11 our understanding of the universe

372 UNIT D

What you will learn:• First Nations and Métis understandings describe and explain some

astronomical phenomena including the origin of the universe.

• Astronomy is making sense of the universe that lies beyond Earth, bothfrom holistic and cultural viewpoints and from scientific viewpoints.

• Astronomical bodies have unique characteristics and composition, whichmay affect how they interact with one another.

• Improved technology and observation has lead to the development of differenttheories on how the universe and our solar system may have formed.

• Ongoing space research continues to be important.

The Hubble telescope found this very young, still-forming galaxy, almost 12.8 billion light-years fromEarth. Astronomers believe it started to form just 700 million years after the Big Bang occurred.

Monitoring Understanding

Good readers keep track of places where their understanding of new wordsor ideas breaks down, and they use strategies to improve their understanding.Preview the Key Terms and the subheadings for section 11.1. Makepredictions about places where you may have difficulty understanding the ideas.

Before Reading

Our understanding of the universe is culturally influenced.

By the end of this chapter,you will:

• examine how variouscultures, past and present,including First Nations and Métis, understand andrepresent astronomicalphenomena

• inquire into the motion and characteristics ofastronomical bodies in our solar system and the universe

• analyze scientificexplanations of theformation and evolution of our solar system and the universe

Key Terms• apparent retrograde motion• Big Bang theory• electromagnetic radiation• electromagnetic spectrum• geocentric models• heliocentric model • orbital radius • red-shifted• spectral lines • spectralshifting • spectroscope • spectrum

Outcomes

11

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Explanations for the Origins of the UniverseAncient cultures used their observations and traditionalunderstanding to explain the world around them, including how the universe was created.

In Chinese culture, for example, believed that the universebegan as a big, black egg. Inside the egg was Pan Gu, who was the first living being and creator (Figure 11.1). When he crackedopen the egg, the clear part of the egg floated up and became theheavens, and the rest of the egg became Earth. When Pan Gu diedmany, many years later, his eyes became the Sun and the Moonand his hair and beard became the stars in the sky.

The understanding of the Cree people in Saskatchewanattribute the creation of the universe, Sun, other stars, and Earthto Creator. Some creation stories do not necessarily describe thecreation of the universe, but they detail a great flood event priorto the creation of humans. Cherokee Thomas King, in his bookGreen Grass, Running Water, notes, “In the beginning, there was nothing. Just the water.”

Here is a summary of what youwill learn in this section:

• Astronomy differs amongcultures. For instance,scientific astronomy is figuringout from observations how the physical universe works.Indigenous astronomy is comingto know what is beyond MotherEarth and involves makingsense of the universe in acultural context.

• Throughout history, humans inmany different cultures aroundthe world, including FirstNations and Métis, haveexplained the universe basedon their worldview, what theybelieve, and what they are able to observe.

Cultural Explanations

Figure 11.1 The giant Pan Gu holds the egg of the universe, which is often shown as the yin and yang symbol. According to Chinese ideas, when the egg was cracked open, theuniverse was created.

11.1

37311.1 Cultural Explanations©P


374 UNIT D Exploring Our Universe©P

D19 Quick Science

There are many different cultural understandingsfrom all over the world about how the universe wascreated. Researching ideas unfamiliar to us helps us learn more about the universe.

PurposeTo explore creation stories from different cultures

Procedure1. Research a creation story from a culture of

your choice. Cultures may include• Africa: Maasai, Zulu• Asia: Hindu, Japanese, Korean, Mongol• Central and North America: Aztec, Cree,

Dené, Lakota, Mayan, Navajo• Middle East: Babylonian, Jewish/Christian,

Persian• Pacific: Australian Aborigine, Hawaiian, Maori• South America: Incan

2. Often, cultural understandings are part of an oraltradition. In keeping with that tradition, assumethe role of a storyteller and share your story.

Questions3. After listening to the different stories, write a one-page

mini-essay that answers the following questions:

Creation of the Universe(a) What are the similarities between stories?

Why might these similarities exist?

(b) What do the stories tell you about the culture they are from?

(c) What may have influenced the creation ofthese stories? These influences may includethe environment, politics, technology, and society.

(d) How might these stories influence theeveryday lives of the people in the respective cultures?

Pose More Questions4. As you have learned, oral storytelling is a common

way different cultures tell their creation stories,but there are many other ways to express or tellthose same stories. What ways can you think of that a culture might use? Give an example in your answer.

5. What questions do you have about the origin of the universe that were not answered by thecreation story you researched?

Suggested Activity •D20 Quick Science on page 377

Other Ways of Knowing the UniverseSimilar to the Cree, the Dené of northern Saskatchewan believethat Creator made the universe and everything in it. Theirspiritual accounts, called U"æqhzé, explain their place within the universe and creation.

In Saskatchewan, First Nations and Métis peoples have richcreation stories, which explain their people’s origin and theirplace in the universe. Nakawe– people, who are descendants of the Anishinabe from Ontario who migrated west long ago, havesimilar stories. Elder Danny Musqua, a Nakawe– Elder, recountsthe shared creation story of the Anishinabe and Nakawe– peoples.Creator is both mother and father. Elder Danny’s people understandthat the physical universe came from the woman spirit, which in turn came from Creator. The universe, explains Elder Danny,is the physical expression of the Mother’s spirit.

