10_sk_sci9_se_ch10:Layout 1 3/28/11 8:14 AM Page 348 Stars are an important component 10 of galaxies. Outcomes What you will learn: • Early cultures and civilizations recorded observations of star life stages By the end of this chapter, and explanations of the universe. you will: • The formation and life cycles of stars, including the Sun, help us understand • examine how various cultures, past and present, the formation of not only the solar system, but galaxies as well. including First Nations and • Different types of stars are classified according to mass and life cycle. Métis, understand and represent astronomical • Galaxies have specific shapes and contain star clusters, black holes, and phenomena dark matter. • inquire into the motion and characteristics of astronomical bodies in our solar system and the universe • analyze scientific explanations of the formation and evolution of our solar system and the universe A collision between two spiral galaxies NGC 6050 and IC 1179 in the Hercules constellation Before Reading Key Terms Determining Importance • binary system • black hole • dark matter • galaxy When information seems far beyond your experiences, you must determine • magnitude • protostar its importance to you. Skim the bulleted items on this page and the next. • quasars • supernova Then, write two statements about how the solar system and the formation • universe of stars are important to you. 348 UNIT D ©P 10_sk_sci9_se_ch10:Layout 1 3/28/11 8:14 AM Page 349 Stars 10.1 Here is a summary of what you will learn in this section: • First Nations and Métis understandings explain the origins of the universe and astronomical phenomena such as the Milky Way and supernovas. • A star forms inside a nebula as gravitational forces pull dust and gas together, creating a spinning, contracting disk of material in which nuclear fusion Figure 10.1 This 14th century begins. Stars are classified illuminated manuscript shows according to their colour, an astronomer using a sighting luminosity, and temperature. tube, a precursor to the • Stars have life cycles during telescope, used to sight which they form and then Polaris to aid in telling time. evolve in one of three main ways. Looking Back in Time Every major culture has astronomers, people who investigate the universe and the objects in it. The universe refers to everything that physically exists—the entirety of space and time, and all forms of matter and energy. Long ago, astronomers had only three aids to help them understand the wonders of the universe: sharp eyesight, their current understanding, and an ability to make detailed observations (Figure 10.1). Today, highly powerful and sensitive instruments allow astronomers to peer farther and farther into the universe and to gather information about the celestial bodies and phenomena in it. Supercomputers can analyze the incoming data from 100 000 stars at the same time. When astronomers observe a faraway astronomical body, the distance they are looking across is so vast that they are really looking back in time. Light takes time to travel. When you look at your hand, for example, you see it not as it is, but as it was a few billionths of a second ago. At short distances, this delay is insignificant. However, when you are looking far into space, the delays begin to add up. For example, it takes about 1.5 s for the light from the Moon to reach Earth. Therefore, we always see the Moon as it was 1.5 s ago. The planet Jupiter, farther from Earth than the Moon is, appears to us as it did 45 min before. 10.1 Stars 349 ©P 10_sk_sci9_se_ch10:Layout 1 3/28/11 8:14 AM Page 350 All the thousands of distant twinkling stars we can see from Earth even without a telescope are part of the galaxy we live in, the Milky Way. A galaxy is a collection of hundreds of billions of stars that are held together by gravitational forces (Figure 10.2). The distance from the Milky Way to the other galaxies is extremely great. Scientists have also found that, with a few exceptions, all galaxies are moving farther away from ours and from each other. These are incredible thoughts, yet scientific evidence Figure 10.2 The Andromeda galaxy. In 3 billion years, our supports them and many other intriguing descendants will see a galaxy rise in addition to a sunrise conclusions about the nature of our universe. when Andromeda eventually collides with the Milky Way. D13 Quick Science A Map of the Universe The universe is so large that it can be difficult to know about). If you know the shape of each comprehend all the astronomical bodies and their object or a symbol to represent it, draw that. relationships to each other. A map can help you Do not concern yourself with trying to make visually show objects’ relationships to each other your map to scale. Label each object. and their relative positions in space. A Map of the Universe Purpose (not to scale) Earth Most Distant To list all the objects you know that exist in the from Earth universe and show their relationships to each other by arranging them on a map Figure 10.3 Step 2 Materials & Equipment 4. Post your map on a wall in the classroom. • poster paper or newsprint • felt pens Questions 5. Compare your map with that of other groups. Procedure How do they differ? How are they similar? 1. Working in pairs or a small group, brainstorm a list of all the different kinds of astronomical Pose New Questions bodies you know about. 6. What new objects did you learn about during this activity? 2. Copy the labels shown in Figure 10.3 onto the sheet of poster paper. 7. Compose a question about an object that is new to you, or one you find interesting, that you want 3. Arrange the objects from your list in the order to have answered by the end of this chapter. you might encounter them on a trip that begins at Earth and continues to the most distant 8. What challenges are there in using a piece of reaches of the universe (or as far out as you paper to map space? 350 UNIT D Exploring Our Universe ©P 10_sk_sci9_se_ch10:Layout 1 3/28/11 8:14 AM Page 351 More than a Ball of Plasma infoBIT Stars are hot balls of plasma that shine because nuclear reactions The Study of Stars are taking place at their core. When stars die, they explode and Astron is the Greek word for blow most or all of their matter into space. Some of that matter star, and the suffix -nomy means science or study. comes together in a way that makes a solar system. This means So, astronomy is literally that the atoms in every human being today came from earlier the study of the stars. stars that once existed in our part of the Milky Way. You are made of atoms that are very, very old. Elders also tell about the stars in the night sky. Some First Nations and Métis creation stories talk about human spirits coming from the stars, and when a human dies their spirit returns to the night sky as a new star. The idea that humans come from the stars is shared by many scientists and some Elders, although the details differ. Another First Nations and Métis idea is that we are all related to everything in Mother Earth. This idea has new meaning when we think about the scientific idea that our Earth and everything on it comes from the same earlier star in the Milky Way—we are all related to an early star by sharing the particles produced in that star. Measuring a Star’s Brightness It is easy to think that all the stars forming a constellation or infoBIT asterism lie at the same distance from Earth, as though drawn on Moon Magnitude a celestial sphere. In fact, the stars in a constellation vary greatly Earth’s Moon has a magnitude in their distances from Earth, with some being many times of Ϫ12.7 and our Sun has a Ϫ farther away than others. They only appear to be twinkling magnitude of 26.75. from a flat surface because they are of similar brightness. The brightness of a star is known as its magnitude. Some of the brightest stars in the night sky will have a magnitude of Ϫ1, and as the numbers get larger, the stars are less bright (Figure 10.4). A star with a magnitude of 0 will be brighter than a star with a magnitude of 1. This system was created by ancient Greek astronomers Hipparchus and Ptolemy. They divided the stars they could see into six magnitudes, but as technology changed, so did the divisions of magnitude. The Hubble Space Telescope can detect stars as faint as 30 magnitude! The use of magnitude allows astronomers to determine how far away a Figure 10.4 This time-lapse image shows supergiant Polaris, the star is and the current stage of its life cycle. North Star. It is more massive than the Sun and 1000 times brighter. 10.1 Stars 351 ©P 10_sk_sci9_se_ch10:Layout 1 3/28/11 8:14 AM Page 352 Other than our Sun, the nearest star to Earth is Proxima Centauri. It is part of a group of three stars that orbit each other, called the Centauri system (Figure 10.5), located about 4.3 ly away from our solar system. Although Proxima Centauri is the closest star to Earth after the Sun, it isn’t the brightest star we can see at night.