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Online Discovery – Astronomy Week One Basic Astronomical Vocabulary Lesson Plan

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Date: 1992

Grade(s): 4, 5, 6


  • Science/Astronomy

Outcomes: You will to the best of your ability:

  • Define basic astronomical vocabulary.
  • Describe two major types of telescopes.
  • Build and use a telescope.
  • Introduction:

    On a warm summer night as you have gazed at the sky, have you wondered about the twinkling stars and the bright moon? Like early man all of us are overcome by the wonders in the night sky. This interest has led many people to study the stars, planets, and other objects that make up the sky. This study is known as astronomy. A person who has made it her job to study the objects in the sky is known as an astronomer. But there are many other people who study astronomy as a hobby.

    To help you learn astronomy we will be doing some fun activities, including building a telescope and charting the phases of the moon.


    When you were beginning to read you learned words and how to pronounce and spell them. Soon you could put words together and read a sentence. Then you could read a paragraph; then a story; then a book. Your experience in studying astronomy is the same. First you must learn the vocabulary of astronomy. Then you need to study the workings of the solar system. Soon you will find that you have a basic understanding of astronomy.

    Let’s begin with step one by learning the basic vocabulary of astronomy. Look up in a dictionary, encyclopedia or other book the definitions of the words found on pages 1 – 15 of your Student Astronomy Resource Book. Write their pronunciations and definitions in your Student Astronomy Resource Book. Draw a picture of the word you are defining.


    Word: Sun
    Pronunciation: (sún)
    The luminous celestial body around which the earth and other planets revolve, from which they receive heat and light, and which has a mean distance from earth of 93,000,00 miles (150,000,000 kilometers), a linear diameter of 864,000 miles (1,390,000 kilometers), a mass 332,000 times greater than earth, and a mean density about one-fourth that of earth. Your Definition: The bright star around which the earth and other planets revolve.

    Your Drawing:


    Because the stars, planets, comets and other objects in space are so far from the earth, we need special instruments to study them. All stars, including the sun, send energy out into space. Much of this energy is in the form of visible light. Optical telescopes have been developed to collect the light from the stars. Optical telescopes use large lenses or mirrors to gather more light. This way faint objects can become visible to our eyes.

    Telescopes can also magnify images, but this is not the main function of a telescope. The atmosphere or the air around the earth makes the stars appear to twinkle and move. This prevents a clear view of the star no matter how large it appears. Since most stars are so far away, they still appear as points of light even with high magnification. The main purpose of an optical telescope is to collect light. A telescope can gather even more light if it is used with a camera. If the film in the camera is exposed to light for a long time the light adds up and makes a better picture.

    Class Activity:

    An eye, a camera, and an optical telescope are all alike. They all collect light. Notice that they all have openings that allow light to pass, they gather light, and they all receive images. Your eye adjusts to the amount of light it gathers by adjusting the size of the iris and pupil. A photographer can take a picture in dim light without a flash by either adjusting the iris of the camera or by slowing the speed of the shutter. Study the diagrams of the eye, camera, and optical telescope.

    Then make a chart showing the similar parts . (See diagrams zero, one, and two in Online Discovery – Astronomy Teacher Aid Book.)

    The first optical telescopes were made in the early 1600s. Galileo made the first telescope to study the universe. He used a refracting telescope, (See diagram one in Online Discovery-Astronomy Teacher Aid book.) a telescope that uses lenses to collect light. A simple refracting telescope basically consists of a tube with a lens at both ends. Light enters through the objective lens and is bent toward a single point called the focal point. The bent or refracted light causes the image to form upside down. The second lens is called the eyepiece which magnifies the upside-down image for viewing. To focus this kind of telescope you can change the distance between the two lenses. The most powerful telescope Galileo made magnified objects 33 times which is no more than most binoculars. With this instrument he discovered the phases of Venus, four moons around Jupiter, and craters on the moon.

    Reflecting telescopes use mirrors instead of lenses to collect light. (See diagram two in Online Discovery-Astronomy Teacher Aid book.) One end of the tube is open which allows light to pass to the large curved mirror called the primary mirror or objective at the other end of the tube. A smaller flat mirror or secondary mirror is placed at an angle near the tube’s open end. An eyepiece is a lens on the tube’s side. The large mirror collects and reflects the light to the smaller mirror which reflects the light to the eyepiece. The largest telescopes today are reflecting telescopes. They have such big mirrors that they can collect light from objects over a million times fainter than the unaided eye can see.


    On pages 16-19 of your Student Resource Book add the following words to your astronomical vocabulary dictionary: optical telescope, refracting telescope, objective lens, and eyepiece. Remember to write their pronunciations, definitions, and your definitions.

    Investigation: How Lenses Refract Light

    Adapted from Scott Foresman, Earth Science, 1990


  • two convex lenses with different diameters
  • ruler
  • index card
  • clay
  • Procedure:

  • Secure the lenses and index card in clay on the ruler so that the objects stand upright. Try to shape the clay around the rim of the lenses so that as much of the lenses are exposed as possible. Place the card between the two lenses.
  • Aim one end of the ruler at a window or other source of light. (Warning: do not stare directly into the sun!) A candle may also be used. Do not tilt the ruler.
  • Carefully slide the lens closest to the light source back and forth until a sharp image appears on the card. Measure and record the distance between the card and the lens. This distance is the focal length of that lens.
  • Carefully turn the ruler around so that the other lens is facing the light source. Be sure not to move the lenses or the card.
  • Now slide this lens until a sharp image appears. Measure again to find the focal length of this second lens. Record this number.
  • Point the end of the ruler that has the lens with the longer focal length toward an object in the room. Remove the card from the ruler but don’t move the lenses.
  • This is a simple refracting telescope. Look at the object through the lenses.
  • Analysis:

  • Which lens served as the objective lens? Which was the eyepiece?
  • Determine the magnifying power of your telescope using this formula:

      Magnification = focal length of the objective divided by the focal length of the eyepiece.

  • How is the image of an object seen through the telescope different from the object itself?
  • What would happen if you used the lens with the longer focal length as the eyepiece?

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