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Improving UnderstandingUsing Images

Make a note of the sentencesor paragraphs that you do not understand. Look at thefigures on that page and thepages before and after it.Reread each sentence orparagraph, and connect thewords and ideas to the images.How do the images help youto understand the words?

During Reading

It is the woman spirit that gave life to all four corners of theuniverse and then, in turn, created Earth. Thus, the Nakawe– callour planet Mother Earth. People originate as spirits who residewith Creator, but then are transformed into physical bodies inorder to understand what it means to be made physical. Peoplelive in the physical world to learn about it until they find theirway back to the spirit world.

According to Albert Scott, a traditional Knowledge Keeperfrom the Kinistin Saulteaux First Nation, there are four levelsabove Earth. The first level has the stars and the sky we can see.Long ago, Creator’s helpers looked down from the fourth level.They saw only disorganization. One of the helpers said, “Watchme,” and created the sky and what scientists call the universe.

The ancient Egyptians believed that in the beginning, therewas a chaotic and endless ocean called Nu. From this chaos,Amen-Renef, or “He Whose Real Essence Is Unknown,” createdhimself. Once created, he was known as Atum. He created the air god, Shu, and the water goddess, Tefnut. Shu and Tefnut had twins: Nut, who represents the sky, and Geb, who is Earth.The importance of Nut and Geb can be seen in the paintingsinside of tombs that show both the heavens and Earth (Figure 11.2).

The Egyptians believed that the goddess Nut’s body was thesky. Her body acted as a shield against the chaos that lay beyondher, beyond what the ancient Egyptians could see. Nut protectedthe ordered cosmos of this world. Every evening, as the Sun set, theSun god Ra entered her mouth only to be reborn the next morningat sunrise. The Sun and the god Ra were very important to theEgyptians. They believed the Sun was the centre of the universe.

37511.1 Cultural Explanations©P

Figure 11.2 The goddess Nut coversEarth and protects all its inhabitants.Her fingers and toes touch the fourdirections. The Egyptians believedthat stars, which cover her body, come from Nut.


Like the Egyptians, the Boshongo people in the Congoalso believed that in the beginning, there was a singleentity who existed in a dark, watery place. According tothe Boshongo, the god Bumba was surrounded by nothingbut water and darkness. One day, Bumba had pains in his stomach. The pains became worse and worse. Hevomited up the Sun, and there was suddenly light allaround (Figure 11.3). The heat from the Sun made thewater evaporate, creating the clouds and causing the waterto recede and show the edges of the world. He vomitedagain, this time producing the Moon and the stars thatgive light at night. He was still in pain, and this time hevomited nine creatures: the leopard, the crested eagle, the crocodile, a little fish, the tortoise, lightning, the white heron, a beetle, a goat, and humans. From thesecreatures, all the other creatures came into existence.

Culture has not only influenced the creation of stories,it has also influenced the development of Eurocentricscience. In the next section, you will learn about specificscientific theories.Figure 11.3 According to Boshongo stories,

the god Bumba created Earth and the heavens,and humans by vomiting.


1. (a) Using a Venn diagram, identifysimilarities and differences among the creation stories you studied in this section.

(b) Why do you think that there aresimilarities and differences among thecreation stories of different cultures?

2. Think about the environment that you livein. Create a story about the creation of theuniverse based upon the observations youmake about where you live.

3. How is the Egyptian creation storyreflective of their belief in reincarnation?

4. Why do you think humans, regardless ofculture, have attempted to explain theorigin of the universe?

CHECK and REFLECT11.1

5. In the shared creation story of theAnishinabe and Nakawe– peoples, ElderDanny explains that the physical universecomes from the woman spirit. How is thisunderstanding reflected in the way theAnishinabe and Nakawe– peoples refer to planet Earth?

6. The Cree, Egyptian, and Boshongo creationstories share the element of water. Whatother creation stories do you know thatinvolve a beginning with water? What mightbe some explanations for these similarities?

7. What creation story did you find the mostsurprising? Explain why.

(a)

(b)


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D20 Quick Science

In the past and still today, different cultures usedifferent methods to explain the universe andhumanity’s role in it. The study of the universe and our role in it is called cosmology.

Scientists publish scientific papers with theirexplanations of cosmology, and other cultures use artforms, such as dance, songs, paintings, or architecture.For example, the Cheyenne used symbols and coloursto represent the creation of the universe and theCheyenne role within that universe (Figure 11.4).

Cosmology and Art

Questions3. Why do you think there are so many examples

of cosmology in art?

4. How are the art forms influenced by the naturalworld?

5. Why do you think art has been used to conveyknowledge?

6. What modern examples of how cosmologyinfluences art are present in Canadian society?

7. Are there other ways, other than art and scientificpapers, in which our beliefs or knowledge abouthow the universe has been created have beenexpressed? Explain your answer.

Pose New Questions8. What questions do you have about the origin

of the universe that are not answered by your findings?

9. Choose a classmate’s presentation. Whatquestions do you have about the culture’s beliefs that he or she presented?

Figure 11.4 Artist Mike Schwab painted this bag with symbolsthat derive from traditional Cheyenne cosmological symbols.The design has a personal, private meaning for the artist.

