LDEO NGSS Summer Institutes: “Teaching about Astronomy” (GED 7214)
Lesson 5: Planetary Motion and the Major Planets of Our Solar System
Expect Time Required: 3 – 4 hr
Submitted by: Date: Time Needed:
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Selected NGSS Connections:
ESS1.A: The Universe and Its Stars
ESS1.B: Earth and the Solar System
- The solar system consists of the sun and a collection of objects, including planets, their moons, and asteroids that are held in orbit around the sun by its gravitational pull on them. (MS-ESS1-2),(MS-ESS1-3)
- This model of the solar system can explain eclipses of the sun and the moon. Earth’s spin axis is fixed in direction over the short-term but tilted relative to its orbit around the sun. The seasons are a result of that tilt and are caused by the differential intensity of sunlight on different areas of Earth across the year. (MS-ESS1-1)
- The solar system appears to have formed from a disk of dust and gas, drawn together by gravity. (MS-ESS1-2)
| MS-ESS1-2. | Develop and use a model to describe the role of gravity in the motions within galaxies and the solar system. [Clarification Statement: Emphasis for the model is on gravity as the force that holds together the solar system and Milky Way galaxy and controls orbital motions within them. Examples of models can be physical (such as the analogy of distance along a football field or computer visualizations of elliptical orbits) or conceptual (such as mathematical proportions relative to the size of familiar objects such as students’ school or state).] [Assessment Boundary: Assessment does not include Kepler’s Laws of orbital motion or the apparent retrograde motion of the planets as viewed from Earth.] |
| MS-ESS1-3. | Analyze and interpret data to determine scale properties of objects in the solar system. [Clarification Statement: Emphasis is on the analysis of data from Earth-based instruments, space-based telescopes, and spacecraft to determine similarities and differences among solar system objects. Examples of scale properties include the sizes of an object’s layers (such as crust and atmosphere), surface features (such as volcanoes), and orbital radius. Examples of data include statistical information, drawings and photographs, and models.] [Assessment Boundary: Assessment does not include recalling facts about properties of the planets and other solar system bodies.] |
| HS-ESS1-4. | Use mathematical or computational representations to predict the motion of orbiting objects in the solar system. [Clarification Statement: Emphasis is on Newtonian gravitational laws governing orbital motions, which apply to human-made satellites as well as planets and moons.] [Assessment Boundary: Mathematical representations for the gravitational attraction of bodies and Kepler’s Laws of orbital motions should not deal with more than two bodies, nor involve calculus.] |
Introduction
Understanding “Earth’s Place in Space” has been among the most significant advances in Human Knowledge. Only in the past few centuries have we come to recognize that Earth is not the center of the Universe, but only one of an unknown number of planets orbiting billions of stars in billions of galaxies. What makes Earth special is that we are the only known place with the ability to recognize this. There may be other forms of intelligent Life somewhere else, but to date we have not encountered any. So trying to understand what makes Earth and our Solar System unique deserves special consideration.
The Solar System
From Earth’s surface, people have been able to look into space and notice that certain objects behaved differently than the more numerous stars. These objects seemed to move across the sky and were given the name “planets” from the Greek word for “wanderer.” Ancient cultures thoughts these might be visible appearances of some of their gods, and we still attach names such as “Venus” and “Mars” to these objects.
Until the late 18th Century, everyone “knew” there were five planets accompanying the Sun and Moon. About the time the American Revolution was ending, William Herschel, an English astronomer, made an amazing discovery: he saw a new planet in his telescope, which was eventually named “Uranus” (pronounced “your’-a-nus.”) With this discovery, people realized that there was much about the Universe that we did not know. The past two centuries have produced an explosion of ideas that create our current view of our Solar System and the rest of the Universe. But we also recognize that new discoveries will be made and our knowledge will change.
At this point in time, most astronomers recognize that our Solar System consists of 8 planets—Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune—along with many “dwarf planets”—including Pluto—and other objects, including asteroids and comets.
The NASA “Solar System and Beyond” website provides some of the finest images and sources of information about the planets. “Facts and Figures” about each planet and selected other objects, including Earth’s Moon, provides valuable information that students can use to create presentations. One example of a class assignment is this “Planet Tourism Ad Campaign.”
Response: How might you incorporate this or similar student presentations into your classroom?
Planet Study in the Physical Setting/Earth Science (Regents Earth Science) Curriculum
The PS/ES Core Curriculum includes selected concepts about the Solar System that students are expected to know and the “Solar System Data” chart on page 15 of the PS/ES Reference Tables presents facts to know about these celestial objects. These will be the basis for what we do in this Lesson.
Focus 1: Planetary Motion
We will first examine the forces that produce planetary motion. As you can see from the Selected NGSS DCIs and PEs at the beginning of this Lesson, these are considered very important. The RES Core Curriculum further identifies key concepts, including:
1.1a Most objects in the solar system are in regular and predictable motion
> These motions explain such phenomena as the day, year, seasons, phases of the Moon, eclipses,
and tides.
> Gravity influences the motions of celestial objects. The force of gravity between two objects in the
Universe depends on their masses and the distance between them.
