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Earth Space Science : 08 Our Solar : 08.00 Our Pretest

Our Solar System Pretest Our solar system is our neighborhood within a vast . And just as in any city, we're not the only neighborhood around. The has many solar , just as the universe has many . Let's look at how our solar system got its start. The solar system was formed about four and a half billion years ago when a cloud of gases and became compacted. At the center a was born, the , which contains more than 99 percent of the solar system's . The dust that orbited the sun agglomerated to form , including , as well as millions of other celestial bodies such as and . The solar system has a total diameter of twelve billion kilometers.

Every solar system was brought together by the same force—. Gravity plays a tremendous role in the universe. Whether it is involved in forming and planets or influencing the structure and stability of solar systems, there is much to learn about the effects of gravity. With gravity and millions of years, particles of matter can come together in space. As gas molecules and dust particles move closer to one another, the gravitational pull between them increases. Little by little, the mass adds up and increases the rate at which matter assembles. It eventually groups into large gas and dust clouds called , which are birthplace for and their solar systems. Consider the anchoring phenomenon for this module: Gravity is a pivotal force in the birth, development, motion, and interactions of objects within our solar system.

It is also this same force of gravity that caused a lot of chaotic bombardment in the early formation of the objects in the solar system. This module will focus on these driving questions:

• What models, theories, and tools have scientists used to understand our solar system and its formation? • How have forces played a role in the development of our solar system, and how do they allow us to represent and predict planetary motion? • What are the properties of the objects in our solar system, and how do those properties help us understand the age and formation of objects in the solar system? • How do Earth, the sun, and the interact to form a system that creates observable phenomena?

Earth Space Science : 08 Our Solar System : 08.01 Formation of Our Solar System Objectives

How have ideas about our solar system changed over time? At the end of this lesson, you will be able to:

• explain the formation of the in our solar system • explain how the work of scientists has shaped our views of the solar system • compare models of our solar system over time • identify different methods of measuring astronomical distances and apply them in various scenarios

Gazing into the night sky, ancient people explained astronomical events in terms of religion and philosophy. With the European Renaissance, scientific and religious explanations for astronomical events diverged. As the distinctions between science and religion became clearer, scientists increasingly used scientific instruments to make astronomical observations. Imagine you could travel backward in time and talk to scientists from the past. The scientists would tell you about two different models of the solar system. Use the activity below to place a “call” to two important scientists from the past:

Call between Ptolemy and Copernicus

Sound of dialing followed by ringing followed by a phone being answered

Ptolemy: Hello, this is Claudius Ptolemy. Student: Hello. I’m a student in an Earth space science class in the 21st century. Can you tell me what you think about and our solar system?

Ptolemy: Oh, yes, I have lots of ideas about the solar system. I even wrote books about the topic.

Student: Really? Where does Earth fit into the solar system?

Ptolemy: Why, that’s an easy one! Earth is the center. When you look at the sky at night, you can see all the stars moving around Earth. Therefore, Earth is at the center.

Student: Thank you. I have another call to make. It was nice talking to you.

Sound of phone being hung up, followed by new dialing, ringing, and another phone being answered

Student: Hello, may I speak to ?

Copernicus: This is he. What can I do for you? Student: I understand you lived during the scientific revolution that happened during ’s Renaissance. Can you tell me anything about the within the solar system?

Copernicus: Indeed, I can. I have taken many observations and I have concluded that the sun is the center of the solar system. Student: Really? I heard differently?

Copernicus: Well, sometimes science builds on both the accomplishments and mistakes of the past. I am convinced my model is the correct view of the solar system.

Student: Thank you. I appreciate your time. Sound of phone being hung up

Our Solar System

In 1977, NASA launched two unmanned space probes, Voyager 1 and Voyager 2, to explore our solar system and beyond.

Answer: The probes have been travelling for more than 30 years, and they still have not reached the very outer limits of the solar system, as most scientists define it. However, the probes did pass the outermost planets in 1989.

Solar System:

The Sun: The sun is the star in our solar system that provides warmth and light to the planets.

The Planets: Planets are objects that a star. A is massive enough to have gravity of its own but not massive enough to ignite.

Moon: are objects that orbit planets. : One of the small objects in our solar system that orbit the sun.

Small Bodies: Many objects not big enough to be planets orbit the sun. These objects include comets, asteroids, and . Each will be described in more detail in a subsequent lesson in this module.

The Universe: The universe includes all galaxies, stars, dust, gases, planets, and space. Our solar system is a very tiny fraction of the size of the universe.

Distances In Space:

Distances in space can be measured using a variety of units. For large distances, a light year is often used. For distances within the solar system, the is often used. One AU equals 150 million kilometers, Earth's average distance from the sun. (Because the distance between Earth and the sun changes throughout the year, it is more appropriate to speak of Earth's average distance from the sun, which is approximately 149,597,871 kilometers. For simplicity's sake, this number is rounded up to 150 million kilometers, or 93 million miles). The solar system does not simply stop at a certain point. It's a bit like a city, where the edges are hard to define. Because the outer boundary of the solar system is not clearly defined, it's difficult to say how big the solar system is. Its size can be measured from a region beyond 's orbit where the sun's influence greatly decreases and interstellar space begins. The region encompassed from the sun to this boundary is called the , as shown in the image below:

As you can see, the heliosphere is very large. The solar system occupies only a small part of the heliosphere. Let's estimate the size of the solar system by imagining the sun on a scale you can easily visualize. The sun is approximately 1.4 million kilometers in diameter. To create our scale model of the solar system, think about the sun as being the size of a basketball (78 centimeters in diameter). Using this scale, Earth's diameter would be only 7 millimeters. Using this same scale, the distance to Pluto would be about 3,300 meters. If a basketball on your desk represented the sun, then by the same scale you would have to walk more than 2 miles to reach Pluto!

Calculating of AU:

How many kilometers are represented by 155 AU? To calculate the answer, complete the following activity:

Calculation of AU Step 1 1 AU = 150,000,000 km This is the conversion factor used to determine the answer. This is a known value. Calculation of AU Step 2 155 AU = x km To calculate the number of kilometers in 155 AU, set up the following equation. The unknown portion of the equation is the number of kilometers. Calculation of AU Step 3 155 AU

150,000,000 km /1AU = x km Now use the conversion factor to convert AU to kilometers. Because 1 AU is equal to 150 million kilometers, that ratio can be substituted into the equation. Calculation of AU Step 4 155 AU

150,000,000 km /1AU = 23,250,000,000 km Multiplying the number of AU by the conversion factor gives the correct answer.

Practice This One On Your Own:

How many AU are represented by 480 million kilometers?

The History of Solar System Models Claudius Ptolemy: Ptolemy wrote a book that contained the key astronomical ideas of the time. From about 150 AD, his model dominated scientific thought. He thought the solar system was geocentric—the planets and sun travel around Earth in “epicycles,” or large perfectly circular . His model is also known as the Ptolemaic view of the solar system. Prior to Ptolemy, other ancient philosophers, such as Aristotle, also suggested the universe was geocentric, but Ptolemy was the first to explain this model in detail. Nicolaus Copernicus: Copernicus is considered the father of modern astronomy. Born in 1543, he used scientific measurements of the planets and stars. He published a book with the then-controversial idea that Earth was not at the center of the universe. He provided data and evidence to show that the solar system was heliocentric. This idea was not very popular in his day because it challenged the Ptolemaic view which had become the Roman Catholic Church’s official explanation. To the church, Copernicus’s idea that Earth was not at the center of the universe was antireligious heresy. Tycho Brahe: Brahe built one of the first scientific observatories designed solely to study the sky. He was a diligent note taker and made many calculated observations of the movement of objects in the universe. He is known as the “man with the golden nose” because he lost the tip of his nose during a duel and had a brass and nose replacement. : Brahe hired Kepler as an assistant in the late 16th century. After Brahe’s death, Kepler used the meticulous notes and data gathered by Brahe to make discoveries about the motion of the planets. Kepler’s work proved Copernicus’s view that the solar system was heliocentric. Kepler also introduced the word “satellite” and became the first person to suggest the sun rotates. : Galileo was the first person to scientifically observe rotation of celestial objects. He constructed one of the earliest telescopes and was the first to use a telescope to study the night sky. He identified several of ’s moons by studying the planet. This led him to suggest that it was like a solar system in miniature with Jupiter at the center. The church rejected Galileo’s views and threatened him with death. Sir : Newton was a mathematician and philosopher credited with many discoveries. He was the first to describe gravity and how the planets moved as a result of gravitational forces. He invented the reflecting telescope, which today is the main type of telescope used by astronomers. He also discovered that white light is made up of all colors, enabling astronomers to better understand the composition of stars.

Today, the heliocentric model of the solar system is universally accepted. Human and robotic exploration of the solar system have given scientists a more detailed and accurate view of the solar system and the universe.

