- ; Chapter 4 Naming ObjectS in TheSky Astronomers need to be able to assimilate and exchange information about specific objects in the sky. Many systems have been devised over the last few thousand years to identify and name the most conspicuous ones. As our technology has advanced, studies of astronomical objects have become more precise. Today it is common for astronomers to assign numerous designations to a single celestial body. Humans have observed the stars for millennia. Our ancestors named the bright stars as well as larger groups of stars called constellations. As we said in Chapter 1, the ancients named many of the constellations after mythological beasts, gods, demigods, and ordinary household objects. Astronomers continue to use the names of the constellations first recorded by ancient astronomers thousands of years ago. It is here that we may begin to learn about where things are located in the sky and how they are named. Astronomers officially recognize 88 distinct constellations today. TheSky displays all of them quite accurately. From the mid-northern latitudes, you can see over half of them. Most are visible every night from your location at some time during the night. TheSky helps you to find them but you must go outside on any clear night throughout the year and look for them yourself. About a half dozen or so constellations are visible every night from 40°north latitude all year round. These are the circumpolar constellations. They are all located in the northern sky near the North Star, Polaris. Using TheSky will definitely help you locate all these constellations easily during any season of the year. Exercise A is designed to help you locate some of the constellations visible from mid-northern latitudes. Exercise A: View Some Constellations I. Run TheSky. 2. Click Qata on the toolbar at the top of the sky window, then .s.iteInformation and then click the Location tab. 3. Set your location to 40° north latitude. The city or longitude is not important here! Figure 4-1 displays the appropriate information that should be entered into the Site Information window. 4. Click APply. -41- ~ 5. On the Qrientation toolbar, click "North" ~. 6. Go to View toolbar and click on the constellation lines.(I I),if they are not already displayed. 7. Click the common names button (~ on the View Toolbar, if they are not already displayed. 8. Go to the Time Skip toolbar and click the Go Forward. button and watch the motion. 9. List the names of the constellations that do not go below the northern horizon. These constellations are visible every night throughout the year and are known as circumpolar constellations. Exercise B is designed to find a particular constellation in TheSky. Exercise B: Find the Constellation of Orion I. Click gdit on the toolbar at the top of the sky window, and then Eind, or right click the mouse anywhere in the sky window. 2. Click on the "Constellation Labels" in the Common Names window. 3. Use the scroll bar and find the constellation Orion. Figure 4-2 displays the "Eind" window. -42- ~~.:'N;-~-{~('->j<~-t~ ' _:bL-~~'~ ?1~~~ .-. ~ .., . -- Planets. SI.I'I. Moon Comets Minor Planets Common Non-Stela! ".CommonStalN~I~ MessierO' . 4. Double-click on "Orion." 5. After clicking on "Orion," an Object Information window appears, like the one displayed in Figure 4-3. This box indicates where the constellation is located in the sky and other pertinent information about the constellation, such as the pronunciation of its name. ......... Figure 4-3 Object Information window. for Orion 6. Click the Rise, Transit, and Set button. at the bottom of the Object Information window. This displays the time of day that Orion appears to rise, cross your local celestial meridian, and set at your location. The time of meridian transit is the best time to view the object. At whattimedoesOrionappearto rise?_:_ At whattimedoesOrionappearto set? _:_ When is the best time to view Orion? _'_ 7. Next click the Center Object button (I~) at the lower left-hand corner of the Objec,t Information window. This will center Orion in your sky window. -43- 8. Click on some of the objects in the constellation. Did you find M42? 