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Samos, Grecia (//310 BC - //ca. 230 BC)
Aristarchus was a Greek astronomer and mathematician, born on the island of Samos, in Greece. He was the first person to present an explicit argument for a heliocentric model of the solar system, placing the Sun, not the Earth, at the center of the known universe (hence he is sometimes known as the "Greek Copernicus").

Astronomy is a fascinating subject to learn about on television and the Internet. But it’s even more enjoyable to experience astronomy firsthand! Here we present some ways for you and your family to view celestial objects and meet amateur astronomers – from beginners to experts – who can help you learn more about telescopes, binoculars, the night sky, observing techniques and what’s happening in the field of astronomy right now. Use the resources in this section to find an astronomy club, planetarium or science center near you where you can ask questions and get started on your own personal journey of discovery. You can also find an introduction to telescopes and sky gazing here.

  • After watching the show, your family may want to find ways to pursue astronomy as an interest or a hobby. At the very least, you may want to take advantage of the International Year of Astronomy in 2009 to give everyone in your family a look through a telescope. Here are some ways everyone can get more involved:

    1. Find an amateur astronomy club near you and go to a "star party" (an evening observing session with telescopes) or one of their meetings with interesting speakers.

    2. Go to a local planetarium (sky theater), especially if it is showing "Two Small Pieces of Glass" (the planetarium program associated with 400 Years of the Telescope). See Find a Planetarium or Science Center Near You, below.

    3. Check out the IYA Calendar to see if there are special programs or astronomy gatherings in your area.

    4. Try one of the following fun astronomy activities with your family:

      Astronomy in the Marketplace, where family members come up with as many astronomically named products as they can.

      Making and Using a Family Star Finder, where the family uses simple materials to build a star-finder wheel that lets you dial up the bright stars and constellations for any month of the year.

      Toilet Paper Solar System, where everyone gets to unroll a roll of toilet paper to make a scale model of the planets that orbit the Sun.

    These activities are provided by the Family ASTRO Project at the Astronomical Society of the Pacific and are used with their kind permission. Visit for more information.

  • The fascination of astronomy attracts people of all ages and from many different walks of life. All around the United States (and the world), astronomy enthusiasts have organized "amateur astronomy clubs" that hold regular meetings (with speakers), offer star parties (times to go outside to a dark location and bring telescopes), and hold outreach activities for the public.

    Those astronomy clubs that are especially interested in working with teachers and the public are part of the Night Sky Network, supported by NASA through the Jet Propulsion Laboratory and organized by the Astronomical Society of the Pacific. The Night Sky Network is partnering with the producers of 400 Years of the Telescope and selected PBS stations around the country to offer public events in connection with the show. Many events will be part of the celebration of the International Year of Astronomy in 2009.

    To find out more about these events, visit our IYA Calendar page.

    To find an astronomy club near you, see:

    The Night Sky Network Club Finder

    Sky & Telescope Magazine Club Finder

    Astronomy Magazine Club Finder:

    Astronomical League Club Directory:

  • As you can see elsewhere on this web site, 400 Years of the Telescope is accompanied by a planetarium program called Two Small Pieces of Glass.

    A planetarium (or star theater) is a domed auditorium in which we can project a simulation of the night sky. Planetaria are located in many different kinds of settings -- schools, colleges, museums and science centers, and in their own buildings. Among the best known ones in the U.S. are the Rose Center/Hayden Planetarium in New York City, the Adler Planetarium in Chicago, and the Griffith in Los Angeles.

    See our IYA Calendar to see if a showing of Two Small Pieces of Glass or some other International Year of Astronomy event is scheduled at a planetarium near you, or check out the following websites:

    Planetarium Finder from the International Planetarium Society

    Planetarium Compendium from Loch Ness Productions

    Astronomy Organizations from Sky & Telescope Magazine:

  • If watching 400 Years of the Telescope kindles your interest in astronomy, this page is designed to give you some friendly hints for getting to know the night sky.

    While the lights of civilization and clouds and fog often make it hard to see the stars, get away from cities on a clear night, and you will be amazed at the sparkling tapestry of stars over your head. Earlier cultures looked in awe at the thousands of stars visible to the naked eye, and began to search for simple patterns among the brightest ones. People would call the patterns formed by the brighter stars constellations. (1)

    Getting to know the constellation patterns (and the brighter stars that make them up) is a challenge similar to getting to know the streets of a new town. You need a good map, lots of time, and patience with the process. Taking someone with you who already knows the town can be a big help too -- which is why we always recommend finding an astronomy club near you.

