This is the Physical Science Quarter 2 Module 8, Expanding Universe, a Senior High School self-learning module (Alternative Delivery Mode, First Edition 2020) from DepEd National Capital Region. It has one lesson, Astrometry and Cosmology. It explains how scientists estimate the distance and speed of stars and galaxies, and what evidence shows that the universe is expanding and is about 14 billion years old.
On this page 6 sections
What learners will learn
Content standard: Learners demonstrate an understanding of Relativity and the Big Bang.
Performance standard: Learners create a video presentation that details the impact of the Theory of Relativity on humans.
Learning competencies (S11/12PS-IVj-72-73): Explain how the speeds and distances of far-off objects are estimated (for example, the Doppler Effect and the Cosmic Distance Ladder), and explain how we know that we live in an expanding universe that used to be hot and is about 14 billion years old.
After the module, learners should be able to:
- Explain the different ways the speed and distance of celestial objects are estimated.
- Explain the various pieces of evidence for the theory of an expanding universe.
Key ideas: measuring distance and motion in space
The lesson starts with two branches of astronomy. Cosmology studies the origin and evolution of the universe. Astrometry measures the distances and motion of celestial bodies.
The Cosmic Distance Ladder
The Cosmic Distance Ladder is a series of methods used one after another. Each rung measures a certain range of distance, and its results help measure the next, farther rung.
- Early Greek measurements: Aristotle concluded that the Earth and Moon are spherical. Eratosthenes calculated Earth’s radius to within 8%. Aristarchus made the first recorded measurement of the Moon’s distance and estimated the Sun’s size.
- Astronomical Unit (AU): the average distance from the Earth to the Sun. It was first found by observing the transit of Venus and is now measured with telemetry.
- Radar ranging (first rung): radar pulses are sent to an object in the Solar System. The time it takes for the reflected pulse to return gives the distance.
- Parallax: the apparent shift in an object’s position when seen from two lines of sight. You can see it by holding up a finger and closing each eye in turn. Astronomers compare views of a nearby star taken six months apart, from opposite sides of Earth’s orbit. Nearer stars shift more. Trigonometric parallax is accurate for distances under 100 parsecs.
- Units: a light-year is the distance light travels in one Julian year (365 ¼ days), about 9.46 x 10^12 km. One parsec equals 3.26 light-years.
- Standard candles: objects whose true brightness (luminosity) is known. The module compares them to street lamps of equal power: a lamp that looks ¼ as bright is twice as far away.
- Cepheid variable stars: stars that brighten and dim over days to months. In 1912, Henrietta Leavitt found that Cepheids with longer periods are more luminous. This lets astronomers measure distances up to about 100 million light-years. White dwarf supernovae are used for even farther galaxies.
Spectral lines and the Doppler Effect
Each element gives off its own pattern of spectral lines, like a fingerprint. The Doppler Effect changes how these lines appear. With sound, a siren’s pitch rises as it comes closer and falls as it moves away. With light:
- A source moving toward you is blue-shifted (shorter wavelengths), like the headlights of a car coming toward you.
- A source moving away from you is red-shifted (longer wavelengths), like the taillights of a car driving away.
The spectral lines of distant stars are shifted toward red, which shows that those stars are moving away from us.
Key ideas: evidence for an expanding universe
Hubble’s Law says that the farther a galaxy is, the faster it moves away from the observer. Because galaxies are moving farther away, and faster, scientists accepted the idea of an expanding universe.
The module has learners model this with a balloon:
- Draw dots on a deflated balloon and label one of them as the reference dot (1).
- Measure the distance from the reference dot to each of the other dots.
- Inflate the balloon and measure again, then compare the two sets of distances.
A raisin-bread model shows the same idea. As the loaf rises, every raisin moves away from every other raisin, and the ones that are farther apart separate faster.
The Big Bang Theory explains how the universe expanded from a very dense, hot state. Besides Hubble’s observations, the module lists four other pieces of evidence:
- Cosmic background radiation: found in 1964 by Arno Penzias and Robert Wilson. It is leftover radiation from the early universe, measured at 2.75 K.
- Ratio of primordial elements: the measured amounts of hydrogen, helium, and trace elements match predictions from Big Bang nucleosynthesis.
- Formation of galaxies: galaxies and galaxy clusters keep being discovered, and their structures differ.
- Primordial gas clouds: clouds that contain only hydrogen and deuterium, thought to be remnants of the early universe.
How to use this module
The module follows the standard self-learning module parts, in this order:
- What I Know: a 10-item multiple-choice pretest. Answer it before anything else. If you get every item right, you may skip the module.
- What’s In: a review activity in which you decode words with a Pigpen cipher and match them to earlier astronomy topics.
- What’s New and What is It: the main discussion of the topics above.
- What’s More: Hubble’s Law, the balloon activity, and its guide questions.
- What I Have Learned: a summary of the key concepts.
- What I Can Do: two short essay questions. One asks whether you agree that you look back in time whenever you look at the stars. The other asks what you think the future of the universe will be.
