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Ch 4: Light in Astronomy

About This Chapter

Watch online science video lessons to learn about electromagnetic waves, star spectra, the speed of light and more. These lessons are just a portion of our college-level astronomy course.

Light in Astronomy - Chapter Summary and Learning Objectives

Use the lessons in this chapter to discover characteristics of visible light and learn how this region of the electromagnetic spectrum helps us study stars and other celestial objects here on Earth. Instructors explain the basic wave properties and behaviors that allow scientists to disperse the light from stars into spectra used to identify their intrinsic properties, like temperature and chemical composition. This chapter is designed to teach you about:

  • Regions of the electromagnetic spectrum
  • Wave refraction, reflection, dispersion and diffraction
  • Star properties and the appearance of spectra
  • Star brightness and the speed of light

Video Objectives
What is Light? Discuss the basic wave properties and quanta of visible light.
The Nature of Light: Origin, Spectrum & Color Frequency Examine the range of visible light found on the electromagnetic spectrum. Study the wavelength of each color frequency.
Electromagnetic Waves: Definition, Sources & Properties Explore frequencies of waves at either end of the visible light range. Identify sources of electromagnetic radiation.
The 7 Major Regions of the Electromagnetic Spectrum Get examples of the electromagnetic spectrum's radio waves, microwaves, infrared radiation, visible light, ultraviolet light, x-rays and gamma rays.
Reflection: Angle of Incidence and Curved Surfaces Describe wave behavior when it strikes a surface. Use the law of reflection to describe the angles of incident and reflected rays.
Resonance: Definition & Transmission of Waves Study the relationship between objects' resonant frequency and the transmission of light or sound waves.
Transparent and Opaque Materials in Electromagnetic Waves Learn how the absorption, reflection or transmission of light waves determines whether an object is transparent or opaque.
Color: White Light, Reflection & Absorption Discover why our perception of color depends on the wavelength of visible light being reflected from an object.
Refraction & Dispersion: Definition, Snell's Law & Index of Refraction Use Snell's law to describe the ratio between the angle of incidence and angle of refraction for a ray traveling through a medium. Explain the dispersion of white light.
Diffraction: Relation to Sound & Light and Effects of Wavelength Describe the behavior of light and sound waves as they bend around barriers or pass through their openings.
Wave-Particle Duality: Concept, Explanation & Examples Explain how the photoelectric effect demonstrates light's behavior as a particle stream.
The Source and Appearance of Spectra Differentiate between the sources of continuum, absorption and emission spectra. Describe their appearances.
Spectra Images & the Emission or Absorption of Light Explore the relationship between atoms' absorption or emission of light and the appearance of spectra.
Intrinsic & Apparent Properties of Stars Distinguish luminosity, chemical composition and other intrinsic star properties from apparent properties, like observed brightness.
Comparing Star Brightness & Color Using the Magnitude System Compare stars' colors and brightness using the magnitude system.
The Speed of Light Explain what a light year is. Use it to describe the relationship between distance and time.

19 Lessons in Chapter 4: Light in Astronomy
Wave Parameters: Wavelength, Amplitude, Period, Frequency & Speed

1. Wave Parameters: Wavelength, Amplitude, Period, Frequency & Speed

How do we measure and describe waves? How do waves differ based upon their shapes? This lesson will guide you through the five wave parameters - period, frequency, amplitude, wavelength, and speed - that we use to characterize waves.

What is Light?

2. What is Light?

This lesson will define and describe what light is from both technical and more common-use perspectives, discuss what the different kinds of light are, and explain why it's called radiation.

The Speed of Light: Distance & Light-Years

3. The Speed of Light: Distance & Light-Years

This lesson will tell you what the speed of light is, what a light year is, what lookback time is, and why it is that we see many objects in space as they were a long time ago.

The Nature of Light: Origin, Spectrum & Color Frequency

4. The Nature of Light: Origin, Spectrum & Color Frequency

This lesson introduces the basics of visible light and color. Learn how the visible light spectrum is divided into the six color ranges. We'll also discuss why different people name colors in different ways.

Electromagnetic Waves: Definition, Sources & Properties

5. Electromagnetic Waves: Definition, Sources & Properties

In this lesson, learn the basics of electromagnetic waves and how they make up the electromagnetic spectrum. We will explore the major trends and categories within the spectrum, as well as the various sources of electromagnetic waves.

