective lens that
bends light that passes through the lens and
focuses the light to be magnified by an eyepiece.
Chapter 26
Section 1 Viewing the Universe
Refracting Telescopes
First Optical Telescopes:
Refractors
Image of source is formed on focal
plane and magnified by eyepiece.
Chapter 26
Section 1 Viewing the Universe
Refracting Telescopes
• One problem with refracting telescopes is that the
lens focuses different colors of light at different
distances causing the image to distort.
• Another problem is that objective lenses that are
too large will sag under their own weight and
cause images to become distorted.
Chromatic Aberration
• Dispersion of light through optical material causes blue
component of light passing through lens to be focused
slightly closer to lens than red component.
• Known as chromatic aberration.
Chapter 26
Section 1 Viewing the Universe
Reflecting Telescopes
• In the mid-1600s Isaac Newton solved the
problem of color separation that resulted from the
use of lenses.
• reflecting telescopes a telescope that uses a
curved mirror to gather and focus light from
distant objects
Chapter 26
Section 1 Viewing the Universe
Reflecting Telescopes
Reflecting Telescopes
Chapter 26
Section 1 Viewing the Universe
Reflecting Telescopes
• When light enters a reflecting telescope, the light
is reflected by a large curved mirror to a second
mirror. The second mirror reflects the light to the
eyepiece, where the image is magnified and
focused.
• Unlike refracting telescopes, reflecting telescopes
can be made very large without affecting the
quality of the image.
Chapter 26
Section 1 Viewing the Universe
Reading check
What are the problems with refracting
telescopes?
Chapter 26
Section 1 Viewing the Universe
Reading check, continued
What are the problems with refracting telescopes?
Images produced by refracting telescopes are
subject to distortion because of the way different
colors of visible light are focused at different
distances from the lens and because of weight
limitations on the objective lens.
Chapter 26
Maps in Action
Maps in Action
Light Sources
Chapter 26
Section 1 Viewing the Universe
Telescopes for Invisible
Electromagnetic Radiation
• Scientists have developed telescopes that
detect invisible radiation, such as a
radiotelescope for radio waves.
• Ground-based telescopes work best at high
elevations, where the air is dry.
Chapter 26
Section 1 Viewing the Universe
Telescopes for Invisible
Electromagnetic Radiation
• The only way to study many forms of
radiation is from space because the Earth’s
atmosphere acts as a shield against many
forms of electromagnetic radiation.
Chapter 26
Section 1 Viewing the Universe
Space-Based Astronomy
• Space telescopes have been launched to
investigate planets, stars, and other distant
objects
• In space, Earth’s atmosphere cannot
interfere with the detection of
electromagnetic radiation.
Chapter 26
Section 1 Viewing the Universe
Reading check
Why do scientists launch spacecraft beyond
Earth’s atmosphere?
Chapter 26
Section 1 Viewing the Universe
Reading check, continued
Why do scientists launch spacecraft beyond
Earth’s atmosphere?
Scientists launch spacecraft into orbit to detect
radiation screened out by Earth’s atmosphere and
to avoid light pollution and other atmospheric
distortions.
Chapter 26
Section 1 Viewing the Universe
Space-Based Astronomy
• A space telescope does not have to view the
stars through the earths atmosphere.
• The same telescope in space will see many
times further than on earth.
Chapter 26
Section 1 Viewing the Universe
Space Telescopes
• The Hubble Space Telescope collects
electromagnetic radiation from objects in space.
• The Chandra X-ray Observatory makes
remarkably clear images using X rays from
objects in space, such as remnants of exploded
stars.
• The Compton Gamma Ray Observatory detected
gamma rays from objects, such as black holes.
• The James Webb Space Telescope will detect
infrared radiation from objects in space after it is
launched in 2011.
Hubble Space Telescope
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Launched from the Space Shuttle in 1990.
Largest telescope in space: 2.4 meter mirror.
Mirror has an optical flaw (spherical aberration).
Hubble was fixed by astronauts in 1994.
Hubble has higher resolution and gathers more
light than most Earth-based telescopes.
Our Sun in Different Wavelengths
X-Ray (Yohkoh)
Ultraviolet (SOHO)
Infrared (NSO)
Visible (BBSO)
Radio (Nobeyama)
Crab Nebula at Different Wavelengths
x-ray
far UV
visible
infrared
near UV
radio
Chapter 26
Section 1 Viewing the Universe
Other Spacecraft
• Since the early 1960s, spacecraft have been sent out of
Earth’s orbit to study other planets.
• The Voyager 1 and Voyager 2 spacecraft investigated
Jupiter, Saturn, Uranus, and Neptune, and collected images
of these planets and their moons.