    The maps of a city change slowly, and are usually good all year long. But those who use maps of the sky have to consider that the sky is different at different times of the night and different months of the year. This is because the Earth is a moving platform from which to watch the sky. Hour by hour, the stars we can see change because the Earth is turning -- spinning on its axis. And month by month, the stars change because we are orbiting around the Sun and thus seeing different stars at night.

    As a result, a good star map will also turn -- that is, it will let you "dial up" the right time of night and the right month of the year to show you the right sky patterns. Such turning-dial maps are called planispheres. You can buy a planisphere through many science stores and even in larger book stores. Or you can make your own at home with our family star finder activity.

    If you go out with a planisphere under the stars, you'll want to dress warm and bring a flashlight to read you star map. A white light will be a problem for your night vision (your eyes open wide in the dark, but constrict when they are hit with light). It helps to have a red flashlight, which is much less harmful to your night vision. You can make one by putting a piece of red cellophane, a red sock or t-shirt, or even part of a brown paper bag over your flashlight and securing it with a rubber band.

    If getting to know the night sky whets your family's appetite for getting a telescope, the best advice we can give you is to go slow. Don't be fooled by departments store ads or fast-talking salesmen. Buying a telescope is like buying a car or computer; the more you know before you buy, the happier you are likely be with your purchase.

    Start by borrowing a pair of good binoculars (if you can) and scanning the sky with those. Then attend a "star party" (sky observing session) held by your local amateur astronomy club, observatory, or college, and get to know (and try out) the different types of telescopes. Many telescope owners (like dog owners) love to talk about their telescope and to give advice. The two main astronomy hobby magazines, Astronomy and Sky & Telescope, are both full of articles, reviews, and ads to help you find a telescope that's right for you. Most large libraries have back issues that you can browse.

    However you begin your odyssey into greater enjoyment of the stars, we wish you clear skies, dark nights, and hours of enjoyment.

    (1) Today, astronomers have gone a step further in organizing the sky for easy reference. They divide the sky around the Earth into 88 unevenly-shaped boxes or sectors -- much as the continental United States is divided into 48 unevenly-shaped boxes called states. Each of the 88 sky boxes is named after an ancient constellation that happens to be in it -- usually from Greek and Roman mythology. Thus the box containing the pattern of Orion the hunter is also given the name Orion. Everything in the sky falls into one of the 88 constellation boxes.

  • Four Hundred Years of the Telescope tells the dramatic story of how a simple instrument, put to use by brilliant astronomers, transformed our view of the universe and of ourselves. But, what exactly is a telescope, and how does it work?

    Light Buckets

    Telescopes are devices to collect far more light than our eyes can bring together, and thus make things visible that are otherwise too faint for us to see. Telescopes can also magnify things (make them look bigger), something that is important if you are looking for the color of a bird in a tree or spying on your neighbors, but this is often less important for astronomers than sheer light-gathering power.

    Think of telescopes as giant buckets for collecting light. If there has been a drought, and you run outside to catch the water from a sudden rainstorm, you will be disappointed if all you have with you is a small paper cup. Can't catch much rain in that! But if you could grab a big bucket, or even bring a picnic cooler outside, then you can collect more rain and perhaps water a few of your indoor plants.

    Telescopes work the same way. The bigger the element in the telescope that collects and focuses the light, the more light you can gather from an object in the sky. Light gathering power depends on the area of the lens or mirror collecting light. Since the lenses in our eyes are so small (designed for looking at a sunlit scene), even Galileo's small telescope was able to gather about 100 times as much light as the human eye. This is how Galileo was able to see the moons of Jupiter, when no one had ever been able to see them before. The extra light collected made things in the night sky that were too faint for the unaided eye to see suddenly visible.

    Scientists sometimes joke that the history of astronomy can be summed up as a search for bigger light buckets. Every time we have built a larger collector of light (or other waves), we have discovered things that were too faint to be detected before -- and opened up new worlds for exploration. The show gives a nice overview of how astronomers and engineers have worked together to build bigger and more efficient telescopes.