- Assessment: the same 10 questions as the pretest.
- Additional Activities: a personal radar chart for rating your own understanding of the module.
For learners: Write your answers on a separate sheet, not on the module. Check your work honestly against the Answer Key at the end, and return the module to your teacher when you finish.
For parents: The balloon activity needs only a balloon, a marker, and a tape measure. You can help your child measure the distances and record them.
For teachers: The module asks you to show learners how to use it, track their progress, and support them as they work through the tasks. Before you share the Answer Key, check it against the lesson.
Frequently asked questions
What grade and quarter is this Physical Science module for?
It is for Senior High School Physical Science (Grade 11/12), Quarter 2, Module 8. It covers learning competency code S11/12PS-IVj-72-73.
What is the Cosmic Distance Ladder?
It is a series of methods that astronomers use one after another to measure the distances of stars and galaxies. Radar ranging is the first rung, followed by parallax, standard candles, and Cepheid variable stars. Each rung uses results from the one before it.
What does red shift mean?
Red shift means the light from a source is shifted toward longer, redder wavelengths. It shows that the source is moving away from the observer. Red-shifted light from distant galaxies is evidence that the universe is expanding.
What evidence for the expanding universe does the module give?
Besides Hubble’s Law, it lists four: cosmic background radiation, the ratio of primordial elements, the formation of galaxies, and primordial gas clouds that contain only hydrogen and deuterium.
Does the module have an answer key?
Yes. The Answer Key at the end covers the pretest (What I Know), the review activity (What’s In), and the Assessment.
Full text of the module
The text below is a transcription of the PDF above, as printed.
Physical Science Quarter 2 – Module 8: Expanding Universe
Senior High School
Physical Science Quarter 2 – Module 8: Expanding Universe
[illustration: students and a teacher studying together, with a globe, a lamp, and a tree; ADM logo below]
Physical Science Alternative Delivery Mode Quarter 2 – Module 8: Expanding Universe First Edition, 2020
Republic Act 8293, section 176 states that: No copyright shall subsist in any work of the Government of the Philippines. However, prior approval of the government agency or office wherein the work is created shall be necessary for the exploitation of such work for a profit. Such agency or office may, among other things, impose as a condition the payment of royalties.
Borrowed materials (i.e., songs, stories, poems, pictures, photos, brand names, trademarks, etc.) included in this module are owned by their respective copyright holders. Every effort has been exerted to locate and seek permission to use these materials from their respective copyright owners. The publisher and authors do not represent nor claim ownership over them.
Published by the Department of Education Secretary: Leonor Magtolis Briones Undersecretary: Diosdado M. San Antonio
Development Team of the Module
Writers: Angelo Gutierrez Cabic Editors: Joey H. Villanueva, Arlene C. Malaybalay Reviewers: Tommy R. Rico, Emiterio D. Macarubbo, Maricris N. Surigao Illustrator: Angelo Gutierrez Cabic Layout Artist: Justine C. Montoya Management Team: Wilfredo E. Cabral, Director IV Jennifer F. Vivas, CLMD Chief Dennis M. Mendoza, Regional EPS in-charge of LRMS Micah S. Pacheco, Regional ADM Coordinator Jocelyn M. Aliñab, CID Chief Tommy R. Rico, Division in-charge of LRMS and Division ADM Coordinator
Department of Education – National Capital Region
Office Address: Misamis St., Bago Bantay, Quezon City Telefax: 02-929-0153 E-mail Address: depedncr@deped.gov.ph
Physical Science Quarter 2 – Module 8: Expanding Universe
Senior High School
Physical Science Quarter 2 – Module 8: Expanding Universe
Introductory Message
For the facilitator:
Welcome to the Physical Science 11/12 Alternative Delivery Mode (ADM) Module on Expanding Universe!
This module was collaboratively designed, developed, and reviewed by educators to assist you, the teacher or facilitator in helping the learners meet the standards set by the K to 12 Curriculum while overcoming their personal, social, and economic constraints in schooling.
This learning resource hopes to engage the learners in guided and independent learning activities at their own pace and time. Furthermore, this also aims to help learners acquire the needed 21st century skills while taking into consideration their needs and circumstances.
In addition to the material in the main text, you will also see this box in the body of the module:
[illustration: icon of papers with a pencil]
Notes to the Teacher This contains helpful tips or strategies that will help you in guiding the learners.
As a facilitator, you are expected to orient the learners on how to use this module. You also need to keep track of the learners’ progress while allowing them to manage their learning. Furthermore, you are expected to encourage and assist the learners as they do the tasks included in the module.
For the learner:
Welcome to the Physical Science 11/12 Alternative Delivery Mode (ADM) Module on Expanding Universe!
Our hands are the most symbolized part of the human body. It is often used to depict skill, action, and purpose. Through our hands we may learn, create, and accomplish. Hence, the hand in this learning resource signifies that you as a learner is capable and empowered to successfully achieve the relevant competencies and skills at your own pace and time. Your academic success lies in your own hands!
