Visions of the Universe ~ Four Centuries of Discovery Discovering the Universe supplemental materials
Discovering the Universe Table of Contents - Exhibit Overview... 3 Science Background... 4 Science Misconceptions... 6 Glossary... 8 Related Educational Resources... 9
Exhibit Overview In turning his telescope to the heavens in 1609, Galileo embarked upon a journey that would revolutionize science and culture alike, profoundly changing our view of our place in the universe. Our views of the universe, and how they have evolved over time, are portrayed in the images and text of the Visions of the Universe: Four Centuries of Discovery exhibit. In recognition of the International Year of Astronomy, this exhibit includes six twosided panels that feature key astronomical discoveries from the past 400 years. The exhibit also highlights the technological advancements that made these discoveries possible. Exhibit topics range from celestial objects within our own cosmic backyard to those beyond the realm of our solar system. Featured objects include the Sun, the Moon, Saturn, Mars, comets, stars, nebulae, and galaxies. Images are accompanied by captions that highlight relevant, historical discoveries. The Visions of the Universe: Four Centuries of Discovery exhibit is supported by supplemental resource documents available online, in PDF format, for each panel. These twelve documents include science background information in the form of Q&As, related science misconceptions, a glossary, and links to additional resources on NASA s Amazing Space Web site. In addition, each exhibit panel is available as a downloadable, poster-size file. These materials are available from: http://amazing-space.stsci.edu/visions The Visions of the Universe: Four Centuries of Discovery exhibit was produced in December 2008 by the Space Telescope Science Institute, the American Library Association, and the Smithsonian Astrophysical Observatory, through funding from the National Aeronautics and Space Administration. 3
Science Background Q1: Why did it take so long for the Copernican model to be accepted? Nicolaus Copernicus (1473 1543) was the first astronomer to produce a scientifically based Sun-centered explanation for the motions of the objects in the sky. Copernicus lifetime work was recorded in a book called De revolutionibus, published in the year of his death. The book caused a mild controversy, but was not condemned by the Catholic Church. Six decades later, when Galileo began providing supporting evidence for the Copernican model through telescopic observations, the Catholic Church took official action against the book. The idea that the Earth moved around the Sun was contrary to the traditional view of an Earth-centered world. The work of Tycho Brahe and Johannes Kepler provided further evidence in support of the Copernican model. Isaac Newton s theory of gravity provided the scientific basis for the Copernican model over a hundred years after Copernicus work was published. Q2: How did the work of Tycho Brahe and Johannes Kepler contribute to our understanding of the motion of planets? Tycho Brahe (1546 1601), an observational astronomer, built precision astronomical instruments and made accurate observations before the invention of the telescope. He also changed observational practices by observing and recording the positions of the planets on a daily basis, as opposed to just when they were as close or as far as they could get. Brahe attempted to provide observational evidence refuting the Copernican model. Shortly before his death, he hired a young mathematician to help him understand his observations of Mars. Ironically, Brahe s accurate observations allowed his student, Johannes Kepler (1571 1630), to fit the observations to an elliptical orbit and derive the laws of planetary motion in support of the Copernican model. Q3: What are the Laws of Planetary Motion? The three Laws of Planetary Motion describe how the planets orbit the Sun. The first law describes the orbits as ellipses with the Sun at one focus. The second law describes how a planet moves within its orbit: slower when it is more distant from the Sun and faster when it is closer to the Sun. The third law compares the motions of one planet to another in a mathematical relationship. It basically calls for the planets closer to the Sun to move faster than more distant planets. Q4: Who were William and Caroline Herschel and how did they count stars to make a map of the Milky Way Galaxy? Continued 4
Science Background, continued William (1738 1822) and Caroline (1750 1848) Herschel were a brother-and-sister team of astronomers. A musician by training, William became obsessed with observing the sky and was forced to make his own telescopes because the ones available were not large enough to suit him. William would make the observation and Caroline would record it. William created a map of the Milky Way by making several assumptions about stars and the universe. The first assumption is that all stars are equally bright (an incorrect assumption). So a faint star must be more distant than a bright star. Hershel also assumed that stars are evenly distributed throughout space (also an incorrect assumption). By counting the number of stars visible in a small area of the sky, Hershel deduced the extent of the Milky Way in that direction. By repeating this count along 683 lines of sight, Hershel created a map of the Milky Way with the solar system near the middle of the map. Q5: What are variable stars and how did Edwin Hubble use them to calculate distance? Variable stars often called Cepheid stars are special because their variability or how fast they change from bright to faint and faint to bright depends on their true brightness. By measuring how fast the star changes in brightness, Edwin Hubble (1889 1953) calculated the star s true brightness. Then Hubble looked at how bright the star appeared to him. The farther away a star is, the less bright it appears. This is a well-known mathematical relationship that allows astronomers to determine distance when the true brightness and the apparent brightness of stars are both known. These stars allowed Hubble to show that the distance to M31, the Andromeda Nebula, was greater than even Shapley s proposed extent of our Milky Way Galaxy. M31 therefore was a separate galaxy much like our own. Q6: What is the cosmic web of galaxies and how were they mapped? The cosmic web of galaxies is the organization of galaxies into web-like structures across vast distances of the universe. Astronomers map the large-scale distribution of galaxies by measuring the distances to thousands of galaxies and plotting them in three dimensions. The galaxies are not randomly distributed, but instead lie upon intersecting lines that form a web-like appearance. Q7: What is the Hubble Ultra Deep Field and how was it created? The Hubble Ultra Deep Field (HUDF) is the deepest-ever visible-light view of the universe. Taken in 2004, the HUDF was preceded by the Hubble Deep Field-North, taken in 1995, and the Hubble Deep Field-South, taken in 1998. The visible-light image was taken by Hubble s Advanced Camera for Surveys (ACS). The ACS s wide-field camera took 800 exposures over four months, from September 24, 2003, to January 16, 2004. This amounted to about a million seconds or 11.3 days of viewing time. The HUDF field contains an estimated 10,000 galaxies. In ground-based images, the patch of sky in which the galaxies reside (just one-tenth the diameter of the full Moon) is largely empty. Located in the constellation Fornax, the region is below the constellation Orion. 5
Science Misconceptions MYTH 1: Gravity exists only on Earth. FACT: Gravity also affects objects in space. In fact, objects stay in orbit because of gravity. Without gravity, a satellite launched from the Earth would simply drift off endlessly into space, traveling in a straight line, instead of circling the planet. Gravity pulls objects toward the center of the planet, causing them to accelerate and drop toward the planet. MYTH 2: An object that appears faint in the sky is actually faint, and an object that appears bright in the sky is actually bright. FACT: The brightness of an object depends on its true brightness and its distance from Earth. Faint objects can appear bright if they are nearby, while bright objects may appear faint if they are very distant. MYTH 3: The Milky Way is only a band of light seen in the night sky. FACT: The Milky Way Galaxy is more than just a band of light. It contains countless stars and other matter. The Milky Way Galaxy is home to our solar system. MYTH 4: Most galaxies are easily viewed with the naked eye. FACT: Most galaxies are so far away that people can view them only with the help of telescopes. Only three galaxies can be seen with the unaided eye: the Andromeda Galaxy and the Large and Small Magellanic Clouds. These galaxies appear as cloudy patches in the sky. Other galaxies appear as fuzzy spots in the sky when viewed with small telescopes. MYTH 5: All galaxies are the same. FACT: The shapes of galaxies vary some are elliptical, others are spiral, and still others have no definite shape. Galaxies differ in color, composition, orientation, age, size, the number of stars within them, and their distance from Earth. 6 Continued
Science Misconceptions, continued MYTH 6: Galaxies are static, remaining unchanged with time. FACT: In fact, galaxies are dynamic and change over millions of years. Stars are born and die in galaxies. A galaxy also can interact with another galaxy, which alters both galaxies shapes. MYTH 7: You can judge the distance of a galaxy based on its size. FACT: The size a galaxy appears to be to an observer depends on how many stars are in it and how far away it is. Two galaxies may appear to be the same size. One of them, however, may be a small galaxy close to Earth and the other, a large galaxy that is much farther away. 7
