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SIR WILLIAM HERSCHEL
SIR WILLIAM HERSCHEL
Germany (1738 - 1822)
Sir Frederick William Herschel was a German-born British astronomer and composer who became famous for discovering Uranus. He also discovered infrared radiation and made many other discoveries in astronomy.
 

He aquí una selección de 14 temas clave en el programa de televisión, que pueden coincidir con el tema de astronomía, el método científico, la tecnología y la ingeniería en la escuela o en la currícula universitaria. Para cada tema del show, listamos tópicos sugeridos para la discusión en clase o actividades que puedan ayudarlo a usted y a sus estudiantes a investigar más profundamente el tema.

(Haga click en cualquier tema para mostrar el contenido de la sección.)

  • Galileo was the father of telescope astronomy, of modern physics, and of the use of the scientific method. Students can find out more about Galileo's life and work by going to our Galileo Resource Guide. Then they can do one of the two activities on our web site under The Footsteps of Galileo to replicate some of the things Galileo did with his first telescope and what those experiments meant for humanity's view of itself in the cosmos.

    If at all possible, try to give each student a "Galileo experience" by allowing them to look through a telescope. Some colleges and science centers have small observatories which are open to the public (call local astronomy or physics departments to find out). But by far the best way to get a look through a telescope is to find an astronomy club near you. Many clubs hold "star parties" (evening observing sessions with telescopes) from time to time; some may even be willing to come out to your school and do an event there.

    If not, you may consider enlisting the help of parents in lending the class some binoculars; then wait until the Moon is visible in the morning and get students to look at the Moon through binoculars. They will be able to see the same roughness on the surface of the Moon that surprised Galileo. (It's perfectly safe to look at the Moon during the day with binoculars, but warn the students that pointing the binoculars toward the Sun is very dangerous, because intensified sunlight can really damage their eyes.)

    Today students grow up with the notion that the Earth is just another planet orbiting the Sun and this idea is reinforced in popular culture through cartoons, movies, toys, and more. But in Galileo's time, the notion that the Earth could be moving without our sensing it seemed the height of absurdity. If your students are older, you might assign them to research what the debate in the 1500's and 1600's was about and get them to stage a debate between believers in the geo-centric and helio-centric perspectives.

  • Many historians of science believe that progress in astronomy is mostly defined by improvements in our telescopes. Thus the history of astronomy can be viewed as the chronicle of advances in making telescopes. Check out our Introduction to Telescopes and the essay on Monster Telescopes and Future Telescopes on this site for background information.

    If you have a local amateur astronomy club in your area, you might ask one of their members to bring a large telescope to your class and show it to the students as you are studying optics, lenses, and mirrors.

    Discuss with the class the notion that telescopes are "light buckets" and that bigger buckets let you catch more light. Students could create a timeline of major telescopes and major discoveries in astronomy, side by side. Another interesting activity, if you have the kind of class that doesn't giggle too much in the dark, is to have students look at the size of the pupil in each other's eyes when the room is bright. Then darken the room and have them look at the size of their eye openings again. The darker it gets, the more your eye's pupil tries to open up and become a "bigger bucket" – to collect more light.

    If you have some lenses and other optical equipment in your school science store room, you may enjoy trying some of the hands-on activities in our Glass and Mirrors Toolkit.

    One of the biggest issues that astronomers face working on the surface of planet Earth is the increase in light pollution, the drowning of darkness by the lights of civilization, which all too often shine into the sky and not just on the ground where they are needed. Assign several students to research the issue of light pollution and give a report to the class. The International Dark-Sky Association, whose headquarters are in America's "astronomy capitol", Tucson, Arizona, provides a wealth of classroom material and general information on the topic of light pollution.

  • As discussed in the Introduction to Telescopes, the invention of photography helped astronomers in several ways. First of all, they now had a permanent record of what was in the sky – and one that did not depend upon human memory or pass through the human imagination before being set down. Second, long exposures allowed them to record scenes through a telescope that the eye alone could not see. (You can remind students that the eye collects light for a small fraction of a second, after which it sends the information to the brain for processing and then starts collecting all over again.)