This module was designed to provide you with fun and meaningful opportunities for guided and independent learning at your own pace and time. You will be able to process the contents of the learning resource while being an active learner.
This module has the following parts and corresponding icons:
| Icon | Part | Description |
|---|---|---|
| [illustration: hand icon] | What I Need to Know | This will give you an idea of the skills or competencies you are expected to learn in the module. |
| [illustration: pencil icon] | What I Know | This part includes an activity that aims to check what you already know about the lesson. If you get all the answers correct (100%), you may decide to skip this module. |
| [illustration: hands icon] | What’s In | This is a brief drill or review to help you link the current lesson with the previous one. |
| [illustration: leaf icon] | What’s New | In this portion, the new lesson will be introduced to you in various ways such as a story, a song, a poem, a problem opener, an activity or a situation. |
| [illustration: magnifying glass icon] | What is It | This section provides a brief discussion of the lesson. This aims to help you discover and understand new concepts and skills. |
| [illustration: steps icon] | What’s More | This comprises activities for independent practice to solidify your understanding and skills of the topic. You may check the answers to the exercises using the Answer Key at the end of the module. |
| [illustration: lightbulb icon] | What I Have Learned | This includes questions or blank sentences/paragraphs to be filled in to process what you learned from the lesson. |
| [illustration: hand with gears icon] | What I Can Do | This section provides an activity that will help you transfer your new knowledge or skill into real-life situations or concerns. |
iv
| Icon | Part | Description |
|---|---|---|
| [illustration: pencil and paper icon] | Assessment | This is a task which aims to evaluate your level of mastery in achieving the learning competency. |
| [illustration: gears icon] | Additional Activities | In this portion, another activity will be given to you to enrich your knowledge or skill of the lesson learned. This also tends retention of learned concepts. |
| [illustration: key icon] | Answer Key | This contains answers to all activities in the module. |
At the end of this module you will also find:
| Part | Description |
|---|---|
| References | This is a list of all sources used in developing this module. |
The following are some reminders in using this module:
- Use the module with care. Do not put unnecessary mark/s on any part of the module. Use a separate sheet of paper in answering the exercises.
- Do not forget to answer What I Know before moving on to the other activities included in the module.
- Read the instruction carefully before doing each task.
- Observe honesty and integrity in doing the tasks and in checking your answers.
- Finish the task at hand before proceeding to the next.
- Return this module to your teacher/facilitator once you are through with it.
If you encounter any difficulty in answering the tasks in this module, do not hesitate to consult your teacher or facilitator. Always bear in mind that you are not alone.
We hope that through this material, you will experience meaningful learning and gain a deep understanding of the relevant competencies. You can do it!
What I Need to Know
[illustration: hand pressing a button icon]
This module will help you understand the evolution and expansion of the universe through approximation of distance and movement of stars and galaxies. This module will provide you with discussions and learning activities designed to be easily understood.
CONTENT STANDARD: The learners demonstrate an understanding of Relativity and the Big Bang.
PERFORMANCE STANDARD: The learners should be able to create a video presentation that details the impact of the Theory of Relativity to human.
LEARNING COMPETENCIES: The learners must explain how the speeds and distances of far-off objects are estimated (e.g., Doppler Effect and Cosmic Distance Ladder) and explain how we know that we live in an expanding universe which used to be hot and is approximately 14 billion years old.
CODE: S11/12PS-IVj-72-73
- Lesson 1 – Astrometry and Cosmology
After going through this module, you are expected to:
- Explain the different ways in which the speed and distance of celestial objects are estimated; and
- Explain the various pieces of evidence for the theory of an expanding universe.
What I Know
[illustration: hand holding a pencil icon]
DIRECTIONS: Read each question carefully. Choose the letter of the best answer. Write your answer on a separate sheet of paper.
What is a light-year?
a. The distance travelled by light in one year (365 ¼ days)
b. The distance travelled by light in a leap year (366 years)
c. The time required for light to cover 1 AU of distance travelled
d. The time required for light to make a round trip from a nearby starWhat is the approximate age of the universe?
a. 14 million years c. 4.5 million years
b. 14 billion years d. 4.5 billion yearsWhat is an Astronomical Unit (AU)?
a. It is the average spacing of the planets.
b. It is the average distance of the earth from the Sun.
c. It is the average distance of the earth from the moon.
d. It is the average distance of the Sun from the nearest Star.What is a parallax?
a. An imaginary parallel line of reference when viewing distant stars.
b. A unit of measurement of the displacement of celestial objects due to atmospheric factors.
c. An apparent displacement of the observed position of objects viewed from different lines of sight.
d. A pulsing of light emitted by stars that are at least 1200 Light-years away from the Solar System.Which part of the spectrum does the Starlight show a shift in wavelength?
a. Infrared ends of the EM Spectrum
b. Red light ends of the visible spectrum
c. Blue light ends of the visible spectrum
d. Ultraviolet-ray ends of the EM spectrumWhich is TRUE about the movement of galaxies observed from earth?
a. Far galaxies tend to move faster towards observers on earth.
b. Far galaxies tend to move slower towards observers on earth.
c. Far galaxies tend to move faster away from observers on earth.
d. Far galaxies tend to move slower away from observers on earth.What do red-shifted lights mean?
a. The source is slowing down.