Glossary Andromeda Galaxy A spiral galaxy approximately 2.5 million light-years away in the constellation Andromeda. It is the nearest spiral galaxy to our own, the Milky Way. It is also known as Messier 31, M31, or NGC 224. Copernican model The view of the universe put forth by Copernicus that was contrary to the prevailing belief that Earth was the center of the universe. Copernicus thought the planets orbited the Sun and the Moon orbited Earth. Copernicus also thought the Sun, in the center of the universe, did not move, nor did the stars move. Copernicus was correct about some things, but wrong about others. The planets travel around the Sun, but the Sun is not in the center of the universe. Cosmic web The pattern of galaxies observed on large scales of the universe that resembles a web. Ellipse A special kind of elongated circle. The orbits of the solar system planets form ellipses. Unlike a circle with one center, an ellipse has two points called focii (focus is the singular) that determine its shape. A circle is just a special case of an ellipse. Laws of planetary motion Three laws, derived by 17th-century German astronomer Johannes Kepler, that describe planetary motion. Milky Way Galaxy The Milky Way, a spiral galaxy, is the home of Earth. The Milky Way contains more than 100 billion stars and has a diameter of about 100,000 light-years. Model A representation of some aspect of nature that can be used to explain and predict real phenomena without involving myth, magic, or the supernatural. Variable stars A star whose luminosity (brightness) changes with time. 8
Related Educational Resources from NASA's Amazing Space Web site http://amazing-space.stsci.edu Amazing Space uses the Hubble Space Telescope s discoveries to inspire and educate about the wonders of our universe. The Amazing Space Web site includes curriculum support tools, a section for the general public, and a special section for educators and developers. The curriculum support tools are developed by a team of scientists, education specialists, and multimedia experts. They are aligned with national educational standards and are reviewed for scientific accuracy. Find teaching tools, graphic organizers, Online Explorations, and more. Online Explorations Online Explorations are fun, interactive activities for exploring various space science topics. Telescopes From the Ground Up Telescopes From the Ground Up traces the 400 years of telescope development from Galileo s refractor to NASA s Great Observatories. The overview for this activity can be found at: http://amazing-space.stsci.edu/eds/overviews/explorations/telehistory.php Specific sections of Telescopes From the Ground Up related to this exhibit panel include: Views of the universe: Ptolemy vs. Copernicus, which compares Ptolemy s Earth-centered model to Copernicus s Sun-centered one. http://amazing-space.stsci.edu/resources/explorations/groundup/lesson/basics/g37/ The changing shape of the solar system, which describes how our views of the solar system have changed because of telescopic observations. http://amazing-space.stsci.edu/resources/explorations/groundup/lesson/basics/g42/ 1845 Discovery: Cloudy objects are really spirals, which describes how Lord Rosse used his largest telescope to discover the spiral pattern in some nebulae. http://amazing-space.stsci.edu/resources/explorations/groundup/lesson/scopes/rosse/discovery.php 1923 Discovery: Other galaxies exist, which describes Edwin Hubble s discovery that galaxies exist outside our Milky Way. http://amazing-space.stsci.edu/resources/explorations/groundup/lesson/scopes/mt_wilson/discovery.php Understanding the size of the universe, which describes how our view of the universe has changed because of Edwin Hubble s work. http://amazing-space.stsci.edu/resources/explorations/groundup/lesson/basics/g45/ Galaxy Hunter In this Online Exploration, conduct a statistical analysis of the statistics lesson galaxies in the Hubble Deep Fields. The overview for this activity can be found at: http://amazing-space.stsci.edu/eds/overviews/explorations/hunter.php 9 Continued
Educational Resources, continued Hubble Deep Field Academy In this Online Exploration, examine the galaxies in the Hubble Deep Field-North. The overview for this activity can be found at: http://amazing-space.stsci.edu/eds/overviews/explorations/hdf.php Reading Selections These selections are grade-appropriate readings based on Hubble press releases. Star Witness News stories are written for grades 5 8. Tales of stories are written for grades 9 12. Star Witness News The Hubble Space Telescope: Time Machine to the Galaxies, which describes the deepest visiblelight observations ever made of the early universe. http://amazing-space.stsci.edu/news/archive/2004/03/ Tales of Finding one of the brightest and youngest galaxies in the early universe, which explains how scientists found this interesting galaxy. http://amazing-space.stsci.edu/resources/tales/young_bright.php The Early Cosmos: Out of the Darkness, which explores the formation of stars in the early universe. http://amazing-space.stsci.edu/resources/tales/early_cosmos.php Lithographs These are Hubble Space Telescope images of celestial objects that include informational text and inquirybased classroom activities. The Hubble Ultra Deep Field This lithograph features the Hubble Ultra Deep Field, the deepest visible-light observations ever made of the early universe. http://amazing-space.stsci.edu/eds/overviews/print/lithos/hudf.php 10