    Since most students experience photography in their own families, you could have them make a list of all the ways photography has affected their lives. They might bring up the fact that they have a record of family and special occasions that they might otherwise not have. Or they might mention some clever effect like a snapshot of someone jumping off a big rock that makes the person appear frozen in the act of flying. Then they can brainstorm about the ways that the invention of photography would have changed the work of astronomers.

    Today, chemical photography has been overtaken by digital photography, both in most of our country's homes and in the work of astronomers. You might contrast for the students some of the ways in which digital photography has been an improvement. Digital cameras tend to be much more sensitive to light and can thus collect more light during a given amount of time. This again helps astronomers make dim things visible (and enables young people to record embarrassing scenes at family gatherings even when there is little light).

    In one of the many ways the U.S. is celebrating the International Year of Astronomy in 2009, NASA has sponsored a traveling exhibit called From the Earth to the Universe featuring some of the best astronomical photographs in large-print format. You can check with your local planetarium or science museum to see if the exhibit is coming to a place near you or visit our events calendar.

  • Students might begin by reading our Introduction to Telescopes if they have not done so already. Ask them to discuss what the greatest obstacles are to getting a clear view of the universe from the Earth's surface. You might lead them toward a discussion of human lights and how they make it difficult to detect the faint light from the universe. Also, mention the effects of the lower atmosphere — with its pollution, dust, smog, and clouds — in blocking the light, and how the motion of air makes images appear to twinkle and dance. Explain that astronomers building larger telescopes quickly realized that going to high mountaintops would the best solution to both of these obstacles.

    A simple way to simulate the effects of the Earth's turbulent atmosphere upon starlight is to use a hairdryer to blow a stream of hot, moving air into a flashlight's light beam.

    Students might also enjoy researching the trials and tribulations of Lord Rosse, an Irish nobleman who in the 19th century built several large telescopes on his estate in Ireland. The largest, a 72-inch (1.8-meter) reflecting telescope, was nicknamed the "Leviathan of Parsonstown." It was the largest telescope in the world from 1845 until 1917, but it was not usable on many nights of the year because of the Ireland's weather. His example became a major lesson for astronomers about where — and where not — to locate large telescopes.

    400 Years of the Telescope focuses in particular on Mauna Kea, a 14,000-ft high observatory on the big island of Hawaii, one of the optimal places on Earth for astronomy. The good news about setting up a telescope on Mauna Kea is that it is situated above nearly three miles of the Earth's atmosphere. At the same time, this elevation is bad news for astronomers: the air is thin and breathing is difficult. Suggest that your students read about the challenges of traveling at such altitudes and then discuss what it is like for the astronomers and technicians who work at the highest observatories on Earth.

  • Understanding the notion of the expanding universe can be very challenging, especially for younger students. This topic is often best left until high school or college, although many middle school students who read or watch television shows about astronomy get curious about it early.

    You can have students begin by reading our introductory essay, The Expanding Universe. A key idea, emphasized there and in the film, is that the Big Bang is not an explosion of material in a pre-existing space. Instead, it is an explosion of space, time, matter, and energy. When we observe the galaxies moving apart, it is because space itself continues to stretch. The notion of space somehow stretching and changing is a mind-boggling notion; you can assure students that scientists took a while to get used to it, as well.

    Engage your students in the little experiment that Alex Filippenko (the Berkeley astronomer) suggests in the show, stretching a rubber strap or band with small galaxy shapes attached to it and watching how the galaxies separate as you stretch the strap. Alternatively, glue some specks of glitter, or even small flakes of cereal, to a balloon, blow it up and observe how the specks separate as the balloon stretches. The farther apart two specks are, the more balloon there is between them to stretch, and the faster they will be seen to move apart. This relationship between distance and speed of separation is what astronomers call Hubble's Law.

    Students may also enjoy learning more about Edwin Hubble who had to defy his family to become an astronomer since his father did not think astronomy was a respectable profession. Your students might be amused to learn that Hubble spent some time as a high school teacher and coach before returning to graduate school and earning an astronomy degree. He also was a Rhodes scholar, studying in England in the same way President Bill Clinton did much later. An excellent book about Hubble's life is Edwin Hubble: Mariner of the Nebulae by Gale Christianson (1996, University of Chicago Press).

