Introduction

Chapter 5. Observing Infrared Radiation

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Infrared Portrait

Author: Grace L. Deming, University Of Maryland

Editor: Beth Hufnagel, Anne Arundel Community College

Infrared Portrait
An Infrared Portrait

The goals of this module: After completing this exercise, you should be able to:

  1. Recognize that humans can see only a small range of wavelengths of light, the visible spectrum.
  2. Describe light as having a range of wavelengths (or frequencies or energies) called a spectrum.
  3. Compare the information contained in visible and invisible light emitted by objects of differing temperature.

In this module you will explore:

  1. Wave properties of visible and invisible light.
  2. How an object's temperature affects emitted light.

Why you are doing it: By understanding that an object's temperature can be revealed by studying the light that it emits, you can learn how astronomers are able to determine the temperature of a distant celestial object. In addition to light that we see using our eyes, there are other forms of light that are invisible.

Electromagnetic Spectrum Figure
The Electromagnetic Spectrum

Light, also described as electromagnetic radiation, includes invisible as well as visible forms. Study the figure to the right that shows the entire electromagnetic spectrum.

  • Gamma rays
  • X-rays
  • ultraviolet radiation
  • infrared radiation
  • microwaves
  • radio waves

are forms of invisible electromagnetic radiation.

Locate these regions on the figure. Notice that your eyes are sensitive to a very small portion of the electromagnetic spectrum. Electromagnetic radiation can be described by a specific wavelength, frequency, and energy. Wavelengths are shown on the figure. Find the two forms of electromagnetic radiation that are associated with the greatest energy.

Notice that these two forms have the shortest wavelengths. Locate the longest wavelength region shown. How does the energy of this region of the electromagnetic spectrum compare to the shorter wavelength regions?

The NASA video presentation "Infrared: More Than Your Eyes Can See" features the infrared region of the spectrum. How does the infrared region compare to visible light in terms of wavelength (longer or shorter than visible light) and energy (greater or less than visible light)?

Watch the video presentation.

After viewing, answer the following questions:

Question Sequence

Question 1.

Your body is warm, so this means that you are emitting infrared radiation right now.

A.
B.

Correct. Humans are emitting infrared radiation, which is a form of energy. The infrared camera shown in the video detects the infrared radiation (heat) that you emit and uses it to create an image.
Incorrect. Humans are emitting infrared radiation, which is a form of energy. The infrared camera shown in the video detects the infrared radiation (heat) that you emit and uses it to create an image.
Python Figure
People holding a python

The animals that were shown in the video presentation appeared very different. When using an infrared camera, the image is displayed using colors to indicate the corresponding temperature. The colors can be correlated to temperature using a scale, making it very easy to understand which areas are warmer and which are cooler.

Visit this website and compare the images and the temperatures of the Macaw (bird), cat (mammal), and turtles (reptiles). Study the temperature scale given next to each image.

How does the human's temperature compare to the Macaw's temperature? Are they warmer or cooler than their surroundings? Could you see the warm footprints the cat left?

Turtle Figure
Turtle Temperature Figure

Question 3.

Why do the turtles look different in the two infrared images at the bottom? The turtle on the right

A.
B.
C.

3
Try again.
Correct. These images demonstrate how infrared images can be used to detect temperature differences in animals and celestial objects. The turtles on the left just came out of the water so they're cooler.
Incorrect. These images demonstrate how infrared images can be used to detect temperature differences in animals and celestial objects. The turtles on the left just came out of the water so they're cooler.

Astronomers are interested in using infrared cameras to learn more about celestial objects. For these purposes, it is beneficial to divide the infrared region into three sub-regions: the near-infrared, the mid-infrared, and the far-infrared. The prefixes refer to each region's location relative to visible light. For example, the near-infrared is closest in wavelength to red visible light, while the far-infrared has much longer wavelength than visible light.

Visit this website to learn more about what astronomers "see" when they use infrared cameras to study the cosmos.

Consider the Table highlighting which kinds of objects can be studied by collecting infrared data.

Question Sequence

Question 4.

Which celestial objects are prime candidates to be studied in near-infrared light?

A.
B.
C.
D.
E.

3
Try again.
Correct. The near-infrared region of the spectrum can be used to study cooler red stars, including red giants. Dust is transparent to near-infrared, so astronomers can see deeper into dusty regions in space than if using visible telescopes. The mid-infrared is useful when studying planets, comets and asteroids. Any dust that is warmed by starlight also shows up, as well as any protoplanetary disks (dusty regions surrounding forming stars where planets may be forming). The far-infrared region can be used to pick up emission from cold dust and very cold molecular clouds. The central regions of galaxies are bright in this region of the spectrum.
Incorrect. The near-infrared region of the spectrum can be used to study cooler red stars, including red giants. Dust is transparent to near-infrared, so astronomers can see deeper into dusty regions in space than if using visible telescopes. The mid-infrared is useful when studying planets, comets and asteroids. Any dust that is warmed by starlight also shows up, as well as any protoplanetary disks (dusty regions surrounding forming stars where planets may be forming). The far-infrared region can be used to pick up emission from cold dust and very cold molecular clouds. The central regions of galaxies are bright in this region of the spectrum.
Infrared Galaxy Figure

Indepth Activity: Observing Infrared Radiation

Question 6.

The wavelength of infrared radiation:

A.
B.
C.
D.
E.

Correct.
Incorrect.

Question 7.

Cold-blooded animals aren't warm so they:

A.
B.
C.
D.
E.

Correct.
Incorrect.

Question 8.

____________ are more energetic than ____________ radiation.

A.
B.
C.
D.
E.

Correct.
Incorrect.

Question 9.

Which electromagnetic radiation has the longest wavelength?

A.
B.
C.
D.
E.
F.

Correct.
Incorrect.

Question 10.

Which electromagnetic radiation has the highest energy?

A.
B.
C.
D.
E.
F.

Correct.
Incorrect.

Question 11.

Which electromagnetic radiation do humans use the most?

A.
B.
C.
D.
E.
F.
G.

Correct.
Incorrect.

Question 12.

What is one advantage infrared astronomy has over visible light astronomy?

A.
B.
C.
D.
E.

Correct.
Incorrect.

Question 13.

If you could only see in infrared light, which of the following would be hardest to see?

A.
B.
C.
D.
E.

Correct.
Incorrect.

Question 14.

Infrared cameras can be used to determine differences in

A.
B.
C.
D.

Correct.
Incorrect.

Question 15.

In the emission spectrum for sodium, two bright yellow lines are visible. As the temperature of the sodium increases, these lines

A.
B.
C.

Correct. You observed the emission lines increasing in intensity in the first 'Background' animation.
Incorrect. You observed the emission lines increasing in intensity in the first 'Background' animation.
Trifid Nebula Figure
Visual and infrared images of the Trifid Nebula

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