Key ActivityDI

Procedure1. Using the library or the Internet, research

different ways that cultures used art to representtheir knowledge of cosmology.

2. From your research, present examples of howcultures have combined cosmology and art. Present your finding, or create an example of thetype of art used by a culture. Be sure to explainthe link between the cosmology and the art form.


Explaining the Origin of the UniverseEdwin Hubble was an American astronomer who was one of thefirst scientists to study galaxies (Figures 11.5 and 11.6). Between1918 and 1929, two of his major findings changed astronomy.First, he confirmed that many other galaxies existed beyond theMilky Way. Second, he found that almost all galaxies are moving awayfrom each other. These observations helped to support the proposalmade in 1927 by Belgian priest and physicist Georges Lemaître that theuniverse is expanding. Both of these ideas would lead astronomers andphysicists to develop theories on how the universe may have formed.

More people recognize Hubble’s contribution because he hadevidence to support his ideas. The evidence Hubble used to reachhis conclusions came from measuring the distance from Earth of46 galaxies and the speed of their movement. Hubble closelyexamined each galaxy’s light spectrum. When white light passesthrough a prism, it is separated into a continuous rainbow knownas the visible light spectrum. In science, a spectrum refers to theseparation of radiation, such as light, into different wavelengths.This is pluralized as spectra, or sometimes as spectrums.

The measurements of different light spectra helped supportHubble’s theory. Evidence from thousands of observations ofgalaxies has confirmed his findings. Hubble’s work remains thefoundation of modern understanding of the nature and origin of the universe.

378 UNIT D Exploring Our Universe

Here is a summary of what youwill learn in this section:

• The Big Bang theory of theformation and expansion of the universe is consistent withknown laws of the universe.

• The red shift of spectral lines in the light we see from galaxiesshows that the light’s wavelengthsare getting longer, meaningthat other galaxies are movingaway from us.

• The cosmic backgroundradiation in the universe, now mapped, is thought to beleftover energy from the momentthe universe first formed.

• Today, scientists’understandings are basedupon a heliocentric, or Sun-centred, model.

Scientific Theories

Figure 11.5 The Hubble Space Telescope was named for astronomer Edwin Hubble.

11.2

Figure 11.6 American astronomerEdwin Hubble (1889–1953) using the 100-inch (250-cm) telescope at the Mount Wilson Observatory, Los Angeles, California, in 1937

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37911.2 Scientific Theories©P

D21 Quick Science

A device called a spectroscope enables us to split alight sample into its component colours, or spectra.Each element produces its own unique lightspectrum. By studying light spectra, scientists candetermine the composition of different astronomicalbodies, even if those sources are extremely far away.

PurposeTo build a spectroscope to observe and compare thespectra of different light sources

Using a Spectroscope

3. Place the CD into the opening you made in step 2.Use your protractor to be sure that the CD isplaced on an angle of 60 degrees.

4. Tape the bottom of the CD to the box.

5. You may wish to use duct tape to cover part of the eyepiece for better viewing.

6. Using your spectroscope, observe the CFL.Record the order of the colours and any blacklines that appear.

7. Repeat step 6 using different light sources.

Questions8. Pure white light produces a spectrum that is

a continuous rainbow. How is it different from the spectra produced by other light sources?

9. What differences did you notice among thespectra produced by different light sources?

10. (a) Which kind of light source produced themost distinct spectrum?

(b) Explain why you think that was the case.

11. If you used element spectrum tubes, how didthe spectra produced by the tubes differ fromthe spectra produced by the light sources?

12. The spectra produced by different light sourcesare like fingerprints. The pattern of lines can be used to identify if certain elements arepresent. How could knowledge of the spectra of light created by particular elements help an astronomer determine the composition of a distant star or galaxy?

Pose New Questions13. What other uses could you use a spectroscope

for? What do you think you could learn fromusing it?

Procedure1. Use the utility knife to carefully cut a slit on

one side of the box.

2. On the opposite side of the box, carefully cut an opening large enough to hold the CD. This is your viewing area (Figure 11.7).

• utility knife

• cardboard box

• CD or DVD

• protractor

• tape

• duct tape (optional)

• various light sources:compact fluorescentlamps (CFLs),incandescent bulbs,“black light” tubes,spectrum tubes fordifferent elements

• coloured pencils ormarkers

Materials & Equipment

Figure 11.7 Diagram of CD spectroscope

lightsource

CD/DVD

60°

slit

eye


Geneva

CERN research offices

largecollidingringaccess tunnels

smallcollidingring

particledetectors

Georges Lemaître

Georges Lemaître’s(1894–1966) idea that theformation of the universe wasjust “the Cosmic Egg explodingat the moment of the creation”would later become the BigBang theory. In 1933, Einsteinheard Lemaître explain histheory in detail. He acceptedthe theory, saying, “This is themost beautiful and satisfactoryexplanation of creation towhich I have ever listened.”

infoBIT Evidence for the Big Bang TheoryFrom the light spectrum of each galaxy he studied, Hubble wasable to determine the speed at which each galaxy was movingaway from our own. Then, for those same galaxies, he separatelydetermined the distance between each one and the Milky Way.Plotting both the speed and the distance measurements together,Hubble discovered a clear relationship between the two. Thefarther away a galaxy was, the faster it was moving away.