• The Galileo spacecraft orbited Jupiter and its moons from
1995 to 2003.
• The Cassini-Huygens spacecraft will study Titan, Saturn’s
largest moon. Like Earth, Titan has an atmosphere that is
rich in nitrogen. Scientists hope to learn more about the
origins of Earth by studying Titan.
Chapter 26
Section 1 Viewing the Universe
Human Space Exploration
• Spacecraft that carry only instruments and computers are
described as robotic and can travel beyond the solar
system.
• The first humans went into space in the 1960’s. Between
1969 and 1972, NASA landed 12 people on the moon.
Humans have never gone beyond Earth’s moon.
• The loss of two space shuttles and their crews, the
Challenger in 1986 and the Columbia in 2003, have
focused public attention on the risks of human space
exploration.
Chapter 26
Section 1 Viewing the Universe
Spinoffs of the Space Program
• Satellites in orbit provide information about
weather all over Earth.
• Other satellites broadcast television signals from
around the world or allow people to navigate cars
and airplanes.
• Even medical equipment, like the heart pump,
have been improved based on NASA’s research on
the flow of fluids through rockets.
Chapter 26
Section 2 Movements of the Earth
Objectives
• Describe two lines of evidence for Earth’s rotation.
• Explain how the change in apparent positions of
constellations provides evidence of Earth’s rotation and
revolution around the sun.
• Summarize how Earth’s rotation and revolution provide a
basis for measuring time.
• Explain how the tilt of Earth’s axis and Earth’s movement
cause seasons.
Chapter 26
Section 2 Movements of the Earth
The Rotating Earth
rotation the spin of a body on its axis
• Each complete rotation takes about one day.
• The Earth rotates from west to east. At any given moment,
the hemisphere of Earth that faces the sun experiences
daylight. At the same time, the hemisphere of Earth that
faces away from the sun experiences nighttime.
• These movements of Earth are also responsible for the
seasons and changes in weather.
Chapter 26
Section 2 Movements of the Earth
The Foucault Pendulum
• In the 19th century, the scientist JeanBernard-Leon Foucault, provided evidence
of Earth’s rotation by using a pendulum.
• The path of the pendulum appeared to
change over time. However, the path does
not actually change. Instead, the Earth
moves the floor as Earth rotates on its axis.
Chapter 26
Section 2 Movements of the Earth
The Coriollis Effect
• The rotation of Earth causes ocean currents
and wind belts to curve to the left or right.
• This curving is caused by Earth’s rotation
and is called the Coriolis effect.
Chapter 26
Section 2 Movements of the Earth
The Revolving Earth
• The Earth is traveling around the sun at an
average speed of 29.8 km/s.
• One complete trip along an orbit is called
revolution.
• Each complete revolution of Earth around
the sun takes 365 1/4 days, or about one
year.
Chapter 26
Section 2 Movements of the Earth
Earths Orbit
• Earth’s orbit around the sun is an ellipse.
• An ellipse is a closed curve whose shape is
determined by two points, or foci, within
the ellipse.
• Earth is not always the same distance from
the sun.
• perihelion the point in the orbit of a planet
at which the planet is closet to the sun
• aphelion the point in the orbit of a planet at
which the planet is farthest from the sun
Chapter 26
Section 2 Movements of the Earth
Evidence of Earth’s Rotation
• A constellation is a group of stars that are
organized in a recognizable pattern.
• Constellations appear to change positions in
the sky.
• The rotation of Earth on its axis causes the
change in position.
Chapter 26
Section 2 Movements of the Earth
Evidence of Earth’s Revolution
• Earth’s revolution around the sun is
evidenced by the apparent motion of
constellations.
• Thus different constellations will appear in
the night sky as the seasons change.
Chapter 26
Section 2 Movements of the Earth
Constellations and Earth’s Motion
Chapter 26
Section 2 Movements of the Earth
Spot Question
How does movement of constellations provide
evidence of Earth’s rotation and revolution?
Chapter 26
Section 2 Movements of the Earth
Spot Question
How does movement of constellations provide
evidence of Earth’s rotation and revolution?
Constellations provide two kinds of evidence of Earth’s
motion. As Earth rotates, the stars appear to change
position during the night. As Earth revolves around the
sun, Earth’s night sky faces a different part of the universe.
As a result, different constellations appear in the night sky
as the seasons change.
Chapter 26
Section 2 Movements of the Earth
Measuring Time
• Earth’s motion provides the basis for measuring time.
• A day is determined by Earth’s rotation on its axis. Each
complete rotation of Earth on its axis takes one day, which
is then broken into 24 hours.
• The year is determined by Earth’s revolution around the
sun. Each complete revolution of Earth around the sun
takes 365 1/4 days, or one year.
Chapter 26
Section 2 Movements of the Earth
Formation of the Calendar
• A calendar is a system created for
measuring long intervals of time by
dividing time into periods of days, weeks,
months, and years.
• A year is 365 1/4 days long.
• Every four years, one day is added to the
month of February.
• Any year that contains an extra day is called
a leap year.
Chapter 26
Section 2 Movements of the Earth
The Modern Calendar
• In the late 1500s, Pope Gregory XIII
created a calendar that would stay aligned
with the seasons.
• In this Gregorian calendar, century years,
such as 1800 and 1900, are not leap years
unless the century years are exactly
divisible by 400.
Chapter 26
Section 2 Movements of the Earth
Time Zone
• The earth rotates about 15o every hour.
• Earth’s surface has been divided into 24
standard time zones.
• Each time zone is about 15o.
• The time zone is one hour earlier than the
time in the zone east of each zone.
Chapter 26
Section 2 Movements of the Earth
International Date Line
• The International Date Line was established
to prevent confusion about the point on
Earth’s surface where the date changes.
• This line runs from north to south through
the Pacific Ocean. The line is drawn so that
it does not cut through islands or continents.
Chapter 26
Section 2 Movements of the
Earth
Spot Question
• What is the purpose of the International Date Line?
• It is a time zone border, the calendar moves ahead one
day as you cross it. The purpose of the International
Date Line is to locate the border so that the transition
would affect the least number of people. So that it will
affect the least number of people, the International Date
Line is in the middle of the Pacific Ocean, instead of on
a continent.
Chapter 26
Section 2 Movements of the Earth
Measuring Time
Chapter 26
Section 2 Movements of the
Earth
Daylight Savings Time
• Because of the tilt of Earth’s axis, daylight time is
shorter in the winter months than in the summer
months.
• During the summer months, days are longer so
that the sun rises earlier in the morning.
• daylight savings time
– Under this system, clocks are set one hour
ahead of standard time in April, and in October,
clocks are set back one hour to return to
standard time.
Why is it hot in the tropics?
Why is it cold at the poles?
The seasons are caused by:
• Changes in the angle at which the sun’s rays strike
Earth’s surface.
• unequal heating
• rotation of the earth on its axis
• revolution of the earth around the sun
• 23.5O tilt of the earth axis from perpendicular to
the plane of the ecliptic
• time exposure
Chapter 26
Section 2 Movements of the Earth
Equinoxes
• equinox the moment when the sun appears
to cross the celestial equator
• At an equinox, the sun’s rays strike Earth at
a 90° angle along the equator.
• The hours of daylight and darkness are
approximately equal everywhere on Earth
on that day. (12 hours)
EQUINOXES
VERNAL(spring), MARCH 21
AUTUMNAL(Fall), SEPTEMBER 21
Chapter 26
Section 2 Movements of the Earth
Summer Solstices
• solstice the point at which the sun is as far north
or as far south of the equator as possible
• The sun’s rays strike the Earth at a 90° angle along
the Tropic of Cancer.
• The summer solstice occurs on June 21 or 22 of
each year and marks the beginning of summer in
the Northern Hemisphere.
• The farther north of the equator you are, the longer
the period of daylight you have.
Chapter 26
Section 2 Movements of the Earth
Winter Solstices
• The sun’s rays strike the Earth at a 90° angle along
the Tropic of Tropic of Capricorn.
• The winter solstice occurs on December 21 or 22
of each year and marks the beginning of winter in
the Northern Hemisphere.
• Places that are north of the Arctic Circle then have
24 hours of darkness.
• Places that are south of the Antarctic Circle have
24 hours of daylight at that time.
SOLSTICES
SUMMER, JUNE 21
WINTER, DECEMBER 21
Where are the
overhead rays of the
sun on these days?
Which parts of the
earth are in darkness
and light? For how
long?
Chapter 26
Section 2 Movements of the Earth
The Seasons
• The earth is tilted 23.5º from perpendicular to the
plane of the ecliptic.
Notice these four
important parallels.
Where do they
occur? Why?
Tropic of Cancer at 23.5º N
Tropic of Capricorn at 23.5º S
Arctic Circle (66.5 º N)
Antarctic Circle (66.5º S)
Effects of the Seasons
Changes in solar intensity
• Changes in solar altitude
• Changes in day length
• Changes in temperature
All of these changes are most extreme at high
latitudes and minimized at the equator.
We will talk more about this in chapter 22.