9. If a camera icon is displayed in the sky window, you can view an image of the object by simply clicking on the camera. If the camera icon is no! displayed in the sky window, then to view an image of the object you must click on the object. After clicking on the object, an Object Information window appears. Now click on the Multimedia tab to access any images of the object. You can display or hide the camera icons in your sky window by choosing either option in the Eilters menu. That's all there is to it. Try finding another constellation-perhaps one you like better than Orion. You can use this exercise to find any astronomical object in TheSky's database. Appendix B contains a list of the 88 recognized constellations. Now let's turn our attention to how astronomical objects are named or designated. Basically, astronomical objects fall into two groups, stellar and nonstellar. The first group includes only the stars. The second group has a more diversified population of astronomical objects. The later group contains objects that lie well beyond our Solar System. The nonstellar group contains objects such as nebulae, star clusters, and other galaxies. The planets in contrast are not included in either of these groups. Because they are Solar System objects, astronomers usually designate them by their given name. Let's first discuss how stars are designated. Over the millennia people have used several systems to denote the stars. The numerous cultures that have inhabited our planet have assigned many names to the stars over the years. Proper Names Astronomers usually refer to stars as either prominent stars or representative stars. Prominent stars are the bright stars. Stars, such as those displayed in Figure 4-4, are typically the bright stars seen in the winter months. They are located in the constellations of Taurus, Orion, Canis Major, and Canis Minor. The dot sizes displayed in the sky window, representing stars, indicate the stars' relative brightnesses, not their true physical sizes. In other words, the bigger the dot, the brighter the star; the smaller the dot, the fainter the star. The magnitude system that astronomers use in observational astronomv is discussed in ADDendixF. Figure 4-4 Prominent or bright stars of winter -44- l The bright stars of summer are typically those that are displayed in Figure 4-5. These stars are located in the constellations of Lyra, Cygnus, and Aquila. Figure 4-5 Prominent or bright stars of summer The brightest stars are usually designated with proper names. Only a few dozen stars are frequently referred to by their proper names. Several hundred stars have been named this way, but only a few are easily recognized by name. The bright stars are easily seen after the Sun goes down and twilight falls. The representative stars; in contrast, are those that are for the most part in the solar neighborhood. They are close by, so to speak. Their distances are within 4 to 8 parsecs of Earth. This is about 13 - 26 light years. Not many of the representative stars have proper names. The representative stars in the Milky Way Galaxy are usually fainter than the Sun's intrinsic brightness. These stars are usually small, cool, and very faint. On any clear night in spring, you can find the bright star Arcturus in the evening sky. In summer, it might be Antares (heart of the scorpion), or perhaps Vega, the brightest star in the constellation Lyra. In autumn, you might find the star Capella in Auriga, the charioteer. In the winter, it might be Betelgeuse or Rigel in the constellation of Orion. A list of some of the brightest stars is provided in Appendix A. This list includes the stars' designations, proper names, coordinates, apparent brightnesses, spectral types, intrinsic brightnesses, and their approximate distances. Exercises C and D are designed for you to locate some bright stars. Exercise C: Find the Bright Star Aldebaran Set your location for Cleveland, Ohio. Set the date for October 19,2005. Set the time to 9:00 P.M. Set Daylight Savings adjustment option to "North America." The Site Information window looks like that in Figure 4-6. -45- Figure 4-6 Site Infonnation window for Exercise C 1. In what constellation is Aldebaran located? 2. AtwhattimedoesAldebaranappeartorise?_:_ 3. AtwhattimedoesAldebaranappeartoset?_:_ 4. Whenis thebest timeto viewAldebaran?_:_ Exercise D: Find the Bright Star Altair Set your location for Golden, Colorado. Set the date for October 1, 2010. Set the time to 9:00 P.M. Set Daylight Savings adjustment option to "North America." 1. In what constellation is Altair located? 2. At whattimedoesAltairappearto rise?_:_ 3. At whattimedoesAltairappearto set? _:_ 4. Whenis the besttimeto viewAltair? _:_ Bayer Letters Because it is difficult for most of us to memorize the names of hundreds of stars, Johann Bayer developed a more convenient system in 1603. His system used Greek letters. The stars in the constellations in the northern sky were assigned letters according to their relative brightnesses. Bayer used the Greek alphabet to designate the stars by their order of brightness in each constellation. Each naked-eye star is labeled with a Greek letter followed by the genitive case (possessive--second person singular) of the Latin name of the constellation in which it is found. This system started with the brightest star in the constellation and went to the faintest.