1.1b Nine planets move around the Sun in nearly circular orbits.
>The orbit of each planet is an ellipse with the Sun located at one of the foci.
Two important advances in our knowledge were made in the 17th Century. First, Johannes Kepler applied mathematical analyses to observations made by Tycho Brahe, and discovered basic facts about planetary motion. These are often called Kepler’s Laws, and have formed essential guidelines for plotting orbits of celestial objects and the satellites we have launched during the past 60 or so years.
Earlier astronomers, such as Ptolemy, believed that planets moved in perfect circles around the Sun, evidence of the perfection of God’s Creation. But Kepler recognized that Brahe’s observations about the planets and Moon could only be explained by elliptical orbits with the Sun as one of the focal points. Here is one video explaining Kepler’s Laws.
The “RES Solar System Data” chart lists orbit eccentricities. Students need to learn how to draw ellipses as part of the skills required for RES. Here is one video showing how to draw ellipses and calculate the eccentricity.
Here is another created by Tom Gazda (Ichabod Crane H.S., Valatie, NY).
Response: What materials do you need for a lab activity about drawing ellipses and calculating eccentricities?
What background knowledge and skills do students need to bring to this activity?
Later in the 17th Century, Isaac Newton identified “Gravity” as the key force holding together all objects in the Universe. There is much that students should know about gravity, but here we will focus on how it explains orbital motion.
The Force of Gravity depends on two basic factors: the mases of the objects involved and the distance between them. This can be mathematically represented as:
F α (m1 m2) / d2
This means that the Force of gravity (F) depends on or is related to (α) the product of the two masses divided by the square of the distance between them. The larger the mass, the greater the pull of gravity. This is why the Sun is the most important object in our Solar System. As distance increases, the pull of gravity decreases.
Newton also identified three “Laws of Motion.” The first states that “An object in motion will remain in motion unless acted on by an outside force.” This means that once an object, such as a planet, is moving, it will continue to move. This is called “inertia.” (The opposite case—an object at rest—need not be considered here.)
Briefly, then, combining Kepler’s and Newton’s discoveries, we can explain that planets revolve in ellipitical orbits with the Sun at one focal point. There is nothing physical at the second focal point. “Perihelion” means the point in an orbit when the planet is closest to the Sun (“Helios”), and “Aphelion” refers to the point when it is furthest. Earth is at Perihelion about Jan 4 and Aphelion about Jul 3. The equivalent points for objects such as the Moon orbiting Earth are “Perigee” and “Apogee.”
{See the Word of pdf versions to view the image that belongs here.}
Astronomers have long studied the motion of planets and applied Kepler’s and Newton’s Laws to make predictions of the times that we would see celestial objects rise and set. The United States Naval Observatory, our nation’s Official Timekeepers, provides a resource to find these for major Solar System object and selected stars.
Response: Examine past RES exams. Select three Part A questions, three Part B questions, and three Part C questions that deal with this concept. Explain what students must do to answer correctly
Focus 2 : The Scale of the Solar System
We can see the Sun, Moon, and planets , and may wonder: “How far away from the Sun is Earth?” “How far away are the planets from Earth?” Astronomers have developed methods to estimate these distances, and the values are given in the ESRT “Solar System Data” chart.
Classroom Activity: “Making a Scale Solar System”
Another display created to demonstrate planetary and cosmic distances is the “Scales of the Universe” in the Rose Center for earth and Space Science at the AMNH. Examine the online resources to see what your students could learn there.
Incorporating Museum Displays In-Person or Online
Museums and science centers are among the best “teachers” of important concepts about Astronomy, especially planets. They have the expertise, technology, and financial resources to create displays which are viewed and instruct millions of people of all ages, every day!
If possible, visit the Rose Center for Earth and Space at the AMNH or space science displays at another institution.
Response: Write a brief outline of how you could incorporate these resources into your curriculum.
If it is not possible to make such a visit, or in addition, view the links below as examples of using online resources to enhance your curriculum.
Response: Explain how you could use these to expand your space science instruction.
AMNH Rose Center “Planets”
http://www.amnh.org/exhibitions/permanent-exhibitions/rose-center-for-earth-and-space/dorothy-and-lewis-b.-cullman-hall-of-the-universe/planets
Smithsonian Institution “Exploring Our Planets”
https://airandspace.si.edu/exhibitions/exploring-the-planets/online/
Basic Questions about Planets Students Should Be Able to Answer
1) What is a “planet”?
2) How do “terrestrial planets” different from the “Gas Giants”?
3) Which planet is smallest and closest to the Sun?
4) Which is the largest planet and has the most moons?
5) Which planet is almost the same size as Earth?
6) Which planets have rings?
7) Which is the “Red Planet”? Why does it have this nickname? How many moons does it have?
8) Which planet was accidentally discovered using a telescope?
9) Which planet was deliberately searched for based on observations of another planet and
application of Kepler’s and Newton’s Laws?
10) Which planet has only 1 natural satellite but thousands of artificial satellites?
{Submit your response as an attachment to michael@earth2class.org.}