Rotation and Revolution of the Planets Interactive

According to this diagram of the solar system: The sun’s radius is 700,000 km and its mass is 333,000 times Earth’s mass. is 0.39 AU from the sun. The planet’s radius is 2,439 km, and its mass is 0.055 times Earth’s mass. Its revolution rate is 88 days, and its rotation rate is 58.7 days. Mercury has zero satellites. is 0.72 AU from the sun. The planet’s radius is 6,051 km, and its mass is 0.81 times Earth’s mass. Its revolution rate is 225 days, and its rotation rate is 243 days. Venus has zero satellites. Earth is 1 AU from the sun. The planet’s radius is 6,378 km. Its revolution rate is 365.26 days, and its rotation rate is 23 hours and 56 minutes. Earth has one satellite. is 1.52 AU from the sun. The planet’s radius is 3,393 km, and its mass is 0.11 times Earth’s mass. Its revolution rate is 687 days, and its rotation rate is 24.6 hours. Mars has two satellites. The belt that divides the inner planets from the outer planets ranges from 2.5 to 3.5 AU from the sun. A typical asteroid’s mass is 0.0003 times Earth’s mass, and its revolution rate is 4.5 years. Jupiter is 5.2 AU from the sun. The planet’s radius is 71,492 km, and its mass is 318 times Earth’s mass. Its revolution rate is 11.9 years, and its rotation rate is 9.8 hours. Jupiter has 16 satellites. is 9.54 AU from the sun. The planet’s radius is 60,268 km, and its mass is 95.2 times Earth’s mass. Its revolution rate is 29.5 years, and its rotation rate is 10.2 hours. Saturn has 18 satellites. is 19.2 AU from the sun. The planet’s radius is 25,559 km, and its mass is 15 times Earth’s mass. Its revolution rate is 84 years, and its rotation rate is 17.2 hours. Uranus has 15 satellites. is 30 AU from the sun. The planet’s radius is 24,764 km, and its mass is 17.1 times Earth’s mass. Its revolution rate is 165 years, and its rotation rate is 19.2 hours. Neptune has eight satellites. Pluto ranges from 29 to 49 AU from the sun. The planet’s radius is 1,142 km, and its mass is 0.002 times Earth’s mass. Its revolution rate is 249 years, and its rotation rate is 6.4 days. Pluto has one satellite. Pluto is not a true planet; it is a . The consists of more than 1,000 KBOs, or Kuiper belt objects, that range from 30 to 100 AU from the sun. Kepler's Laws Interactive

Explanations of Kepler’s Three Laws of Planetary Motion: The Law of Ellipses: A circle is a shape with one center point, also known as the focus. An ellipse is an elongated or flattened circular shape with two center points, also known as foci (plural of focus). Kepler’s first law states that the sun is at the center of one of the solar system’s foci. There is nothing at the center of the other foci. The Law of Equal Area: Kepler’s second law states that the motion of the planets around the sun covers the same area in the same amount of time. Therefore, a planet moves fastest when it is closest to the sun; this increased speed allows it to cover the same area as when it is farthest from the sun. Earth moves on its orbital path at an average speed of 30 kilometers per second; it moves faster when it is closer to the sun and slower when it is farther from the sun. The Law of Periods: Kepler’s third law defines the time it takes a planet to complete one orbit around the sun. The relationship shows that the farther a planet is from the sun, the longer it will take to make one complete orbit. The time it takes a planet to make one orbit is called the period (P). According to the law, the square of the period (or P) equals the cube of the distance to the planet in AU (or A). For example, Mars completes one orbital period about every 1.85 Earth years. Mars’ average distance from the sun is about 1.5 AU (or 225 million kilometers). From these facts, P = 1.85 and A = 1.5. So Kepler’s third law is correct: 1.85 squared and 1.5 cubed both equal approximately 3.5. Scientists are still investigating the solar system, particularly its formation and structure. Over time, advances in technology and improved observation techniques have greatly advanced our knowledge of the solar system. Continued advances will improve our knowledge and enable us to continue exploring the solar system and beyond.

Exam: 08.01: Formation of Our Solar System

Which of the following scientists was a student of Tycho Brahe and gathered data that confirmed the heliocentric model of the solar system?

a. Galileo b. Kepler c. Newton d. Ptolemy

All the scientific theories used to explain the formation of the solar system are a. outdated b. imaginative c. non-testable d. unacceptable

Which of the following statements or expressions is most nearly associated with Kepler's Second Law of Planetary Motion? a. P2 = A3 b. Planetary orbits revolve around two foci. c. A planet moves fastest when it is farthest from the sun. d. A planet moves slowest when it is farthest from the sun.

At its closest point, Mercury is approximately 46 million kilometers from the sun. What is this distance in AU? a. 0.3 AU b. 2.4 AU c. 30 AU d. 150 million AU

Galileo and Newton both studied the night sky. Galileo studied Jupiter and its moons. Newton studied the gravitational force that held the planets in orbit. Which of these statements best explains why the two scientists proposed different theories about the solar system? a. Both had limited data. b. Both had different interests. c. They wanted to contradict each other's theory. d. They wanted to be the first to discover new planets.

In the history of astronomy, which of the following is true? a. Tycho Brahe built one of the first observatories. b. Ptolemy was criticized for his work on the heliocentric model. c. Nicolaus Copernicus could NOT prove that the sun was the center of the universe. d. Johannes Kepler argued that Earth was the center of the universe.

Saturn is 9.54 AU from the sun. What is its distance from the sun in kilometers? a. 14,000,000 km b. 15,723,270 km c. 57,000,000 km d. 1,431,000,000 km

Given the equation P2 = A3, what is the orbital period, in days, for the planet Venus? (Venus is located 0.72 AU from the sun?) a. 72 days b. 225 days c. 500 days d. 5,375 days