B. The source is moving towards the observer. C. The source is moving away from the observer. D. The source is moving perpendicular to the observer.
What does the redshifted light from a distant galaxy tell about the universe?
A. It indicates that the universe is shrinking.
B. It indicates that the universe is expanding.
C. It indicates that the universe is not shrinking nor expanding.
D. It indicates that the universe is shrinking and expanding in cycles.The diagram on the right shows the comparison between the standard spectrum of an element and a spectrum produced by a distant star. What conclusion can be drawn from this?
A. The distant star collapsed.
B. The distant star is approaching the earth.
C. The distant star is moving away from the earth.
D. The distant star is following an elliptical movement.
[chart: spectrum comparison; Standard Spectrum. Labels: Spectral lines; Ultraviolet; Visible light; Infrared]
[chart: spectrum comparison; Spectrum from Distant Star. Labels: Spectral lines; Ultraviolet; Visible light; Infrared]
- The figure below shows the spectral lines from an element in a laboratory.
[chart: spectral line diagram; spectral lines from an element in a laboratory. Labels: VIOLET; RED]
Which diagram best illustrates the spectral lines when the light is observed from a distant star moving away from the earth?
A. [chart: spectral line diagram; option A. Labels: VIOLET; RED] B. [chart: spectral line diagram; option B. Labels: VIOLET; RED] C. [chart: spectral line diagram; option C. Labels: VIOLET; RED] D. [chart: spectral line diagram; option D. Labels: VIOLET; RED]
Lesson 1 Astrometry and Cosmology
[photo: Milky Way Galaxy above a beach at night, with a person standing near the shore. Photo Credits: Alexis Gapal]
On a trip to Lobo, Batangas in 2017, a photography enthusiast tried to take a shot of the Milky Way Galaxy, where our Solar System is located. After several tries, his efforts paid off and the result is this magnificent unedited photo of the galactic core of the Milky Way.
When we look at the night sky, especially during star gazing activities, we would normally wonder how far are the stars from earth.
Our universe is not static. It has been evolving for billions of years from the time of the Big Bang. As time progresses, the matter was produced from the very small quarks, atoms, and elements to very large such as planets, stars, and galaxies. These galaxies move relative to each other and hence, change their position as observed here on earth. But how do scientists know that these stars and galaxies are moving?
Cosmology is the branch of astronomy that deals with the origin and evolution of the universe. Astrometry on the other hand is the branch of astronomy involved in the measurement of distances and motion of celestial bodies. These two branches are related.
This module will help you understand how scientists were able to approximate the distances and movement of stars and galaxies in our universe. This material will also help you recognize the different pieces of evidence to prove that our universe is expanding since it was hypothesized to have existed 13.8 billion years ago.
What’s In
In the previous modules, you were introduced to the contributions of various scientists in the development of early astronomical concepts. As a review, use the Pigpen cipher below to decode the words listed in the table. Choose from the options below the corresponding description of the decoded words. Write your answer in alphabetical order.
[illustration: Pigpen cipher key showing letters A to Z in grids and X-shaped symbols]
| Words for Decoding | Decoded Words | Description |
|---|---|---|
| [illustration: pigpen cipher symbols] | ||
| [illustration: pigpen cipher symbols] | ||
| [illustration: pigpen cipher symbols] | ||
| [illustration: pigpen cipher symbols] | ||
| [illustration: pigpen cipher symbols] |
Description Options:
A. He is credited for formulating the laws of Planetary Motion. B. It happens during March and September when the length of daylight and nighttime are approximately equal. C. He published a revolutionary paper contradicting the widely accepted Earth-centered model of the Solar System. D. The two days in a year in which the Sun is at the farthest declination (north or south) from the celestial equator. E. He is an advocate of the Geocentric or Earth-Centered model of the Solar System.
What’s New
First few steps of the Cosmic Distance Ladder
Even without the aid of sophisticated tools, early scientists were able to make many meaningful approximate measurements in astronomy. By observing the circular arc-shaped shadow casted by the earth on the moon during lunar eclipse, and the shape of the phases of the moon, Aristotle (384-322 BCE), was able to tell that the earth and the moon is spherical. Eratosthenes (276-194 BCE) used geometry with a lot of observation to calculate the radius of the earth which is accurate within 8% of the actual radius of the earth. Aristarchus (310 – 230 BCE) was also responsible for making the first documented measurement of the distance of the Moon from the Earth, as well as , the approximate radius of the moon. Aristarchus was also credited for his approximation of the size of the sun which also lead him to propose that the earth revolves around the sun, rather than the sun revolving around the earth (which was the long standing belief). Among these discoveries, it is important to note that the succeeding measurements and approximations were done by using data obtained from previous observations. Such that measurements for the moon were obtained by using measurements made for the earth, and measurements for the sun were obtained using measurements from the moon and the earth.