These findings, along with observations of many otherscientists of the time, gave further support to Lemaître’s idea that the universe is expanding. Out of this and the work of manyother physicists, mathematicians, and other scientists of the day,came one of the most remarkable theories of the 20th century.The theory, which came to be called the Big Bang theory, statesthat the universe formed when an infinitely dense point suddenlyand rapidly expanded in a single moment. All the matter andenergy that exists today was created during the early minutes of that hot, rapid expansion. Most of the credit for the Big Bangtheory goes to Russian-American physicist George Gamow andAmerican mathematician Ralph Alpher.

It is now commonly accepted by scientists that the universeformed 13.7 billion years ago. That moment marks the beginningof the universe and also the beginning of time. Today, at severalresearch facilities around the world, scientists are trying torecreate various aspects of the conditions that might have existedin the early moments of the universe (Figure 11.8). In this way,they hope to gain a better understanding of the origin ofeverything within the universe.


In 2008, there was a lot in the news about CERN and itsLarge Hadron Collider. Therewas much debate about itsuse. Research the controversyin the library or on the Internet.Once you have all yourinformation, express youropinion in an editorial. Be sure to support your opinionwith fact.

reSearch

Figure 11.8 At CERN in Switzerland, scientists are trying to break down particles of matter inside a27-km-long “supercollider” (shown here in blue), located deep in the ground. These experimentsmay reveal how the smallest particles of matter were created when the universe first formed.

Suggested Activity •D22 Quick Science on page 391


An Ever-Faster Expanding UniverseScientists compare the expansion of space to the expandingsurface of a balloon as it is inflating. Just as dots drawn on aballoon separate from each other as the balloon expands, soclusters of galaxies are moving away from each other as spaceopens up between them.

The effects of the expansion of space are so small that our MilkyWay galaxy is not moving away noticeably from our nearest galaxyneighbour, Andromeda. Gravity and other forces are strong enoughto keep these objects together. However, between clusters ofgalaxies is an immense amount of empty space. This is where the tiny effects of the expansion of space add up.

In the last 20 years, data from the most distant galaxies showthat the rate at which the most distant galaxies are receding fromour view is increasing. In other words, not only are galaxiesmoving away from us, but they are doing so at an ever-faster rate (Figure 11.9).


Figure 11.9 This spiral galaxy is NGC 4526; the small, bright spot is Supernova 1994D.

Learning Checkpoint

1. What is a light spectrum?

2. What two findings of Edwin Hubble changed astronomy?

3. What does the Big Bang theory explain?


Improving UnderstandingUsing Key Terms

As you read, identify the KeyTerms and write them in yournotebook. Look at the KeyTerms, and try to restate whatyou read using the words ascues. Talk with a partner tocompare what each of youunderstood from what you read.

During Reading

The Wave Nature of LightHow can a light spectrum tell us whether a galaxy is moving awayfrom us? First, we need to understand the nature of light. Light is aform of energy. Scientists have two ways of explaining how lighttravels: in waves or as energy parcels called photons. The waveform of energy is called electromagnetic radiation.

Figure 11.10 shows the full known electromagnetic spectrum,from radio waves with very long wavelengths, to gamma rayswith very short wavelengths. Humans can only see a smallfraction of the electromagnetic spectrum, a rainbow of coloursknown as the visible light spectrum. Each of the different coloursof the visible light spectrum, from red through to yellow and greenand on to violet, varies in wavelength. The wavelength of redlight, for example, is longer than the wavelength for blue light.Technology enables us to detect other forms of electromagneticradiation that are not readily visible to humans.


Analyzing the Movement of Light WavesTo understand the movement of light waves in space, considerwaves in a lake. Light waves move in a similar way to the waveson the surface of water. Picture a duck floating on a calm lake.

crest

Wavelength (μm) Wavelength (μm)

108 107 106 105 104 103 102 10 1 10�1 10�2 10�3 10�4 10�5 10�6 10�7

radio microwave infrared visible ultraviolet X-ray gamma rays

Figure 11.10 The electromagnetic spectrum. Objects in space emit a great variety of electromagnetic energy.


Gentle movements of the duck create ripples on the water surfacethat spread out evenly all around the duck (Figure 11.11(a)) in acircular pattern. The wavelength of these ripples is measured asthe distance from the crest of one wave to the crest of the next.

As the duck moves, the ripples in front of it compress and thewavelength shortens. At the same time, the ripples behind the duckstretch out and the wavelength gets longer (Figure 11.11(b)) in amore elliptical pattern. Even if you could not see the duck directlyand could only see the ripples on the water, you would still be ableto tell whether the duck was moving toward you or away from you.

In a similar way, observing the light emitted by a galaxy allowsscientists to measure the light’s wavelengths to determine whetherthe galaxy is moving and in which direction. This phenomenon is called the Doppler effect.

Analyzing the Colour of Light WavesAnother characteristic of star or galaxy light that astronomersanalyze is spectral pattern. When astronomers sample the light froma star or galaxy, a series of dark lines appears across its light spectrum.These spectral lines look similar to the bar code you see on retailproducts. Spectral lines are created as each gas that makes up astar absorbs some of the light energy. Each element does this in adifferent way, creating its own particular pattern of spectral lines(Figure 11.12). Because astronomers can see the spectral lines ofhydrogen in the spectra of nearly all celestial objects, it is clearthat hydrogen is present throughout the universe.