    One key idea to understanding the expanding universe is that astronomers, such as Hubble, needed to measure the speed at which galaxies were moving away from us. In fact, they used the same technique that highway police use to measure how fast motorists are driving. The technique involves the Doppler effect: the principle that waves given off by moving objects have a different frequency (or wavelength) than those from the same object at rest.

    As police bounce radar waves off of a speeding car, the shift in the waves' frequency determines the car's speed. Astronomers measure specific colors in the light of a distant star or galaxy and the change in those colors (the wavelength of the light) tells them how fast the object is moving toward us or away from us. You can simulate this by buying or constructing an inexpensive buzzer, tying a string to it securely and whirling it around your head. The frequency (pitch) of the sound waves will change when the buzzer is moving toward the students or away from them. (The same effect with sound, using a train, can be heard at the end of the very last cut on the Beach Boys' album Pet Sounds.)

  • Students might begin the study of modern telescopes and observatories by reading the two essays on our site, Introduction to Telescopes and Monster Telescopes, Future Telescopes.

    Since the film mentions a number of current or upcoming giant telescope projects, you might divide the class into several groups, ask each group to learn more about one project and then report to the class. If they can, have them report not only on the telescope(s), but also on the setting of the observatory, and what it is or will be like to work there.

    Some good recent articles on upcoming telescope projects can be found in these sources:

    Jedicke, Peter & Robert "The Coming Giant Sky Patrols" in Sky & Telescope, Sept. 2008, p. 30. About giant telescopes that survey the sky continuously.

    Lowe, Jonathan "Next Light: Tomorrow's Monster Telescopes" in Sky & Telescope, Apr. 2008, p. 20. About plans for extremely large telescopes on the ground.

    The major advances in spinning hot mirror material while forming it into a mirror mold — and making the mirrors honeycombed, instead of solid — were the result of pioneering work at the University of Arizona's Mirror Lab. Students are always amused to discover that this lab is adjacent to the University of Arizona football stadium which provided lots of room for making the biggest telescope mirrors in the world.

  • To assist students in understanding the key idea behind this section of 400 Years of the Telescope, it is important to show them that the typical telescope is designed to observe only a tiny area of the sky at a time. As a result, we don't have complete "coverage" of the sky at all times — instead, we sample small parts of it very deeply and thoroughly.

    Astronomers also take an occasional "census" of the sky, as they did between 1948 and 1958 from the Palomar Observatory or more recently in the more narrow, but deeper, Sloan Digital Sky Survey. But no survey from a single telescope can cover all of the Earth's sky. Consequently, these surveys are just one-time snapshots.

    This is very similar to what the U.S. Census Bureau does in making a survey of our population every ten years or so: it gives us a snapshot of the country at those intervals of time. In between the ten-year surveys, the Census Bureau takes much smaller, but deeper surveys, trying to answer specific questions about the American workforce, or of young people of a certain age, for example.

    The dream of many astronomers is to have regular coverage of the entire sky, almost like a movie, where we can repeatedly survey much of the universe and then compare how a portion of sky or a particular object appears over long periods of time.

    Students who have studied astronomy, or have looked further into the plans for the sky survey telescopes, might be asked to make a list of the kinds of things that astronomers hope to discover with such telescopes. What kinds of objects in the sky change their location or appearance with time?

    Students might also consider a survey of their own neighborhoods as an analogy. Suppose someone in an aircraft took an ongoing movie of their neighborhood, day after day, year after year. What things in their neighborhood change daily, weekly, monthly, and only over years? What would a movie of their neighborhood show — provided anyone had the patience to watch it in real time?

  • This topic can be a little frightening for younger children, and may be better left for the older students. In recent years, astronomers have begun to understand that asteroids (chunks of rock left over from the formation of our solar system) are not just collected in a belt between Mars and Jupiter. A number of them have orbits that carry them into the neighborhoods of other planets, including Earth. The ones that can come near the Earth are called NEO's (Near Earth Objects) or Earth-crossing Asteroids.

