1. The streak of light in the photograph above was produced by a tiny particle from space burning up in Earth’s atmosphere. Shown to the left is Barringer Crater in Arizona.

2. Shown at left is the Arecibo telescope. Data collected with the telescope were used to make this model of the asteroid Toutatis. Magnet Word Diagram= Include: definition, example(s), picture, pronounce, origin, sentence, synonyms, fun facts. VOCABULARY orbit, solar system, galaxy, universe, constellation Before, you learned Earth is one of 8 planets that orbit the sun The Moon orbits Earth Earth turns on its axis every 24 hours Now, you will learn How the universe is arranged How stars form patterns in the sky How the motions of bodies in space appear from Earth

3. We see patterns in the universe. For most of history, people had very limited knowledge of space. They saw planets and stars as points of light in the night sky. However, they did not know how far those bodies were from Earth or from each other. Early observers made guesses about planets and stars on the basis of their appearance and the ways they seemed to move in the sky. Different peoples around the world connected the patterns they saw in the sky with stories about imaginary beings. We still have much to learn about the universe. Within the last few hundred years, however, new tools and scientific theories have greatly increased our knowledge. In this unit you will learn about the arrangement of planets and stars. You will also learn about the ways in which astronomers explore and study space.

5. Arrangement of the Universe If you look up at the sky on a clear night, you will see only a tiny fraction of the planets and stars that exist. The number of objects in the universe and the distances between them are greater than most people can imagine. Yet these objects are not spread around randomly. Gravity causes objects in space to be grouped together in different ways. The images show some basic structures in the universe. Like a camera lens zooming out, the images provide views of space at different levels of size. 1.Planets/Earth Our planet's diameter is about 13,000 kilometers (8000 mi). This is almost four times the diameter of the Moon, which orbits Earth. An orbit is the path of an object in space as it moves around another object because of gravity. 2.Solar System(s) Earth and eight other major planets orbit the Sun. The Sun, the planets, and various smaller bodies make up our solar system. The Sun is about 100 times greater in diameter than Earth. You could… Tip: The word orbit can be a noun or a verb.

6. fit more than 4000 bodies the size of the Sun between the Sun and the solar system's outermost planet at its average distance from the Sun. The Sun is one of countless stars in space. Astronomers have detected planets orbiting some of these other stars. 3.The Milky Way/Galaxies Our solar system and the stars you can see with your bare eyes are part of a galaxy called the Milky Way. A galaxy is a group of millions or billions of stars held together by their own gravity. If the solar system were the size of a penny, the Milky Way would stretch from Chicago to Dallas. Most stars in the Milky Way are so far away that our galaxy appears to us as a hazy band of light. 4.The Universe The universe is everything—space and all the matter and energy in it. The Milky Way is just one of many billions of galaxies in the universe. These galaxies extend in all directions. Astronomers study space at each of these different levels. Some focus on planets in the solar system. Other astronomers study distant galaxies. To learn how the universe formed, astronomers even study the smallest particles that make up all matter. What is the relationship between the solar system and the Milky Way? http://scaleofuniverse.com/Website:

8. Constellations If you want to find a particular place in the United States, it helps to know the name of the state it is in. Astronomers use a similar system to describe the locations of objects in the sky. They have divided the sky into 88 areas named for the constellations. A constellation is a group of stars that form a pattern in the sky. In the constellation Cygnus, for example, a group of bright stars form the shape of a flying swan. Any other objects in that area of the sky, such as galaxies, are said to be located in Cygnus, even if they are not parts of the swan pattern. The ancient Greeks named many of the constellations for animals and imaginary beings. Unlike the planets in the solar system, the stars in a constellation are usually not really close to each other. They seem to be grouped together when viewed from Earth. But as the illustration above shows, you would not see the same pattern in the stars if you viewed them from another angle. What relationship exists among the stars in a constellation? (Look at next slide;) Click Here and Observe the Night Sky - Animation Visualization:

10. The sky seems to turn as Earth rotates. You cannot see all of the constellations at once, because Earth blocks half of space from your view. However, you can see a parade of constellations each night as Earth rotates. As some constellations slowly come into view over the eastern horizon, others pass high in the sky above you, and still others set at the western horizon. Throughout the ages, many peoples have observed these changes and used them to help in navigation and measuring time. If you extended the North Pole into space, it would point almost exactly to a star called Polaris, or the North Star. If you were standing at the North Pole, Polaris would be directly over your head. As Earth rotates through the night, the stars close to Polaris seem to move in circles around it. Although not the brightest star in the sky, Polaris is fairly bright and easy to find. You can use Polaris to figure out direction and location. What causes constellations to change positions during the night?

11. The movements of planets and other nearby objects are visible from Earth. A jet plane travels at a greater speed and altitude than a bird. Yet if a bird and a plane flew overhead at the same time, you might think that the bird was faster. You would have this impression because the farther away a moving object is from you, the less it seems to move. Stars are always moving, but they are so far away that you cannot see their movements. Observers have seen the same constellation patterns for thousands of years. Only over a much longer period does the motion of stars gradually change constellation patterns. By contrast, the Moon moves across the star background a distance equal to its width every hour as it orbits Earth. The Moon is our closest neighbor. The planets are farther away, but you can see their gradual movements among the constellations over a period of weeks or months.

12. Planet comes from a Greek word that means "wanderer." Ancient Greek astronomers used this term because they noticed that planets move among the constellations. It is easiest to see the movements of Venus and Mars, the two planets closest to Earth. They change their positions in the sky from night to night. The apparent movement of the sky led early astronomers to believe that Earth was at the center of the universe. Later astronomers discovered that Earth and the other planets orbit the Sun. The timeline on pages 72–75 introduces some of the astronomers who helped discover how planets really move in the solar system. Ptolemy’s Geocentric Model Copernicus’ Heliocentric Model Galileo Galilei

13. The Cosmic Web of the Universe Superclusters = Small galaxy groups Voids

14. KEY CONCEPTS 1. What are the basic structures in which objects are grouped together in space? 2. What is a constellation? 3. How does Earth's rotation affect our view of stars? CRITICAL THINKING 4. Compare and Contrast How is the grouping of stars in a constellation different from the grouping of planets in the solar system? 5. Apply The planet Jupiter is farther than Mars from Earth. Which planet seems to move faster when viewed from Earth? Explain. CHALLENGE 6. Predict Suppose that you are standing at the North Pole on a dark night. If you keep turning clockwise at the same speed as Earth's rotation, how would your movement affect your view of the stars? (If…, then…, because...)