Objectives

Section 1 Viewing the UniverseChapter 26Objectives

• 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

Section 1 Viewing the Universe

The Value of Astronomyastronomy 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 UniverseChapter 26

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.

Section 1 Viewing the UniverseChapter 26Where 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.


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.


Organization of the Universe• 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


Measuring Distances

• What are some ways we measure distances?


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.


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.


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.


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.

Section 1 Viewing the UniverseChapter 26Visible 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.

Section 1 Viewing the UniverseChapter 26Visible 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?


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.


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.

Section 1 Viewing the UniverseChapter 26Telescopes

• 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.

Section 1 Viewing the UniverseChapter 26Telescopes

• 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

Section 1 Viewing the UniverseChapter 26Refracting 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.


First Optical Telescopes:Refractors

Image of source is formed on focal plane and magnified by eyepiece.


• 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.


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





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.


Reading check

What are the problems with refracting telescopes?


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.

Maps in ActionChapter 26

Maps in ActionLight Sources

Section 1 Viewing the UniverseChapter 26Telescopes 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.

Section 1 Viewing the UniverseChapter 26Telescopes 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.

Section 1 Viewing the UniverseChapter 26Space-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.


Reading check

Why do scientists launch spacecraft beyond Earth’s atmosphere?


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.


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.


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

• 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) Visible (BBSO)

Infrared (NSO) Radio (Nobeyama)

Crab Nebula at Different Wavelengths

x-ray far UV near UV

visible infrared radio


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.


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.


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.

Section 2 Movements of the EarthChapter 26

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

The Rotating Earthrotation 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.

Section 2 Movements of the Earth

Chapter 26

The Foucault Pendulum• In the 19th century, the scientist Jean-

Bernard-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

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 26The 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 26Earths 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

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

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

Constellations and Earth’s Motion


Chapter 26

Spot Question

How does movement of constellations provide evidence of Earth’s rotation and revolution?


Chapter 26

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 26Measuring 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

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

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

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

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

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

Measuring Time


Chapter 26

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

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)


EQUINOXESVERNAL(spring), MARCH 21AUTUMNAL(Fall), SEPTEMBER 21

Chapter 26

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

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.


SOLSTICESSUMMER, JUNE 21WINTER, 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

The Seasons• The earth is tilted 23.5º from perpendicular to the

plane of the ecliptic.


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)

Notice these four important parallels.Where do they occur? Why?

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.

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Objectives