Physical Science 8th grade (1).pdf

C if the distance from earth to the moon were doubled

Info icon This preview shows pages 342–345. Sign up to view the full content.

View Full Document Right Arrow Icon
c. If the distance from Earth to the moon were doubled, what would happen to the gravitational attraction between them? 5. Neptune’s mass is about 17 times greater than Earth’s mass. Would your weight be 17 times greater if you visited Neptune? 6. What is the relationship between a planet’s distance from the sun and its orbital speed? 7. The average distance from Earth to the sun is: a. 1 light year. b. 1 astronomical unit. c. 385,000 km 8. Why does the sun feel warmer during summer and colder during winter in the northern hemisphere?
Image of page 342

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Chapter 16 The Sun and Stars Stargazing is an awe-inspiring way to enjoy the night sky, but humans can learn only so much about stars from our position on Earth. The Hubble Space Telescope is a school-bus-size telescope that orbits Earth every 97 minutes at an altitude of 353 miles and a speed of about 17,500 miles per hour. The Hubble Space Telescope (HST) transmits images and data from space to computers on Earth. In fact, HST sends enough data back to Earth each week to fill 3,600 feet of books on a shelf. Scientists store the data on special disks. In January 2006, HST captured images of the Orion Nebula, a huge area where stars are being formed. HST’s detailed images revealed over 3,000 stars that were never seen before. Information from the Hubble will help scientists understand more about how stars form. In this chapter, you will learn all about the star of our solar system, the sun, and about the characteristics of other stars. 1. Why do stars shine? 2. What kinds of stars are there? 3. How are stars formed, and do any other stars have planets?
Image of page 343
336 U NIT 6 A STRONOMY Figure 16.1: One of several nuclear fusion reactions that release energy in the sun by combining hydrogen into helium. star - an enormous hot ball of gas held together by gravity which produces energy through nuclear fusion reactions in its core. nuclear fusion - reactions which combine light elements such as hydrogen into heavier elements such as helium, releasing energy. 16.1 The Sun and the Stars What are stars? Where did they come from? How long do they last? During most of the day, we see only one star, the sun, which is 150 million kilometers away. On a clear night, about 6,000 stars can be seen without a telescope. Ancient astronomers believed that the sun and the stars were different from each other. Today we know that the sun is just one star like all the others in the night sky. The others appear to be so dim because they are incredibly far away. The closest star to Earth is Alpha Centauri: 4.3 light years (41 trillion kilometers). That is 7,000 times farther away than Pluto. Why stars shine Nuclear fusion A star is essentially an enormous, hot ball of gas held together by gravity. Gravity squeezes the density of stars so tightly in the core that the electrons are stripped away and the bare nuclei of atoms almost touch each other. At this high density, nuclear fusion occurs, releasing tremendous amounts of energy. The nuclear fusion that powers the sun combines four hydrogen atoms to make helium, converting two protons to neutrons in the process (Figure 16.1). The
Image of page 344

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 345
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern