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Seeing the invisible-use of telescopes (Hirst)


Christine Hirst


Having an understanding of how filters work can allow students to investigate the necessity of viewing images in different wavelengths.


Astronomers have built an array of telescopes to observe the Sun in different 

wavelengths of light and have learned so much more than we ever could have if we only looked at the 

Sun in visible light.

Principle(s) Illustrated

  1. Increasingly sophisticated technology is used to learn about the Universe.  Visual, radio, and x- ray telescopes collect information from across the entire electromagnetic spectrum of electromagnetic waves.  

  2. Human eyes respond only to a narrow range of wavelengths of electromagnetic radiation – visible light. 


  • the sun and other stars emit energy at all wavelengths
  • light is both a particle and a wave

Materials:  (per group of 4 students) 

Styrofoam plate 

• Doctored bag of M&Ms (remove all colors except red, green, and brown) 

• _ red, _ green filter to fit over plate 

1. The Sun and other stars are made out of VERY HOT GASES.  Pour M&Ms on plate. 



• red M&Ms represent gases of the Sun with 

temperatures of 80,000 K. 

• green M&Ms represent gases of the Sun with 

temperatures of 1.5 million  K. 

• brown M&Ms represent gases of the Sun with 

temperatures of 2 million K.

2.  Astronomers use special filters to look at specific gas temperatures.

  • Place the red / green filter on top of the plate. 
  • Then, tilt the plate to slide the M&Ms to the Red (He II) filter to see features of the Sun with temperatures of 80,000 K. 
  •  Notice that the red M&Ms can be seen, while the brown and green M&Ms appear black. 

Questioning Script

Prior knowledge & experience:

  • Light is a wave
  • there are wavelengths of higher and lower energy
  • the sun and other stars emits light energy

Root question:

  • Why is there a need for different types of telescopes? 
  • What different information can each provide?

Target response:

There are telescopes which transmit images in different wavelengths, each providing different information. 

Common Misconceptions:

  • Visible light is not a wave
  • Students many not realize that stars emit light at all wavelengths
  • Students may not realize that the function of our magnetic field is to protect us from some of these wavelengths

Teacher Misconception Alert:  

Most adults would expect the visible and UV regions of the spectrum 

to have higher temperature readings than the infrared, as these wavelengths have greater energy. True. The wavelengths have greater energy than infrared wavelengths. However, the Earth’s atmosphere absorbs and scatters most of the shorter wavelengths.  Infrared has long wavelengths, and even though they have less energy than the others, there are more of them hitting the Earth and your thermometers. It is important to remember that the only purpose for this experiment is simply to have students gather evidence that the infrared part of the spectrum exists, which is proven by the infrared thermometer having a higher temperature reading than the air temperature reading. 

The sun viewed at different wavelengths

YouTube Video

YouTube Video


Outside Experiment Procedure: 

1. Move the box until  a good spectrum appears on the white paper at the bottom of the box.  To 

get a good wide spectrum, place a block underneath the prism end of the box. 

2. Place the thermometers in a shaded area of the box until all of the thermometers are reading 

the same temperature. 

3. Teacher Note:  Place the air temperature thermometer on a string in a designated location 

for all students to see. 

4. Once the thermometers have reached the same temperature, students should place a 

thermometer bulb in the blue part of the visible spectrum, one in the yellow, and the third just 

past the red part of the visible spectrum, where there is no visible light hitting the thermometer. 

Again, consider that some students might be colorblind and need assistance distinguishing 

colors of the spectrum. 

5. After 5 minutes, students should record the air and spectrum thermometer readings in the table provided in the Herschel Experiment Student Data Collection Sheet.  If a digital camera 

is available, students could take a picture of the visible spectrum produced by their group.


Light source


Christine Hirst,
Nov 16, 2011, 8:46 PM