H(a) hydrogen

He(b) helium

Na(c) sodium

Ca(d) calcium

Fe(e) iron

Sun

Figure 11.12 Analyzing spectral lines in a star or galaxy’s spectrum indicates what elements are present.

(a)

(b)

Figure 11.11 By observing the patternmade by the waves, we can tell whetheran object is moving and whether it is moving toward or away from us. (a) When an object is hardly moving(stationary), its waves radiate outevenly in all directions. The distancebetween each wave, or wavelength, is the same. (b) When the object ismoving, the waves in front of it becomecompressed (the wavelength shortens)and the waves behind it stretch out(the wavelength lengthens).


Seeing Colours

Most humans are trichromatic,which means we have threereceptors in our eyes to see colour. Organisms thathave four receptors are knownas tetrachromats. They areable to see more of theelectromagnetic spectrum thanthe average human. Theseinclude birds and some insectsand reptiles. There are somehumans, mostly women, whoare tetrachromats as well.Some humans can bebichromatic or colour-blind.Both these conditions inhumans are genetically caused.

infoBIT Hubble and other astronomers noticed that for all of thegalaxies Hubble was studying, the spectral lines were shifted.Spectral shifting is the change in position of spectral lines to theleft or the right of where they normally are in the spectrum of alight source that is not moving. In all of Hubble’s observations,the spectral lines were shifted toward the red end of the spectrum.

Recall that red light has a longer wavelength than blue light at the other end of the spectrum. When light’s wavelength isincreased, the wavelength moves toward the red end of the visiblespectrum, or is red-shifted. This change in wavelength can beexplained by the Doppler effect. Recall the moving duck and thewavelength patterns it produces: wavelengths in front of the duckget shorter and wavelengths behind the duck get longer. Becausethe light spectra were red-shifted—that is, the light spectrawavelengths were longer—Hubble concluded that the galaxieswere moving away from the Milky Way (Figure 11.13).

If Hubble had instead found that the spectral lines wereshifted to the blue end of the galaxies’ light spectra, he wouldhave concluded that the wavelengths were shorter and morecompressed. Just as with the duck example, shorter wavelengthsbetween the observer and the moving object would have meantthat the galaxies were moving toward us, not away.


no shift

spectral lines

star is stationary

blue shift

red shift

star is approaching

star is moving away

Figure 11.13 If the spectral lines in the light from a star or galaxy occur toward the blue end of the light spectrum, it means the observer is seeing short wavelengths. This “blue shift”indicates that the star or galaxy is approaching the observer. However, if the spectral lines occurtoward the red end of the light spectrum, it means the observer is seeing long wavelengths.This “red shift” indicates that the star or galaxy is moving away from the observer.


When Hubble and other astronomers found this red-shiftpattern in an increasing number of galaxies, it supported the idea that the universe was expanding. Since then, much moreevidence has been collected.

The Keck telescope in Hawaii is one of the largest opticaltelescopes in the world (Figure 11.14). Astronomers recently usedthe Keck telescope to conduct a red-shift survey of galaxies, repeatingHubble’s work. This newer survey, called DEEP2, measured the light from 60 000 galaxies instead of 46. The results of theDEEP2 survey supported and added to Hubble’s original work.


Radiation Maps: More EvidenceA critical question related to the Big Bang theory remainedunanswered. The theory stated that the very early universe wasextremely hot and filled with short-wave gamma ray radiation.Then, as the universe rapidly expanded, it cooled and thewavelength of the radiation lengthened. The radiation becamelower energy types, including X rays, ultraviolet, visible light,infrared, and microwaves.

So, asked scientists, if the theory describing this series ofevents was reasonable, then where was the energy that shouldhave been left over from the very early moments of the formationof the universe? Their prediction was that all of space shouldcontain evidence of this radiation. Scientists set about to look for evidence of this residual radiation.

Figure 11.14 The Keck telescope in Hawaii


In 1965, two researchers, Arno Penzias and RobertWilson, made a big discovery—a discovery they were not even looking for (Figure 11.15). Their new microwaveantenna, intended for use in telecommunications, detectedthat the entire sky was bathed with microwave energy. Itcame from every direction, not just from individual stars.This energy is often called cosmic background radiation.Scientists believe it is the energy left over from the massiveand split-second expansion of the universe from a singlepoint some 13.7 billion years ago.

In 1992, the Cosmic Background Explorer satellite(COBE) made detailed maps of the background radiation

collected from the most distant parts of the visible universe. This was followed in 2006 when the Wilkinson MicrowaveAnisotropy Probe (WMAP) took even more precise measurementsof the radiation and created a much-enhanced map (Figure 11.16).

Both the COBE and the WMAP resultsshowed that the spectrum of the backgroundradiation precisely fits the predictionsconsistent with the Big Bang theory.

In science, although a theory can be supported by evidence, it is neverconsidered to be proven correct. If newevidence conflicts with a theory, scientistsmay need to rethink or revise the theory.This happens quite often. This is whythere are so many theories and so few

laws in the field of science. In this way, the COBE and WMAPsurveys not only back up the Big Bang theory, but they also showthat other theories of the formation of the universe cannot besupported. One of the theories not supported is the Steady Statetheory, which suggests that the universe is infinitely old and thatmatter and energy constantly enter and leave the universe atequal rates. To date, the Big Bang theory continues to be the only theory for the universe’s formation that is supported by the entire body of scientific information gathered so far.


Learning Checkpoint

1. What is wavelength? How is wavelength related to energy?

2. In your own words, define spectral shifting.

3. What is cosmic background radiation?

Figure 11.15 It was while using theHorn Antenna, located in New Jerseyin the United States, that radioastronomers Penzias and Wilsonunexpectedly discovered themicrowave background radiationpresent in every part of the sky.

Figure 11.16 The universe’s cosmicbackground radiation, mapped by the Wilkinson Microwave AnisotropyProbe (WMAP). The tiny variations inthe radiation are thought to indicatehot regions, now mostly empty space,and cooler regions, where mattercould collect to form the first galaxies.


Explaining Planetary MotionIn addition to developing theories that explain the origin of theuniverse, humans have also attempted to explain the motions of celestial bodies and our place in the solar system. From ourperspective on Earth, everything in the sky appears to be inmotion. The Sun rises and sets. The Moon, in its ever-changingphases, travels across the sky. Planets shift against a backgroundof stars. Even constellations appear to change position.

Just as we use what technology and science we have to answerquestions about the world around us, so our ancestors used theknowledge and technology they had to make sense of the constantchange they observed in the sky. Not surprisingly, it appeared toearly observers that all celestial bodies revolved around Earth.

Geocentric ModelMore than 2000 years ago, the widely held belief among astronomerswas that Earth sat at the centre of the universe. The ancient Greeksare best known for their models of the universe. The Ionians (6thto 4th century BCE) are credited with the idea that nature moves inpredictable ways, and were the first to build models based onobservations, not on supernatural explanations. TheIonian philosopher Anaximander proposed that Earthwas a cylinder at rest in the centre of the universe.This cylinder was surrounded by one or morespherical shells with holes in them. Theseholes appeared as stars because there was a fire that lay beyond the outer sphere.Models that have Earth at the centre of the universe are called geocentric models, or Earth-centred.

The philosopher and astronomer Aristotle is often mistakenly credited with the geocentric model. Although his modelhelped to explain how some objects, such as the Sun, Moon, and five planets, revolvedaround Earth (Figure 11.17), in his model, therewere 53 transparent rotating spheres above Earth. The Sun, Moon, and planets were embedded into these spheres. The stars were formed from a fifthelement, called quintessence, which was consideredincorruptible and eternal and lay beyond the spheres.


Fire

M o o n

Venus

Mer

cury

Sun

Mars

Jupiter

Saturn

Firmam

ent of fixe

d stars

Air Earth &Water

Figure 11.17 In the geocentric model, Earth was atthe centre and stars were thought to be fixed to theinside of the “celestial sphere,” like stars glued on theunmoving ceiling of a dome. Over time, with improvedobservations, this model was shown to be wrong.


The geocentric model continued to be developedby early scientists, including the Greek astronomerPtolemy in the 2nd century BCE. Ptolemy’s modelenabled the forecasting of many astronomicalphenomena, such as the changing phases of theMoon. Still, some observations of planetary motionwere puzzling. You know that the Sun moves acrossthe sky along a path known as the ecliptic. Planetsalso appear to follow a path close to the ecliptic.However, Mars, Jupiter, and Saturn appear to loopbackward for a period of days or weeks beforeresuming their normal path (Figure 11.18). This apparent backward motion is a celestialphenomenon known as apparent retrogrademotion. Various astronomers proposed changes tothe geocentric model to explain apparent retrogrademotion, but most of these adaptations wereextremely complicated.

Heliocentric ModelThe geocentric model of the solar system wasaccepted for almost 2000 years. The heliocentricmodel, which places the Sun at the centre, had beenproposed by the Ionian Greeks as far back as 500 BCE.Nicolaus Copernicus (1473–1543) reintroduced asimplified heliocentric model (Figure 11.19) inabout 1530, based on Ptolemy’s observations but not Ptolemy’s geocentric model. Copernicus’s modelplaced the Sun, stationary, near the centre of thesolar system and everything revolved around theSun, including Earth. This was a very radical idea at the time. Within the next 150 years, a newgeneration of scientists provided solid evidence for a slightly more complex heliocentric model.Notable among these scientists were the renownedGalileo Galilei (Italy), Johannes Kepler (Germany),and Sir Isaac Newton (England).

Two key ideas about planetary orbits helped add support to the heliocentric model. One was the relationship between aplanet’s orbital radius and its speed of orbit. The other was thefact that planetary orbits are elliptical and not circular.


Figure 11.18 This composite image of Mars was taken in2003 over the course of two months. It clearly shows thephases of the planet in apparent retrograde motion.

Sun

VenusMoon

Mercury

Mars

Saturn

JupiterEarth

Figure 11.19 The heliocentric model of the solar system put the Sun at the centre of the universe. At the time, it was considered to be an outrageous idea.


