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23.2: Lesson 23.1: Telescopes

Difficulty Level: At Grade Created by: CK-12

Key Concepts

  • Electromagnetic spectrum and electromagnetic waves
  • The speed of light
  • Optical, radio, and space telescopes
  • Observations made with telescopes
  • Studying starlight with spectrometers

Lesson Objectives

  • Explain how astronomers use light to study the universe beyond Earth.
  • Describe some different types of telescopes.
  • Discuss what we have learned by using telescopes.

Lesson Vocabulary

  • constellation: group of stars that appear from Earth to form a recognizable pattern
  • electromagnetic radiation: energy transmitted through space as waves
  • electromagnetic spectrum: total range of wavelengths of electromagnetic radiation
  • frequency: number of waves that pass a given point each second
  • gamma ray: type of electromagnetic radiation that has the shortest wavelengths
  • infrared light: type of electromagnetic radiation that has wavelengths longer than visible light but shorter than radio waves and that humans can feel as heat
  • light-year: distance light can travel in one year; equal to 9.5 trillion kilometers
  • microwave: type of electromagnetic radiation with wavelengths between radio waves and infrared light; generally considered to be high-frequency radio waves
  • planet: object in space that orbits a star and has cleared its orbit of smaller objects
  • radio telescope: type of telescope that collects radio waves instead of visible light
  • radio wave: type of electromagnetic radiation that has the longest wavelengths
  • reflecting telescope: type of optical telescope that uses mirrors to collect and focus visible light
  • refracting telescope: type of optical telescope that uses lenses to collect and focus visible light
  • space telescope: telescope that is placed into orbit around Earth above Earth’s atmosphere
  • spectrometer: device that breaks light into different wavelengths, or colors
  • ultraviolet light: type of electromagnetic radiation that has wavelengths shorter than visible light but longer than X-rays and that harms living things
  • wavelength: horizontal distance between corresponding points on two adjacent waves, such as the distance between two crests or two troughs
  • visible light: type of electromagnetic radiation that has wavelengths between ultraviolet and infrared light and that can be detected by the human eye
  • X ray: type of electromagnetic radiation with wavelengths between ultraviolet light and gamma rays

Teaching Strategies

Introducing the Lesson

Introduce students to space by helping them recall where Earth’s atmosphere ends and space begins.

Question: What is the outermost layer of the atmosphere?
Answer: The outermost layer of the atmosphere is the exosphere.
Question: How far out does it extend?
Answer: Because the exosphere gradually fades into outer space, there is no clear upper boundary to this layer of the atmosphere.

Explain that some scientists put the upper boundary of Earth’s atmosphere at about 100,000 km (62,000 miles) above Earth’s surface. Other scientists extend it to about 190,000 km (120,000 miles) above Earth’s surface. Point out that space is considered to begin where the exosphere leaves off. Tell students they will start learning about space in this chapter.


Students can use an interactive animated reflecting telescope at the following URL to gain a deeper understanding of how a reflecting telescope works.


Building Science Skills

The light-year is a difficult concept for some students to grasp. Use the fun activity at the URL below to help students understand it. They will generate their own unit of measurement based on the distance they travel in a set time interval and then draw parallels between their unit and the light-year.



Students can learn about the wavelengths, frequencies, and energy levels of different types of electromagnetic waves with the “Spin-A-Spectrum” manipulative at the following URL. The teacher’s guide for the activity presents a series of riddles that require students to know facts about the electromagnetic spectrum and which objects are best observed in each region of the spectrum.


Differentiated Instruction

Have students make a compare/contrast table for refracting and reflecting telescopes. The table might compare and contrast the two types of telescopes in terms of how they gather and focus light, which type was invented first, and which type is potentially stronger.


Students can make a star finder by following the instructions at the following URL. Then they can use it learn their way around the night sky by finding constellations. The Web site includes a star finder game and background information on stars and constellations.


Science Inquiry

Students are likely to think that the stars in constellations are actually grouped closely together in space. In fact, most are located at very different distances from Earth. The activity at the URL below will help students realize that the sky is not just a dome as it appears from Earth but a three-dimensional space and that objects that look like they are grouped together may actually be very far apart.


History Connection

Help students appreciate the significance of Galileo’s discoveries with the telescope, in particular, the evidence his discoveries provided for the Copernican view of the solar system. Have students watch the video clip at the following URL. In the clip, actors play Galileo and Copernicus in a game show, in which they explain the sun-centered theory of the solar system and some of the evidence for it.


Reinforce and Review

Lesson Worksheets

Copy and distribute the lesson worksheets in the CK-12 Earth Science for Middle School Workbook. Ask students to complete the worksheets alone or in pairs to reinforce lesson content.

Lesson Review Questions

Have students answer the Review Questions listed at the end of the lesson in the FlexBook® student edition.

Lesson Quiz

Check students’ mastery of the lesson with Lesson 23.1 Quiz in CK-12 Earth Science for Middle School Quizzes and Tests.

Points to Consider

Radio waves are used for communicating with spacecraft. A round-trip communication from Earth to Mars takes anywhere from 6 to 42 minutes. What challenges might this present for sending unmanned spacecraft and probes to Mars?

The Hubble space telescope is a very important source of data for astronomers. The fascinating and beautiful images from the Hubble also help to maintain public support for science. However, the Hubble is growing old. Missions to service and maintain the telescope are extremely expensive and put the lives of astronauts at risk. Do you think there should be another servicing mission to the Hubble?

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