Section 2 Locating Astronomical Objects in the Night Sky Section 2 Locating Astronomical Objects in the Night Sky What Do You See? What Do You See? Learning Outcomes Think About It In this section, you will When you try to find your way to a new address, what tools or • Construct a model of the night sky methods do you use? Do you find some ways of locating new to understand how star maps work. places more useful to you than others? How do you think it • Describe the coordinate system used would be different to find your way to a new place in space? to locate objects in the sky. • How do astronomers locate objects in the sky? • Identify patterns in the organization and distribution of matter in the Record your ideas about this question in your Geo log. Include a universe. sketch that demonstrates your ideas. Be prepared to discuss your responses with your small group and the class. Investigate In this Investigate, you will be comparing and contrasting ways of finding places both on the surface of Earth and in space. 21 EarthComm EC_Natl_SE_C1.indd 21 7/11/11 12:13:06 PM Chapter 1 Astronomy Part A: Describing the Locations of On a globe, they form a series of circles Places on Earth that decrease in size toward the poles. 1. With your group, discuss ways for Latitude lines show locations north locating places on Earth. and south of the equator. Lines of longitude are imaginary lines that run a) List all the ways your from the North Pole to the South Pole. group identified. They show locations east and west b) Rank your list from the of the prime meridian. You will now most accurate to the least sketch latitude lines using a compass, accurate descriptions. protractor, and ruler. 2. Use a globe, an atlas, the Internet, or 8. Use a compass to draw a circle 15 cm other sources to find the most precise in diameter. location of your school as possible. 9. Draw a horizontal line through the a) Record the location of your school. center of the circle (a diameter). 3. Exchange your description with one 10. Identify the longitude and latitude from another group. coordinates for your school. a) How does the accuracy of the other a) Record the longitude and latitude group’s description compare to yours? coordinates for your school. 4. Identify the locations of two places on 11. Use a protractor to draw an angle that Earth that have physical and historical is equal to the latitude coordinate for importance. your school. Measure the angle along the a) Record each location on a separate horizontal line and from the center of the sheet of paper. Research and describe circle. Draw the angle from the center of in a few sentences the importance of the circle to the edge of the circle. the physical nature and history of each place. 5. Exchange your sheets of paper with those from another group so that your group has two new places. 6. Locate each new place on a map. a) Did you have any difficulties finding each place? b) What information helped you or could have helped you in finding the places on the map? 7. You most likely used longitude and 12. Following the same procedure as in Step latitude coordinates to precisely locate 11, measure angles from 0° to 90° from the your school and the places of physical horizontal, and mark these on the circle. and historical importance on Earth’s surface. Lines of latitude are imaginary 13. Obtain a globe and a world map. lines on Earth’s surface that run east Examine the lines of latitude on the to west and parallel to the equator. globe and map. 22 EarthComm EC_Natl_SE_C1.indd 22 7/11/11 12:13:07 PM Section 2 Locating Astronomical Objects in the Night Sky a) How do these lines compare to the 3. Now imagine that you put the glass ball lines that you drew on your circle? into a much larger opaque ball without any markings on it. Your model now b) Describe how lines of longitude are consists of two concentric spheres, measured in comparison to lines with the opaque sphere at a distance of latitude. from the glass sphere. In your Geo Part B: The Celestial Sphere log, sketch what a cross section of this 1. Imagine Earth expanding and becoming “sphere within a sphere” would look 10 times its normal diameter. like. Again, compare your sketch to those of others in your group. a) Could you use the longitude and latitude coordinate system from a) What pattern do you think would be Part A for this larger Earth? Explain projected onto the inside of the larger your answer. sphere by the light shining out from the glass ball? Sketch this pattern. 2. To create a coordinate system for locating objects in the sky, you first need b) How would this pattern be similar to to make an imaginary model of Earth. the one on the glass ball? Imagine Earth’s core as a glass ball c) How would this pattern be different with two poles and an equator, just like from the one on the glass ball? Earth’s. Think about this ball as having lines of longitude and latitude just d) How could you use coordinates like those on a globe. These longitude to find objects located on the and latitude lines are opaque, which larger sphere? means light cannot pass through them. Think of the glass between the lines as transparent, which means light can pass through it. Learning Through Technology a) In your Geo log, sketch what this To use online resources to glass ball might look like. Share it practice finding objects in with others in your group. space, go to the EarthComm b) If you put a light bulb in the center Web site at http://www of the glass ball that radiated light .agiweb.org/education/earthcomm2/. outward in all directions, and turned There you will be able to explore the ways out the lights in the room where the in which astronomers locate stars, planets, ball was, what would you see on the and other celestial objects. wall and ceiling? Discuss this with your group. 23 EarthComm EC_Natl_SE_C1.indd 23 7/11/11 12:13:07 PM Chapter 1 Astronomy Digging Deeper THE CELESTIAL SPHERE In the Investigate, you explored different ways of locating places on Earth. You then investigated how you could find objects in space. Locating objects in space has been a challenge for people for a very long time. For thousands of years, people from all parts of the planet recognized groups of stars in the night sky. The Greeks, Egyptians, Babylonians, and others gave names to the groups of stars. They told stories about them that allowed for their positions to be learned without needing instruments. Some scientists think that caves in France may contain drawings of the night sky from 17,300 years ago. Figure 1 An ancient star chart showing animals and objects that represent the constellations. Geo Words There are 88 groupings of stars in the sky. Astronomers call a grouping constellation: a of stars a constellation. Each constellation has a Latin name. The name is grouping of stars in given a three-letter abbreviation. For example, Cassiopeia is abbreviated the night sky that as Cas. Draco is abbreviated as Dra. Constellations are important reference forms a recognizable pattern. points for locating planets and other astronomical objects in the night sky. celestial sphere: an Many ancient astronomers thought that the stars were attached to a imaginary sphere giant hollow sphere that surrounded Earth. Astronomers now know of infinite radius that projects around that such a sphere does not exist. Stars are located throughout space at Earth, and whose different distances from Earth. However, the idea of a giant sphere, called interior is inscribed the celestial sphere, is useful. It provides a model on which to place and with a grid system locate stars, planets, and other objects in space. The word celestial means for taking celestial coordinates. pertaining to the sky. The difference between astronomical objects and celestial objects is that celestial objects do not include Earth. 24 EarthComm EC_Natl_SE_C1.indd 24 7/11/11 12:13:07 PM Section 2 Locating Astronomical Objects in the Night Sky Figure 2 View of the celestial sphere looking toward the north celestial pole. To describe the location of an object in the sky, astronomers use a special Geo Words reference system. It is known as the celestial coordinate system. This celestial coordinate system is similar to the one used for locating objects on Earth’s surface. It system: a coordinate system for mapping uses measurements from known reference points or lines. These lines are positions on the similar to lines of longitude and latitude. The main reference line in the celestial sphere. celestial sphere is the celestial equator. It is an imaginary circle created by longitude: an east- extending Earth’s equator into space. west measurement of position on Earth. latitude: a north- south measurement of position on Earth. celestial equator: an imaginary circle created by extending Earth’s equator into space; the main reference line in the celestial sphere. Figure 3 Locations on Earth’s surface can be precisely located using longitude and latitude. 25 EarthComm EC_Natl_SE_C1.indd 25 7/11/11 12:13:07 PM Chapter 1 Astronomy Geo Words declination (dec): a The celestial coordinate system uses declination (dec) to measure how far coordinate used on north or south an object is from the celestial equator.