    Astronomers and geologists have accumulated evidence that many asteroids of various sizes have struck the Earth in the past. The Barringer Crater (about one mile across) is an impressive record of one such impact, and is a popular tourist attraction on the route toward the Grand Canyon in Arizona. A much smaller asteroid entered our atmosphere in June, 1908, exploding 4-5 miles up in the atmosphere above Siberia tundra in an area called Tunguska. The explosion devastated a region just about the size of Washington, DC. Fortunately there was no known loss of human life, but it remains sobering to think what might have happened had the asteroid exploded over a populated area.

    More and more evidence is accumulating that a large asteroid (perhaps 5 to 10 miles across) hit the Earth some 65 million years ago, lofting so much hot dust and smoke into the atmosphere that the climate of our entire planet changed. The dust-laden sky prevented significant amounts of sunlight from reaching Earth's surface, killing many plants and, soon afterward, the many animals that depended on them for food. The fossil record shows that large numbers of species were wiped out in this period, dinosaurs perhaps the most famous among them. In the 1990's the actual crater from this impact was discovered, buried under more recent geologic layers in Mexico's Yucatan region.

    Students may enjoy doing some book or Internet research on Comet Shoemaker-Levy 9, which, in 1993, broke into many pieces when it ventured too close to the giant planet Jupiter. The following summer, pieces of the comet came back around and collided with Jupiter; we could easily observe the enormous marks of these impacts from Earth. This display of cosmic danger was a wake-up call for governments and many people who had never thought about asteroids before; what had just happened to Jupiter could happen to the Earth. We know many smaller asteroids hit us regularly without damage, and still others pass close to us, most often with little or no warning. Surely, if a big one is headed our way, we want to have as much notice as possible.

    In 1998, under a mandate from Congress, NASA undertook Project Safeguard to find and track 90% of the Earth-crossing asteroids that were 1-kilometer or larger. We are now almost at the 80% level and closing in on this goal. In the meantime, a search for smaller asteroids that might someday hit us (and still be dangerous, even if they don't cause global devastation) is also under way. This search is what the Pan-STARRS telescope, introduced in 400 Years of the Telescope, is especially well-suited to carry out.

    After students complete a unit on asteroids and impacts, you may want to lead some class discussion on their thoughts and concerns. Reassure them that the odds of being harmed by such impacts remain very low. Nevertheless, you can ask them to think about questions that society is still trying to answer, such as: What agency of each government should be in charge of protecting us from asteroids? Should asteroid defense be a national or international project for Earth? What sorts of defenses against asteroids can we develop? How much public information about asteroid dangers should the government release (and when)?

    This is a topic which has inspired many movies and TV dramatizations. You might ask students if they have seen one of these, or even show one of the more popular ones, like Deep Impact or Armageddon (the first with much better science than the second.) Ask them to critique how well the movie makers did in capturing the astronomical realities of the film's situation.

    An excellent, up-to-date web site on this topic is NASA'S Asteroid and Comet Impact Hazards.

  • In 1989, parts of the Canadian province of Quebec (including the city of Montreal) were without power for up to nine hours because a storm of charged particles from the Sun had caused a surge of electricity in the power lines strong enough to knock out some of the equipment making up the power grid. This is just one example of a phenomenon astronomers are calling "space weather," a entirely new area of concern for modern civilization.

    The Sun has an eleven-year cycle of activity which students can follow. The more active the Sun is, the more dark spots which can be seen on its surface and the more flares (explosions of charged particles and energy) that can be observed in its surface layers. NASA offers an excellent presentation entitled Tracking Sunspots (PDF) for the classroom.

    It is very important to caution your students that looking at the Sun without protection can cause permanent damage to their eyes. Galileo himself realized this, so he and his assistant projected an image of the Sun through their telescope onto a wall so they could study the sunspots without harming their vision.

    If you have made contact with an amateur astronomy club near you, someone from the club may be willing to come out to the school and show students the Sun's surface, either by putting a safe filter on the telescope, or by projecting an image like Galileo did.

  • While 400 Years of the Telescope focuses mainly on the Hubble as the best-known example of a telescope in space, there are a number of other telescopes that also conduct their observations from above the Earth's atmosphere. Among these space-based observatories are the Spitzer Space Telescope (which searches for infra-red or heat waves from celestial objects), the Chandra Space Telescope (which uses x-rays), and the Fermi Space Telescope (which seeks out gamma rays). Just about a month before our show's first air date, NASA launched the Kepler Space Telescope, a more specialized mission designed to search for planets around other stars. Student groups can be assigned one space telescope to research and then report back to the class, as scientists would at their meetings, on the work of their telescope.

