1 - 1 9/2/09 ASTRONOMY 113Laboratory Celestial Rhythms: An Introduction to the Sky Introduction and Goals The sky is a beautiful and fascinating stage upon which celestial dances are performed nightly. The sky is also our window on the Universe; mankind's first cosmological inquiries were inspired by these motions of the heavens. Over the centuries we have become more and more disconnected from the sky, even as our understanding of the Universe becomes greater. The goal of this lab is to reintroduce you to the sky, and to develop in you a deeper knowledge of its arrangement and motions. Of course, this lab would best be done under the real night sky. Unfortunately we cannot guarantee clear skies in Madison, nor do we have the luxury of many years or the wherewithal to fly to distant lands. However, we do have the virtual reality of Voyager II, an electronic planetarium providing a rich array of observing opportunities. We encourage you to explore with Voyager beyond the instructions of the lab. Don't worry if you go off on an exploration and get "lost" - the TA can easily bring you back to any point in the lab. And you are encouraged to ask questions during the lab about anything you may find. Format The format of the text in this lab is designed to clearly distinguish different purposes: Text in normal font guides you through the lab. • Text in bold provides instructions for operating Voyager. Underlined text identifies key words or concepts to be learned.1 - 2 9/2/09 Text in italics is supplementary information for your pleasure. Q1: Questions in boxes must be answered in your lab book. Before You Come to Class ... Read the lab completely. Your time in the lab is best used observing the "sky", not reading this manual. Bring to class this lab manual, your lab book, a pencil or erasable pen, a straight edge, and a scientific calculator. Schedule This lab is designed to be completed in two lab sessions. You should be well into if not completed Section 4 in the first lab session.1 - 3 9/2/09 Section 1: Sunset It is dusk, and the Sun has just set. You are standing in a meadow, looking toward the northern horizon. Above you is the sky (no stars yet!) and below you is the ground. Curiously, there are letters on the horizon indicating which direction you are facing (north, south, east and west). You turn your head to look in different directions: • Move the horizontal scrollbar with the left and right arrows, or by dragging the scrollbar tab. (Note that when you grab the scrollbar tab, a compass appears to show the present direction.) You can also maneuver on the sky with the arrows on the keyboard. • Return to looking North. As the sky gets darker, more and more stars appear in the sky: • Turn on the stars. The button for the stars is among the small set of buttons near the lower left corner of the screen. • Go to Define Horizon in the Control menu. Click OK. Now you tilt your head back to look at the stars overhead: • Move the vertical scrollbar with the up and down arrows, and by grabbing the scroll bar. When you grab the scroll bar, an indicator appears to show the angle above the horizon at which you are looking. • Find the point in the sky marked "zenith." The zenith is the point directly overhead. Of course, you will never see it marked in the real night sky! • Lower your head (move the vertical scrollbar) so that the "North" is just above the bottom of the screen. Section 2: Figures in the Sky At first glance, the stars appear to be scattered at random in the sky. But it is the nature of humans to organize, and archeological records show that all civilizations have seen patterns in the stars, or constellations. The stars were thought to be in the realm of the gods, and often the constellations were linked to religion and myth. In Western cultures the constellations typically derive from Greek and Roman mythology, such as Aries, Leo, Andromeda, Orion, Hercules and Gemini. These patterns gave an organization to the sky that was essential for its study. Indeed, some people believe that many myths were made up for the sole purpose of remembering star patterns. Today, while few give any spiritual significance to the constellations, every culture still uses constellations to guide their way through the sky. Since the constellations are simply mnemonics, there is no "right" way to group stars. Different civilizations have created different sets of constellations from the same night sky. However, there are1 - 4 9/2/09 certain groupings of stars that are so distinctive that every civilization has grouped them together - although not always representing the same thing. One such group of stars is the one we call the Big Dipper, also seen as a Starry Plough in England, as a Wagon in Europe and Israel, and as the Government in ancient China! Find the Big Dipper in the Voyager sky. Once you have found it: • Turn on the constellation lines. The button for the constellations is among the small set of buttons near the lower left corner of the screen. • Turn on the constellation figures. Go to Constellation Figures in the Display menu. • Turn on the constellation labels. Display menu to Sky Labels to Constellations. The Big Dipper is actually the body and tail of Ursa Major, the Large Bear. • Use the scrollbars to wander around the sky. How many constellations do you recognize? In ancient times the 48 constellations catalogued by Ptolemy were widely accepted, but as astronomy became more precise (and as the skies of the southern hemisphere were included), many more constellations were added. There are now 88 constellations, as established by the International Astronomical Union in 1930. At that time boundaries were established for each constellation, so every star in the sky falls in exactly one constellation. If you wish to see them, turn on Constellation Boundaries (in the Display menu). Be sure to turn the boundaries off again! Section 3: Coordinates in the Sky Constellations are a reasonable system of organization for "naked eye" observations, but suppose that you wanted to direct someone to a faint comet that you just discovered in your telescope.