[illustration: Artist’s conception of a cosmic distance ladder extending past a spiral galaxy and a nebula. Figure 1. Artists conception of Cosmic Distance Ladder. From: https://images.app.goo.gl/NsDdEr4AQXKKEVgM7]
The Cosmic Distance Ladder is a series of successive methods used by astronomers to determine the distances of distant celestial bodies such as stars and galaxies. In this method, one rung or step of the ladder correspond to a process done to measure certain ranges of distances, to which information gathered in this step can be use to obtain approximate measurements of the next higher rung.
The measurements done on earth during the time of the early Greeks served as the first foundations of the cosmic distance ladder. With the development of modern astronomy, more sophisticated devices and methods yielded more accurate measurements on the earth’s size. Scientists used the term Astronomical Unit (AU) – the average distance of the Earth from the Sun which is now measured to be 1. 498 x 10^8 km. Originally, this value was obtained by careful observations of the transit of Venus across the sun as its backdraft. Now, more accurate measurements are made using telemetry – the process of recording and transmitting readings of a network of instruments.
In considering measurements of distances within the solar system, Radar Ranging is used. As depicted in figure 2, Radar pulses in the form of EM waves will be sent from earth towards the target celestial object. This pulse will be reflected from the target celestial object to the earth. The time of the reflected pulse to be detected back on earth will be recorded to calculate the approximate distance of the target celestial object. Radar ranging serves as the first rung or step in our cosmic distance ladder. This is used to determine the distance of objects in the Solar System.
[illustration: Radar ranging; labels: Radar Pulse, Reflected Pulse. Figure 2: Radar Ranging. Artwork: A.G. Cabic]
What is It
Going Beyond the Solar System
The next rung in the Cosmic Distance Ladder is the use of Parallax – the apparent displacement or difference in the apparent position of an object viewed along two different lines of sight. This can be demonstrated in Figure 3.
[illustration: a finger held in front of a building and trees, seen by the left eye and by the right eye; labels: Seen by your Left Eye, Seen by your Right Eye. Figure 3: Demonstrating Parallax. Artwork: A.G. Cabic]
Extend your arm and look at your finger with a distant background, with one of your eyes closed. You will notice that when you focus at your finger (closer object of interest) while having a distant object as background, the image of your finger appears to shift positions relative to the background when you use only one eye alternately. This apparent “shift” in the position of the object of interest is due to the change in the position of the observer (your right and left eye respectively).
As applied to astrometry, astronomers use trigonometric parallax to calculate the distance of a relatively nearby celestial object such as a nearby star (other than the sun). This is done by comparing observations of a nearby star that are taken six months apart. The nearby star appears to be displaced against the background of farther stars because the observations were taken from two opposite points of Earth’s orbit around the sun. Figure 4 shows how this is done. Upon careful analysis, you will notice that nearby objects tend to have greater “shifting” or parallax, while more distant objects tend to have smaller “displacements”.
[illustration: diagram of Earth’s orbit around the Sun at points E and E’, with a near star and distant stars; labels: Sun, E, E’, Near star, Distant stars, α. Figure 4: Using Parallax to Measure distance. Image from: https://images.app.goo.gl/D677gK84BSiwgeV26]
When using parallax, the units of measurement commonly used is light-year, the distance travelled by light in one Julian Year (365 ¼ days) and parsec, the distance of which the mean radius of the earth’s orbit subtends an angle of one second of arc. One light-year is 9.46 x 10^12 km while 1 parsec is equivalent to 3.26 light-years. Trigonometric parallax can only be accurate for distances less than 100 parsecs. There are also other kinds of parallaxes, however, these are not as accurate as the trigonometric parallax. For distances greater than 100 parsecs to 10,000 parsecs (halfway across the Milky Way), it requires combination of such parallaxes to make more accurate measurements.
Standard Candles and Cepheid Variable Stars
[photo: street lamps and a lit Ferris wheel along a waterfront promenade at night. Fig. 5: Street lamp lights in Puerto Princesa, Palawan. Image source: https://web.archive.org/web/20161024200642/http://www.panoramio.com/photo/87990544]
With the development of techniques in measuring stellar brightness, approximating distances of stars in the Milky Way Galaxy relied on Standard Candles – objects with known luminosity. In using standard candle methods, it is important to group stars according to their distinct properties such as absolute and apparent magnitude (which in turn is related to the luminosity). The inverse square law can be use to determine the distance of the star from the earth. A good analogy to this is by observing the light emitted by streetlamps at night. Assuming that each lamp is of the same power rating, if one lamp appears ¼ as bright as another, then we can say that the dimmer one is twice as far as the brighter lamp; if the lamp is three times farther, it’s expected to be 1/9 as bright as the closer lamp (See Figure 5). The challenge of measuring astronomical distances using standard candles is to find objects that makes the best standard candle such that we can accurately identify its magnitude or luminosity.