Orbital RadiusIn the heliocentric model, all planets orbit the Sun in the samecounterclockwise direction but at different distances. A planet’sdistance from the Sun is called the planet’s orbital radius. Theshorter the orbital radius, the faster the planet moves in its orbit.Therefore, Earth, which is closer to the Sun than Mars, orbits theSun more quickly than Mars. This is not just because Earth’sorbit is shorter than Mars’ orbit. Earth is also moving faster thanMars. In turn, Mars is moving faster than Jupiter, the next planetout from the Sun. This pattern is true for all the planets, dwarfplanets, and even asteroids in the solar system. The reason is that the farther an object is from the Sun, the weaker is the effect of the Sun’s gravity on that object.

Apparent Retrograde MotionThe differences in orbital speeds explainwhy Mars, Jupiter, and Saturn sometimesappear to have retrograde motion to anobserver on Earth. Earth orbits the Sunfaster than the other three planets. Forexample, at times, Earth overtakes Mars inits orbit around the Sun. It appears to anobserver on Earth that Mars is movingeastward across the sky, stopping, andmoving westward before stopping again and resuming its eastward motion (Figure 11.20). This change in direction is just an optical illusion. To help visualizehow apparent retrograde motion occurs,imagine you are in a track race. You pass three other runners, not only because you are moving faster, but also because you have the inside turn position. When you pass the other runners,they appear to be moving backward relative to you.

Geocentric models attempted to account for apparent retrogrademotion but were too complex. Heliocentric models, however, werebetter able to explain apparent retrograde motion. This was keyevidence in support of heliocentric models of the solar system.

Elliptical OrbitsEarly heliocentric models could still not predict planetary motionvery accurately. These models assumed that planets had a circularorbit. A circle has a single focus point—the centre. If the Sunwere placed in the centre, astronomers’ predictions of planetarymotion did not match their observations.


Earth’s orbit is elliptical, which means that the distancebetween Earth and the Sunchanges as Earth movesthrough its orbit. The shape of the orbit itself has alsochanged, and because of this,the date when Earth is closestto the Sun has also changed.Research how this affects thelength of the year over time.

reSearch

55

1MarsEarth

2

4

32

3

1

4

Figure 11.20 About every two years, Earth catches up to Mars andpasses it. This makes Mars appear to lag for a while, tracing a backward path against the starry background.



1. List Edwin Hubble’s two main discoveries.How did they change the way astronomersthought of space beyond our universe?

2. According to the Big Bang theory, how didthe universe originate?

3. When we view a celestial body from Earth,how we view and track the object oftendepends on the shape of the object’s orbit.Using Kepler’s explanation of orbits,explain the differences in the shape of the orbits in our solar system.

4. What does the visible light spectrum refer to?

5. Why is the understanding of the wavenature of light important to astronomers?

6. What is the difference between spectralshifting and red shifting?

7. What information can be gathered byobserving space for spectral shifting?

8. How does the idea that the universe isexpanding relate to the observation that thespectra from distant galaxies are red-shifted?

CHECK and REFLECT11.2

9. How is it possible to know that the elementhydrogen exists throughout the universe?

10. Explain how the discovery and mapping of cosmic background radiation gavescientists evidence in support of the Big Bang theory.

11. Astronomers often use models to explaintheories.

(a) In your own words, explain what anastronomical model is.

(b) Why might scientists need to use models?

12. What is the main difference betweengeocentric models and heliocentric models?

13. Using the geocentric and heliocentricmodels as examples, explain how theoriesmay change based upon the work of otherscientists.

14. In your own words, define apparentretrograde motion. How many celestialbodies are involved in apparent retrogrademotion? Explain.

In 1609, German mathematician JohannesKepler finally came up with the next piece ofthe puzzle. Using detailed observations madeby Danish astronomer Tycho Brahe, Keplerrealized that the orbits of the planets wereellipses (Figure 11.21).

An ellipse is somewhat like a slightlyflattened circle. Unlike a circle which has only one focus point, an ellipse has two focus points. If the Sun were placed at one of the two focus points, then astronomers’predictions and observations matched. This

was another key piece of support for the heliocentric model.Today, all astronomical observations continue to support

the heliocentric model of our solar system. It is also the guide we use when studying other star-and-planet systems.

Sun’s position

Planet’s path

Figure 11.21 The planets orbit the Sun in slightly elliptical, notcircular, orbits.


391Chapter 11 Our understanding of the universe is culturally influenced.©P

D22 Inquire on Your Own Activity

Astronomers proposed different models of planetarymotion to help explain celestial phenomena, such as the changing phases of the Moon and apparentretrograde motion. Two very important ideas in thedevelopment of models of planetary motion are orbital radius and elliptical orbits.

QuestionHow can you model celestial phenomena usinggeocentric and heliocentric models of planetary motion?

Design and Conduct Your Investigation1. Working in small groups, brainstorm ideas about

how you will create geocentric and heliocentricmodels of the solar system. As you generateideas, consider the following questions:• Which celestial bodies will you need to

include in your model? • How big does your model need to be?

Does it have to be to scale?• How will the celestial bodies in your model

maintain consistent orbital distances fromthe centre?

• How can you ensure that celestial bodiestravel at a consistent speed?

• How will you record celestial phenomena as viewed from the position of Earth? Can cameras be used?

• How can you incorporate the ideas of orbitalradius and elliptical orbits into your model?

Modelling Planetary Motion

SKILLS YOU WILL USE■ Designing, building, and testing■ Suggesting modifications

Toolkit 3

3. Select a design and write a procedure to buildyour models. Include a list of materials andequipment you will need.

4. Ask your teacher to approve your designs beforebeginning construction.

5. Build your models according to your design. Makesure to document any changes you make to theprocedure or the materials and equipment list.