The 7 Major Regions of the Electromagnetic Spectrum

6. The 7 Major Regions of the Electromagnetic Spectrum

This lesson will walk you through each of the major regions of the electromagnetic spectrum. Explore the unique characteristics of X-rays, microwaves, radio waves, UV rays, infrared, gamma rays, and of course, visible light.

Reflection: Angle of Incidence and Curved Surfaces

7. Reflection: Angle of Incidence and Curved Surfaces

How do waves reflect off of surfaces? How do we account for the images that we see reflected in various objects? Discover the answers to these questions as we investigate the rays and angles defining the law of reflection.

Refraction & Dispersion: Definition, Snell's Law & Index of Refraction

8. Refraction & Dispersion: Definition, Snell's Law & Index of Refraction

Refraction explains why light bends in water. But, did you know that mathematical laws determine exactly how light waves are bent? In this lesson, we'll explore the mechanics of wave refraction, including Snell's Law and the index of refraction.

Diffraction: Relation to Sound & Light and Effects of Wavelength

9. Diffraction: Relation to Sound & Light and Effects of Wavelength

This lesson explores diffraction as one of the many behaviors of waves. Learn how diffraction occurs in sound and light waves and how it is affected by the wavelength of a wave. Find out how animals use diffraction to communicate and how scientists use it to study molecules.

Resonance: Definition & Transmission of Waves

10. Resonance: Definition & Transmission of Waves

This lesson describes how sound and light waves are affected by the principle of resonance. Learn how resonance occurs through the vibrations and resonant frequencies of objects. You'll investigate everyday examples of resonance and learn how to break a wine glass with your voice!

Color: White Light, Reflection & Absorption

11. Color: White Light, Reflection & Absorption

What gives color to objects? How do light waves interact with materials to produce red and green or white and black? In this lesson, learn how white light is composed of all colors and how absorption and reflection influence our color perception.

Transparent and Opaque Materials in Electromagnetic Waves

12. Transparent and Opaque Materials in Electromagnetic Waves

What makes an object transparent or opaque? How does light pass through some objects and not others? And what about the other types of electromagnetic waves? We'll investigate all these questions in this lesson about the transparency and opacity of materials.

Wave-Particle Duality: Concept, Explanation & Examples

13. Wave-Particle Duality: Concept, Explanation & Examples

Is light a particle with mass and substance? Or, is it just a wave traveling through space? Most scientists say light is both a particle and a wave! Find out how they came to this strange conclusion as we learn about the theory of wave-particle duality.

How Light & Matter Interact

14. How Light & Matter Interact

This lesson will go over the fundamental basic of how light and matter interact with one another. You'll learn about photons, excited atoms, binding energy, and energy levels.

Blackbody & Blackbody Radiation Theory

15. Blackbody & Blackbody Radiation Theory

This lesson will go over the perfect absorber and emitter of radiation, something called a blackbody, as well as the concept of blackbody radiation and electromagnetic radiation.

What Are Wien's Law & the Stefan-Boltzmann Law?

16. What Are Wien's Law & the Stefan-Boltzmann Law?

This lesson will explain why an object glows and why it changes color with temperature as we take a look at blackbodies, electromagnetic radiation, Wien's Law, and the Stefan-Boltzmann Law.

Calculations with Wien's Law & the Stefan-Boltzmann Law

17. Calculations with Wien's Law & the Stefan-Boltzmann Law

This lesson will go over the equations, as well as some calculations, for Wien's law and the Stefan-Boltzmann law. You will learn what factors these laws depend upon and what they reveal.

Quantum Physics: Definition, Theories & Topics

18. Quantum Physics: Definition, Theories & Topics

In this lesson, you will learn what quantum physics, otherwise known as quantum mechanics, is, some of its theories and topics, and the weird consequences that go along with it. A short quiz will follow.

What is a Photon? - Definition, Energy & Wavelength

19. What is a Photon? - Definition, Energy & Wavelength

In this lesson, we will learn the definition of a photon. We will also explain Planck's constant and its relationship to the photon energy and wavelength. The calculation of photo energy is also demonstrated.

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