Among the standard candles available, the most useful for nearby galaxies are special classes called Cepheid variable stars or Cepheids. These stars vary in luminosity alternately appearing to be dim and bright with intervals from a few days to a few months. Henrietta Leavitt in 1912 discovered that when Cepheids have longer periods of alternating brightness, the more luminous it become. Combining it with parallax measurements on Cepheids, and data on their apparent brightness, it became possible to calculate its true luminosity and identify the distance from such data. It was also observed that this period of alternating brightness of Cepheids is also related to its size. Larger Cepheids takes longer intervals of alternating brightness. Cepheids can be used to approximate the distance of stars and Galaxies up to 100 million light-years away. Like Cepheids, White dwarf supernovae can also be used to measure distances of very far galaxies. This is due to the idea that they all have the same peak luminosity because they originated from the same sizes of main sequence stars.
Through studies done on elements, scientists were able to determine that elements and molecules emit specific kind of absorption and emission lines. Each type of atom and molecule possesses a specific and unique set of energy levels, causing the production of emission and absorption lines appearing in certain wavelengths of the spectra. In a way, these emission and absorption line patterns serve as a form of fingerprint to identify the elemental composition of a material – including stars!
[chart: spectra diagram; Fig. 6: Continuous Spectrum and Emission lines of various elements. Labels: Continuous spectrum; Sodium; Hydrogen; Calcium; Mercury; wavelength axis: 4000 Å, 5000, 6000, 7000. Image source: OpenStax Astronomy 2018 page 164]
Doppler Effect
You might have experienced hearing the sound of siren from an approaching ambulance or train. You noticed that as the source of sound approaches your location, the sound emitted by the source become louder.. As the source moves away from your location, the sound gradually fades. This is a manifestation of Doppler Effect.
[illustration: three panels of concentric sound waves from a stationary alarm clock, an alarm clock moving toward a listener, and an alarm clock moving away from a listener. Figure 7. Doppler Effect for Sound. Artwork: A.G. Cabic]
Doppler Effect.
Figure 7 which shows the Doppler effect for sound. (Left) When the source is stationary, the observer would not notice any change in wavelength of the sound waves, thus, no change in frequency and no change in pitch. (Middle) Once the source of sound moves, the region being approached by the source will have more compressed wavelengths of sound, hence, greater frequency and an increase in pitch is observed.(Right) When the source is moving away from the observer, there will be a region where the sound waves are not compressed; hence, longer wavelengths of sound corresponding to a decrease in pitch.
Doppler Effect is also observed in light and when this happens, the wavelength of light from sources such as flashlights, light bulbs or even stars will be affected. Once the wavelength of light is affected, there will be changes in the observed colors of light. When the source of light is moving towards the observer, the observed light
turns Blue shifted or shifted towards the short wavelength portion of the spectrum. When the source of light is moving away from the observer, the observed light becomes Red Shifted or shifted towards the long wavelength portion of the spectrum. As an analogy, the headlights of cars appear bluish when the car is approaching you. The taillight of cars appears reddish when the car is moving away from you.
[chart: spectral line comparison; Fig. 8: Shifting of spectral patterns from spectral lines from stars. Notice that it is shifted towards the Long wavelength (Red) end, and thus the term red shift. Artwork: A. G Cabic. Rows: HYDROGEN (Laboratory); HYDROGEN (Stellar); HELIUM Laboratory; HELIUM (Stellar). Axis labels: 4000 Å; 5000 Å; 6000Å; 7000 Å; VIOLET; RED]
Figure 8 shows a simplified spectral line comparison between a normal spectral line pattern observed in a laboratory and a spectral line pattern from a star. The patterns from stars appears to be shifted to the Red end, and thus Red-Shifted. This indicates that the star being observed is moving away from the observer on earth.
The methods that were discussed enabled scientists to determine two things. First, the continuously expanding measurements of distances from the closest neighbors in the solar system to the most distant stars in the outskirts of the Milky way galaxy, as well as other galaxies and galaxy clusters in the universe. Second, the stars, and galaxies are moving as indicated in the Red Shift of light coming from these stars and galaxies. All of these were approximately measured by using the previous rungs or steps in the cosmic distance ladder to arrive at more advanced steps.
What’s More
Hubble’s Law and the Expanding Universe
Edwin Hubble’s discovery of the Andromeda Galaxy enabled him to study for the Milky Way Galaxy. This made scientists believe that the Milky Way is only a small portion of a larger universe. What is more interesting in Hubble’s findings is the fact that as galaxies and stars get farther and farther, it tends to move faster away from the observer. This relationship between the distance of the star or galaxy is observed to its recession speed (speed at which it is moving away) is called Hubble’s Law. Sometimes, this relationship is also used in reverse. By knowing the recession speed of the galaxy (through redshift calculations), one can approximately determine the distance of a star or a galaxy from the earth. Having observed that galaxies are moving farther, and faster, this led to the well-accepted idea of an Expanding Universe. But how do we visualize an expanding universe?
Activity:
Put 3 or more dots on a deflated balloon.
From the markings, select one reference dot and mark it as 1. Mark the rest of the dots as 2, 3, etc.
