Ch 21: The Earth, Sky, and Moon

About This Chapter

Watch video lessons to learn more about the Earth, the sky, and the moon. See how interrelated they are, and how that interconnectedness plays a role in observing stars, the moon, the sun, and more.

The Earth, Sky, and Moon - Chapter Summary and Learning Objectives

In this series of video lessons, the close relationship among the Earth, the sky, the sun, and the moon is explored. Gain an understanding of how brightness, motion, and color are observed, described, and measured. See how in some cases, these observed characteristics vary from actual properties. Learn more about key concepts like phases of the moon and eclipses. By the end of this chapter, you should be able to:

  • Discuss how objects in the sky are measured
  • Identify factors that affect observations of objects in the sky
  • Define terms like horizon, zenith, meridian, longitude, and latitude
  • Explain the reasons for seasons on Earth
  • Explain the phases of the moon

Video Objective
The Brightness of Stars Identify and describe the difference between subjective and objective measurements of stars' brightness.
How Stars Are Observed From Earth Explain the difference between how stars are observed from Earth and how they're actually distributed through space.
Features of the Local Sky: Horizon, Zenith & Meridian Define the terms horizon, zenith, and meridian, and discuss how they're used to talk about the observed placement of objects in the sky.
How the Sky Changes With Latitude & Longitude Define latitude and longitude, and discuss how changes in latitude and longitude affect the way stars are observed from Earth.
Measuring Objects in the Sky Explain how these objects are measured; define arcminutes and arcseconds.
Estimating the Size of Astronomical Objects Describe how the size of an object is ascertained. Explain the differences in measuring very small and very large objects.
The Four Seasons on Earth Identify seasons; explain why they exist and how they vary across Earth.
Why the Sun Changes Color Explain the changing color of the sun as it's observed rising, overhead, and setting.
Formation of the Moon: Theories Explain the theories of how the moon came to be.
Lunar Geology Describe the geology of Earth's moon.
The Atmosphere of the Moon Describe the atmosphere of Earth's moon.
What Causes the Phases of the Moon? Explain why the moon looks different over the course of a month and what causes these changes.
How the Moon Rises & Sets Identify the reasons for the moon's 'rising' and 'setting,' and explain how predictions can be made about where the moon will be at a certain time.
The Solar & Lunar Eclipse Describe two kinds of eclipses, and discuss why eclipses are important in astronomy.

15 Lessons in Chapter 21: The Earth, Sky, and Moon
Test your knowledge with a 30-question chapter practice test
Measuring Objects in the Sky: Angular Size & Distance

1. Measuring Objects in the Sky: Angular Size & Distance

Objects are measured in the sky using things like angular size and distance. Explore the celestial sphere, angles, degrees, angular distance, and size, and learn a neat trick for measuring objects in the sky.

Important Points on the Celestial Sphere

2. Important Points on the Celestial Sphere

The imaginary celestial sphere surrounding Earth is a reference tool that allows for the locations of objects in the sky to be located. Learn about the important points on the celestial sphere, including the horizon, zenith, nadir, equator, the North and South poles, and the meridian.

The Cycle of the Seasons in Astronomy

3. The Cycle of the Seasons in Astronomy

Explore astronomy's cycle of the seasons to understand Earth's seasons. Examine the ecliptic and celestial equator, the vernal equinox and summer solstice, the autumnal equinox and summer solstice, and perihelion and aphelion.

Geography of the Four Seasons

4. Geography of the Four Seasons

The geography of the four seasons is affected by the earth's rotation. Learn about the differences in seasons as affected by the earth's axis and rotation, and examine the earth's solstice between hemispheres.

The Horizon Coordinate System

5. The Horizon Coordinate System

The horizon system is used to find objects in the sky and determine their positioning. Learn more about the horizon coordinate system, the celestial horizon, altitudes and azimuth, and more on limitations.

The Equatorial Coordinate System

6. The Equatorial Coordinate System

The equatorial coordinate system is a method of identifying sections of the sky using declination (angle from equator) and right ascension (angle from vernal equinox). Learn the use of this system compared to longitude and latitude on the earth's surface.

What is Precession?

7. What is Precession?

The change in direction of Earth's axis of rotation is known as precession and it can affect the state of the planet. Learn more on recognizing the work of Hipparchus, compare revolution and rotation, and discuss the process and consequences of precession.

Lunar Eclipse: Definition & Types

8. Lunar Eclipse: Definition & Types

A lunar eclipse occurs when the moon darkens as it moves into the Earth's shadow and the two align with the sun. Explore the definition and types of lunar eclipses, such as partial and total lunar eclipse, and understand the significance of Earth's umbra and penumbra.

What Is a Solar Eclipse?

9. What Is a Solar Eclipse?

A solar eclipse occurs when the moon is between the Sun and the Earth, blocking the sunlight and casting a shadow on Earth. Learn how a solar eclipse is possible, explore partial and total solar eclipses, and discover the effects of a solar eclipse.

Annular Eclipse: The Changing Size of the Moon

10. Annular Eclipse: The Changing Size of the Moon

The annular eclipse is a type of solar eclipse that involves the visibility of the sun's photosphere as a bright ring around the moon. Explore a comparison of sun and moon size, the changing size of the moon, types of solar eclipses, and why annular eclipses occur.

How Can We Predict An Eclipse?

11. How Can We Predict An Eclipse?

Thanks to consistent lunar and solar cycles, ancient and modern astronomers have been able to predict eclipses. Learn about lunar and solar orbits, explore how we can predict an eclipse, and discover the Saros cycle.

Why the Sun Changes Color

12. Why the Sun Changes Color

The sun changes color based on our perception and the position of the sun at a given time. Explore the changing colors of the sun, wavelengths of light, and how they determine color, prisms, and the setting sun.

Magnetosphere: Definition & Facts

13. Magnetosphere: Definition & Facts

The magnetosphere is the furthest outside part of the earth's atmosphere. Explore the definition and facts about the magnetosphere and learn about the Van Allen belts, magnetopause, magnetotail, bow shock, and the aurorae.

How Gravity, the Moon & the Sun Influence Tides

14. How Gravity, the Moon & the Sun Influence Tides

Earth is connected through it's gravitational pull and chemical reactions from the moon and sun, which also influences the oceans. Learn more about these elements and how gravity also affects tides.

Tidal Friction: Effects on Earth & the Moon

15. Tidal Friction: Effects on Earth & the Moon

The moon has a major effect on the tides of the seas on Earth because of tidal bulges that create tidal friction. Learn more about tidal friction, how the moon slows down the Earth, and the Earth's effects on lunar tides.

Chapter Practice Exam
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Practice Final Exam
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