6. Test your design by modelling a few rotations.Adjust your design, making note of any changesyou make.

7. Use your design to model the changing phases of the Moon and the apparent retrograde motionof Mars, Jupiter, and/or Saturn. How can thesephenomena be explained according to thegeocentric model? the heliocentric model? If necessary, adjust the design of your models and make note of any changes you make.

8. Present your final geocentric and heliocentricmodels in the format of your choice. Describe thecelestial phenomenon you chose and show howyour models explain the celestial phenomenon.

9. Consider how you could refine your investigationif you were to repeat it. Discuss your suggestionswith your group or as a class.

Key ActivityDI


392 UNIT D Exploring Our Universe

Key Concept Review1. How are First Nations and Métis peoples’

ideas of the creation of the universe basedon their knowledge of their environment?

2. Using the creation of the universe as anexample, explain how a person’s culturemay influence their explanations of theworld around them.

3. Why do scientists find the use of models so important?

4. What did Edwin Hubble discover about themotion of the 46 galaxies he first studied?

5. How did Hubble’s discovery provideevidence for what Georges Lemaître hadproposed about the universe?

6. How old is the universe thought to be?

7. Does red light in the visible light spectrumhave a longer or a shorter wavelength thanblue light?

8. (a) Make a sketch to illustrate what scientificastronomers mean when they say thatlight from a distant galaxy is red-shifted.

(b) What does a large red shift indicateabout a galaxy’s motion?

9. Explain how cosmic background radiationsupports the Big Bang theory of how theuniverse formed.

10. (a) Scientific astronomers have learned in recent decades that the most distantgalaxies from the Milky Way are movingaway from us. Use the library or theInternet to research the rate at whichthese galaxies are moving away from the Milky Way.

(b) What does your answer to part (a) suggestabout the universe?

11 CHAPTER REVIEW

11. Imagine you are standing on a shore and thereis an invisible duck swimming on a calmpond. For each example (a) and (b) shownbelow, state whether the duck is swimmingtoward or away from you. Explain how youknow the direction of its movement.

(a)

(b)

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Question 11

12. What technological development played animportant part in gathering support for theheliocentric model? How was it helpful?

13. Describe the geocentric and heliocentricmodels of the universe in terms of theposition and movement of the Sun, Earth,and the stars.

14. Explain how elliptical orbits and betterexplanations of apparent retrograde motion provided evidence to support theheliocentric model of the solar system.

Connect Your Understanding15. You have learned two scientific theories:

the Big Bang theory and the heliocentricmodel of the solar system. Choose onetheory and explain how this theory wasdeveloped. Be sure to include observationsthat were made, developments in technology,and evidence that supports the theory.Present your findings using a format ofyour choice, such as a graphic organizer,timeline, written paper, or presentation.


16. Most evidence collected by scientists so farsupports the Big Bang theory of the originand formation of the universe. All otherscientific theories to explain the origin haveso far largely been disproven by scientificevidence. If you were a scientist, would youagree or disagree with the statement: “TheBig Bang theory is correct because it is thelast theory standing”? Explain the reasonfor your answer.

17. Scientists speculate that trillions of yearsfrom now, galaxies will have moved awayfrom our galaxy faster than their light can reach us. Our region of space, like allother regions, will be left in the dark. Is this something we should plan for onEarth? Explain.

18. Humans have attempted to explain the originof the universe and our place in it from bothcultural and scientific perspectives. Howare the explanations similar? How are they different?

19. Another type of retrograde motion isretrograde rotation. Use library or Internetresources to research retrograde rotationand which planets undergo this type ofretrograde motion. Present your findings in the format of your choice, such as aposter, written report, or presentation.

Reflection20. Think about the activities in this chapter

that you carried out. Make a list of the ones you did or observed your teacherdemonstrating. Beside each activity, writedown two points you learned from it thathave helped you better understand theconcepts presented in the text.

21. Many of the activities in this text suggestthat you brainstorm in a small group or as a class. What benefits do you think a groupapproach offers in terms of helping toadvance ideas about a topic?

393Chapter 11 Review©P

Reflection on Essential Inquiry Questions

How has the way we explain what is occurringin our solar system and universe changed?What has caused these changes?

How do different understandings of theuniverse affect how we explore it?

How have advances in technology lead todifferent theories on how the universe may have formed?

How is making sense of the universe culturallyinfluenced?

Unit Task

Technology is now allowing humans to exploreour solar system and universe in new andexciting ways. As more information is gathered,our knowledge grows. Canada is not only aleader in development of space technology, butalso a contributor to the understanding of ouruniverse. How will a greater understanding ofthe creation or nature of the universe be usefulin completing your Unit Task?

CP

DM

TPS

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Reflect and Evaluate

Summarize the “improve your understanding”strategies you learned to use in this chapter.Working with a partner, create a tips sheet for otherreaders about improving understanding when theyare reading. Add other strategies that you haveused successfully to understand what you read.

After Reading

22. For each of the following topics, describethree facts that you learned in this sectionthat you did not know before:

(a) formation of the universe

(b) structure of the universe

(c) evolution of the universe


11 our understanding of the universe

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