Use a tape measure to measure the distances between the reference mark and the other markings. Record your measurements.
Inflate the balloon and tie its end to maintain its size. Using the reference mark, re-measure the distances of the other markings from the reference. Record your observation and compare it with the measurements when the balloon is deflated.
[illustration: markings on a deflated balloon (left) and an inflated balloon (right)]
Figure 9. Markings on a deflated balloon (Left) and inflated balloon (Right) Artwork: A.G. Cabic
| Markings | Distance from 1 Deflated Balloon | Distance from 1 (Inflated Balloon) |
|---|---|---|
| 2 | ||
| 3 | ||
| 4 | ||
| 5 |
Guide Questions:
- What have you observed on the distances of the dots/markings between a deflated balloon and an inflated balloon?
- What caused the difference in the distances of the markings between a deflated and an inflated balloon?
- If you will compare the balloon to our universe, with the dots / markings as galaxies or galaxy clusters, what can you say about the distances of the galaxies as continuously expands?
The previous activity simulates how scientists model our expanding universe. This is like a raisin-bread loaf model, shown in Figure 10. Notice that when the bread is still small, the raisins are close to each other. As the bread expands due to more yeast added, the distances between the raisins also increase.
[chart: diagram; Figure 10. Raisin Loaf bread analogy for an expanding universe]
Labeled distances printed in the diagram: 3 cm, 7 cm, 16 cm, 20 cm, 30 cm (small loaf); 6 cm, 14 cm, 32 cm, 40 cm, 60 cm (large loaf).
Figure 10. Raisin Loaf bread analogy for an expanding universe Image source: OpenStax Astronomy 2018 page 958
The rate at which the raisins move away from each other is proportional to the distance of separation of the raisins. This is the same with the galaxies and galaxy clusters in our known universe. The farther they are from a point of observation, the faster they move away from the observer.
The concepts discussed in the first part of this module are some of the main arguments that the universe is expanding. But since there are pieces of evidence of its expansion, then it also follows that there should be a description of the state of the universe on its early stages from the beginning. The theory which explains how the universe expanded from a highly dense and hot state is what we call the Big Bang Theory. Aside from the observations made by Hubble, the following are other observational evidence of the expansion of the universe:
Cosmic Background Radiation – in 1964, Arno Penzias and Robert Wilson discovered strange “noises” in their Radio telescope observations. The noises turned out to be the remnants of the original radiation emitted by the expanding universe. Since the universe was initially very dense and very hot prior to its expansion, 14 billion years after, the universe should have cooled down. They measured this background radiation to be 2.75 K.
Ratio of Primordial Elements – during the early state of the universe, early elements such as hydrogen and helium, fuse to form new elements (Big Bang Nucleosynthesis), the same as how stars generate their energy through thermonuclear fusion. As time progresses, the ratio of elements should be proportional. Astronomers measure the ratios of hydrogen, helium, and other
trace elements. It turned out that the present ratio of elements is in accordance with the predictions made.
Formation of Galaxies – if the Big Bang is true, then there should be a great number of galaxies and galaxy clusters out there. Continuous discoveries of galaxy formation across the universe and differences in the structure of these galaxies also serve as strong evidence that the Big Bang really exists.
Primordial Gas Clouds – recently formed galaxies should contain a good mix of light and heavy elements. However, there were discoveries of Gas Clouds that only contain Hydrogen and Deuterium. These primordial gas clouds are said to be remnants of the early universe.
What I Have Learned
The important concepts discussed in this module are:
- There are ways to estimate the distance and motion of celestial bodies. One way is using the Cosmic Distance Ladder, wherein a series of methods were used in succession to measuring distances of celestial objects.
- Doppler Effect (Red Shifting) in light allows scientists to determine that stars and galaxies are moving away from an observer. Doppler Effect together with Hubble’s discoveries was used to introduce the concept of an expanding universe.
- The existence of Cosmic Background Radiation, the proportion of Primordial Elements, the existence of primordial gas clouds, and observational evidence of the structure of recently formed galaxies served as evidence for the Expansion of the Universe from the extremely dense and hot state before the Big Bang. This proved that the universe expanded approximately 14 billion years ago.
What I Can Do
Time traveling is one of the most essential concepts in Science. One cannot travel back in the time given the present innovations and discoveries. According to this line, You can look back in time every time you look at the stars, do you agree with this? Explain your answer.
[transcriber’s note: blank answer box]
It is common knowledge that the universe is expanding. What do you think will be the future of our universe? Do you think there will come a time wherein we will have a more detailed understanding of the known universe?
[transcriber’s note: blank answer box]
Assessment
DIRECTIONS: Read each question carefully. Choose the letter of the best answer. Write your answer on a separate sheet of paper.
What is a light-year?
- A. The distance travelled by light in one year (365 ¼ days)
- B. The distance travelled by light in a leap year (366 years)
- C. The time required for light to cover 1 AU of distance travelled
- D. The time required for light to make a round trip from a nearby star
What is the approximate age of the universe?