    Types of Telescopes

    The first telescopes used a lens to collect, bend, and focus light (just like our eyes do). But lenses have a number of disadvantages. As you know from the lenses in eyeglasses, the lens requires both sides to be clear. That's why the lenses in your uncle's glasses are held only around the edges. The larger the lens, the more it tends to sag because of its weight. And lenses tend to bend different colors of light differently, which made the various colors spread out in an image. We can compensate for these disadvantages up to a point, but large light buckets made with mirrors turn out to be significantly easier to construct.

    It was the great physicist Isaac Newton who first showed how to make a practical telescope using mirrors. The big advantage of a mirror as your light bucket is that the light reflects off the mirror surface -- it doesn't go through the mirror like it does for a lens. Therefore only one side of the mirror must be kept clear and the bottom side can be used to hold and support it. Mirrors, when made the right shape, also don't separate the colors of light like lenses do. For these and other reasons, mirrors can be made much larger than lenses and all the modern telescopes astronomers use are "reflectors."

    As discussed in the show, astronomers have found ingenious ways to make bigger and bigger mirrors in recent decades. Some giant mirrors are made from several segments which are kept aligned by computer-controlled devices. Other mirrors are made while the hot mirror material is spun at high speed and can be made much more light-weight through this process. Sometimes several large mirrors are used in the same telescope and the light they collect is brought together to make the equivalent of a much bigger mirror. As a result, we have light buckets today that Galileo and Newton did not even dare to dream about.

    Resolving Power

    Another important characteristic of a telescope is its resolving power -- its ability to make out fine detail. In theory, the bigger the telescope, the better its resolving power -- the finer the detail it can make out -- whether we are looking at the weather on Jupiter, or the collision of two far-away galaxies of stars. Thus, another reason that astronomers build larger telescopes is to try to see the inner workings of distant objects.

    Alas, many large telescopes cannot see fine detail anywhere near as well as theory predicts. That's because telescopes on Earth have to look through miles of air -- and our atmosphere dances, jiggles, and is full of water vapor, ash, and human pollution. The dancing and blurring of images by our atmosphere is the reason stars appear to twinkle when we look at them from the ground. The higher up we put our telescope, the less air it has to look through and the clearer our view. This is why all observatories with large telescopes are built on high mountaintops, where the air is clear and clean.

    As you can imagine, the best solution to the blurring effects of air is to rise above the problem -- literally. Telescopes above our atmosphere, such as the Hubble Space Telescope, can enjoy the resolving power that laws of physics promise, but don't deliver on Earth.


    A telescope is a passive collector of light (or other waves), just as your car antenna is a passive collector of waves from local radio stations. Before you can listen to the news and traffic, you need to attach that antenna to a detector, a device that actually receives the waves and can record or translate them. In the case of your radio, the detector is your radio set, which turns the radio waves sent by your favorite radio station into sound you can hear.

    Telescopes also need detectors attached for us to be able to see the images they form. For centuries after Galileo, the only available detector was the human eye. Astronomers made sketches of what they saw -- we still treasure those early sketches for the pioneering information they contain. But in the second half of the 19th century, the invention of photography changed astronomy profoundly. A photograph allows us to make a permanent record of what is in the sky -- a record that is not fooled by the prejudices of the human brain, as early observers sometimes were.

    Even more important, photographs allow us to add together the light that comes in over many minutes or even hours. This is called a long exposure, and it has the same effect as getting a bigger light bucket -- you can collect more light and see things in the sky that are fainter. It was photography that made the studies of galaxies discussed in our show possible and led to the discovery of the expanding universe.

    Today, digital photography allows astronomers using electronic cameras to record even fainter objects than ever. Electronic detectors (whose technical name is CCD's) have revolutionized our search for faint objects -- such as asteroid, dwarf planets, or exploding stars in other galaxies. Together huge telescopes and super-efficient detectors are giving us unprecedented views of the universe. This is the revolution that 400 Years of the Telescope celebrates.

    Contributed by Andrew Fraknoi (Foothill College)

  • This is a brief guide to books and materials you can use to get more involved with the night sky and astronomy. It is not comprehensive, but offers some well-regarded resources for beginners.

    Download this resource guide here: PDF




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