    One of the best decisions the people running the Hubble ever made was to quickly and freely release the beautiful images that the telescope takes as part of its research program. The Hubble images have become cultural icons and are now part of the visual vocabulary of our time. If you are studying a part of astronomy with your students, it's always fun to see if there are Hubble pictures available to go with it. The best place to check for such images is the Hubble subject index.

    It's interesting to poll your students if they have heard of the Hubble, and then ask them how far above the Earth's surface the Hubble is orbiting. Ask them to write down their answers, so they can't change them, or take a poll before revealing the answer. Most will think it is much farther away than it really is. Hubble orbits about 350 miles above the Earth's surface and takes about 97 minutes to make one full revolution around our planet. For comparison, the diameter of our planet is about 8000 miles. This would be approximately equivalent to a third of an inch above the surface of a basketball.

    The Hubble's mirror is not the largest mirror we have. In fact, with a diameter of only 94 inches, it is smaller than many of the mirrors highlighted in the film. Ask your students to brainstorm about what makes the Hubble so special as an astronomical instrument. (See the Introduction to Telescopes essay.)

  • Let's say right at the outset that this is a topic that's sometimes hard even for college students to grasp, so that any discussion with younger students is likely return many puzzled faces. On the other hand, students who have studied physics in high school may be able to relate the ideas presented in this area with some of the basic physics they have been working on.

    A good way to begin is to stand at one wall of your classroom with a piece of chalk or ball. Toss it upward so that it goes high but doesn't hit the ceiling. Ask students to explain why the ball comes down again, after it was rising so well. They should be able to respond that it is the gravity of the Earth which eventually forces the ball downward. Explain that the expansion of the universe (see our introductory essay, The Expanding Universe) is a little bit like the throwing the ball. At first, the universe goes outward from the force of the "throw" — the Big Bang — but matter in the universe has gravity, and the gravity of the universe is expected to slow (decelerate) the expansion as time passes. (In fact, if the gravity of all the matter in the universe was strong enough, then, like the ball returning to the level of the hand that threw it, the universe would eventually contract to its initial state.)

    With this background, students may now appreciate that astronomers were really surprised to measure that the universe, instead of demonstrating a decelerating expansion, was instead accelerating. It's as if the ball, while it was already in the air, suddenly went faster, crashed through the ceiling and took off into the sky since in order to accelerate an object must sense an additional force. The big mystery right now is, What force could be speeding up the entire universe?

    The notion of a new (an previously unknown) force coming to our attention is not such a radical idea. At the beginning of the 20th century, physicists began to realize that there was a very powerful force inside the nucleus of the atom. We now call it the nuclear force and it has given rise to the technologies of nuclear weapons and nuclear power. Yet before the nuclear age, few had considered such a force. Thus it is not inconceivable that the astronomical observations we are now making with large telescopes could lead scientists to understanding such a new force.

    A good book on this subject is Robert Kirshner's The Extravagant Universe (2002, Princeton University Press.)

  • Students might begin by reading our web page on Monster Telescopes, Future Telescopes. This topic connects with the topics on the development of telescopes and mirror technologies, above, and should probably follow them. The emphasis here is on building bigger "light buckets" to be able to look over longer distances, cover longer periods of time, and discover even fainter objects — all as economically as possible.

    Each of these projects will cost a considerable amount of money. You could set students searching among recent articles and web sites to get an estimate of how much each new telescope project is likely to cost and where the money is coming from. Then, students can discuss whether and why such large scientific projects are worth supporting.

    In the 1960's, Nobel Prize-winning physicist Robert Wilson was testifying at a Congressional hearing about the need for a new atom smasher (particle accelerator). He was asked whether "…anything connected with the hopes of this accelerator that in any way involves the security of this country?" Wilson replied, in part, "It has nothing to do directly with defending our country... except to make it worth defending."