- A. 14 million years
- B. 14 billion years
- C. 4.5 million years
- D. 4.5 billion years
What is an Astronomical Unit (AU)?
- A. It is the average spacing of the planets.
- B. It is the average distance of the earth from the Sun.
- C. It is the average distance of the earth from the moon.
- D. It is the average distance of the Sun from the nearest Star.
What is a parallax?
- A. An imaginary parallel line of reference when viewing distant stars.
- B. A unit of measurement of the displacement of celestial objects due to atmospheric factors.
- C. An apparent displacement of the observed position of objects viewed from different lines of sight.
- D. A pulsing of light emitted by stars that are at least 1200 Light-years away from the Solar System.
Which part of the spectrum does the Starlight show a shift in wavelength?
- A. Infrared end of the EM Spectrum
- B. Red light end of the visible spectrum
- C. Blue light end of the visible spectrum
- D. Ultraviolet-ray end of the EM spectrum
Which is TRUE about the movement of galaxies observed from earth?
- A. Far galaxies tend to move faster towards observers on earth.
- B. Far galaxies tend to move slower towards observers on earth.
- C. Far galaxies tend to move faster away from observers on earth.
- D. Far galaxies tend to move slower away from observers on earth.
What do red shifted lights mean?
- E. The source is slowing down.
- F. The source is moving towards the observer.
- G. The source is moving away from the observer.
- H. The source is moving perpendicular to the observer.
What does the redshifted light from a distant galaxy tell about the universe?
- E. It indicates that the universe is shrinking.
- F. It indicates that the universe is expanding.
- G. It indicates that the universe is not shrinking nor expanding.
- H. It indicates that the universe is shrinking and expanding in cycles.
The diagram on the right shows the comparison between the standard spectrum of an element and a spectrum produced by a distant star. What conclusion can be drawn from this?
- A. The distant star collapsed.
- B. The distant star is approaching the earth.
- C. The distant star is moving away from the earth.
- D. The distant star is following an elliptical movement.
[chart: comparison of spectra; “Standard Spectrum” and “Spectrum from Distant Star”]
Both spectra are labeled with: Ultraviolet (left end), Visible light (center arrow), Infrared (right end), and “Spectral lines” (marked above the lines).
- The figure below shows the spectral lines from an element in a laboratory.
[chart: spectral lines of an element in a laboratory; labeled VIOLET (left) and RED (right)]
Which diagram best illustrates the spectral lines of this element when its light is observed from a distant star moving away from the earth?
- A. [chart: spectral lines; labeled VIOLET (left) and RED (right)]
- B. [chart: spectral lines; labeled VIOLET (left) and RED (right)]
- C. [chart: spectral lines; labeled VIOLET (left) and RED (right)]
- D. [chart: spectral lines; labeled VIOLET (left) and RED (right)]
Additional Activities
Directions: Make a personal radar chart based on your evaluation of this module.
[chart: radar chart; SAMPLE]
Labels printed on the sample chart:
- I am able to visualize how the stars and galaxies are moving farther apart
- I understood the idea of measuring distances and motion of Celestial Bodies
- I am able to explain how the Cosmic Distance Ladder be used in approximating Celestial object distance
- I understood the concept of Doppler Effect and how it applies to Astrometry
- I understood how the lines of evidences were used to determine that the universe is expanding
[chart: radar chart (blank template); five-axis pentagon with three concentric rings]
Labels printed on the blank chart:
- I am able to visualize how the stars and galaxies are moving farther apart
- I understood the idea of measuring distances and motion of Celestial Bodies
- I am able to explain how the Cosmic Distance Ladder be used in approximating Celestial object distance
- I understood the concept of Doppler Effect and how it applies to Astrometry
- I understood how the lines of evidences were used to determine that the universe is expanding
Answer Key
[transcriber’s note: the answer key is printed upside down; the three boxes are shown left to right as Assessment, What’s In, and What I Know]
Assessment
A 1. B 2. B 3. C 4. B 5. A 6. C 7. B 8. C 9. 10. B
What’s In
Equinox 1. Solstice 2. Ptolemy 3. Copernicus 4. Kepler 5.
What I Know
A 1. B 2. B 3. C 4. B 5. A 6. C 7. B 8. C 9. 10. B
References:
Bennett, J., Donahue, M., Schneider, N., & Voit, M. (2018). Essential Cosmic Perspective 8th Edition. New York: Pearson .
Fraknoi, A., Morrison, D., & Wolff, S. (2018). Astronomy. Houston, Texas: OpenStax.
Howard, S. (2011, January). Cosmic Distance Ladder. Journal. Washington Academy of Sciences, pp. 47-64.
Tao, T. (2010, October 10). The Cosmic Distance Ladder. Retrieved from terrytao.wordpress.com: https://terrytao.wordpress.com/2010/10/10/thecosmic-distance-ladder-ver-4-1/
Image Sources:
- https://images.app.goo.gl/NsDdEr4AQXKKEVgM7
- https://web.archive.org/web/20161024200642/http://www.panoramio.com/photo/87990544
For inquiries or feedback, please write or call:
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