  • At the very end of 400 Years of the Telescope, there is brief mention of one of the most exciting discoveries of modern astronomy. Since the beginning of 2009, scientists have discovered more than 300 planets orbiting around other stars. So far, at least 33 of the stars we are examining have more than one planet, and one star has five planets orbiting it. (We say "so far" because new planets are being discovered all the time. Since planets that take 30 years to orbit their star — as does Saturn to orbit our Sun — require at least 30 years for us to confirm their orbit, and we have only been at this about two decades, we expect many more planets to be "discoverable" as time goes on.)

    With few exceptions, we can't take a picture of a planet around another star directly. Stars are very bright and large, while planets are small and dim. Seeing a planet near its star is like trying, from an airplane, to see a small firefly near a giant spotlight at the opening of a shopping center. From far away, the firefly is far too dim to make out and it's lost in the glare of the much brighter light.

    But we can detect planets in two, more indirect ways. The first is to measure the "wiggle" of the star due to the gravity of the planet it orbits. Imagine the following far-fetched but instructive analogy: You have a very chubby dad on stage with a narrowly focused spotlight right on him. He has a small child whose hands he holds tightly as he twirls him around. The child is in the dark, outside the spotlight, so you can't see him. All you can see is the big dad, twirling around. His twirl will not be a completely steady one — he will rock slightly off-center from the pull of the swinging child. To the audience it will appear as if he is wiggling back and forth at the same rate that the child is moving around him.

    In the same way, astronomers can measure the very slight wiggle that a planet exerts on the star around which it orbits. Only since the 1990's have we been able to measure wiggles so small, but now we are quite good at it and we have found hundreds of planets by this method. Students can look at the latest information on the web to see how the search is coming. Two good web sites are NASA's PlanetQuest and The Extrasolar Planets Encyclopaedia.

    The second way we can find planets is to watch them eclipse part of their parent star — that is, to move across the face of their star as seen from Earth. While the stars still look like points of light in even the biggest telescopes, we can measure a slight decrease in the brightness of the star when a planet blocks some of its light. Astronomers call such an event a transit and this is thus called the transit method of finding planets.

    In March 2009, NASA launched the Kepler telescope into space, where it will orbit the Sun and focus its giant camera on one spot of sky. It will follow the light of 100,000 stars for about four years, checking if any of them show a repeated transit. We believe that from space the technique will allow us to catch planets as small as the Earth when they transit. Astronomers working with the telescope compare what they are trying to do with seeing a gnat fly in front of a car headlight from several miles away.

  • Students should begin by reading the essay on How Astronomers Search for Intelligent Life in Space. If you have covered the discovery of planets around other stars, you might begin by asking students whether the fact that we now know hundreds of planets out there gives them new optimism about finding extraterrestial life. Is it a leap of imagination discovering extra-solar planets to believing there is life out there that is also interested in astronomy?

    In the essay, which explains why astronomers propose to use radio waves as the means of communication with other intelligent civilizations among the stars, an analogy is given that students should be able to identify with. The essay compares finding radio signals from an alien civilization to finding a station you like on the dial when you go to a new city you have never visited before. You have to go through the dial, sorting through static and many stations before you find what you are looking for.

    Here is an analogous experiment: the SETI Institute, the scientific organization in California that is spearheading the search for extra-solar planets, has its own radio program and webcast called Are We Alone? At this writing, it is only on once a week on public radio stations in cities scattered across the U.S. (although you can listen to current and past shows right in your browser). Ask students to imagine that they had to find that show and listen to it, without knowing what cities it's playing in or what time of week or day it's on. Ask them to plan what they would have to do to find the show: it would be like looking for a needle in a haystack. And that's just the way Jill Tarter, the leader of the search, describes the astronomical problem of finding the right star, the right channel, and the right kind of signal that the "aliens" might be sending out. No wonder we haven't found anything yet.

    Ask students to discuss whether they think such a search is worthwhile. Would they be excited if we found intelligent beings around some distant star? If we do find a message from such a civilization, should we answer? This could be a decision that affects the human race. Do we humans have any system in place for making such decisions? If your students ruled the world, how would they decide?

    A good recent book on this subject is The Living Cosmos: Our Search for Life in the Universe by Christopher Impey (2007, Random House).

 

Para más información y recursos de educación es varios temas de astronomía visite las páginas web de Astronomical Society of the Pacific.

Contribuido por Andrew Fraknoi (Foothill College).

 

 

 

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