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3: Motions of the Moon, Sun, and Stars

Last updated

Jul 23, 2025
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- 2.11: The Mathematical Finish- Newton
- 3.1: Motions of Objects

Lumen Learning
Lumen Learning

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The Earth,
Though, in comparison of Heaven, so small
Nor glistering, may of solid good contain
More plenty than the Sun that barren shines.

John Milton,
Paradise Lost, 1665

Learning Objectives

Upon completion of this module, the student will be able to:

Define motions of objects, including rotation, revolution, and precession
Identify parts of the points on the Celestial Sphere, such as the celestial poles, meridian, zenith, celestial equator, and ecliptic
Identify measurement systems used by astronomers
Explain why we experience seasons, and the descriptions used to discuss seasons
Explain why the Moon goes through its phases, and the terminology used to explain the phases of the Moon
Identify types of eclipses
Explain why eclipses occur

This module will overview movements of Earth, the Moon, and other astronomical bodies and the effects these movements have on what we observe from here on Earth.

3.1: Motions of Objects
This page explains the two main motions of celestial bodies: rotation and revolution. Rotation is the spinning of an object around its axis, with Earth completing this every 24 hours and Jupiter in about 10 hours, resulting in day and night. Revolution refers to an object's orbit around another, with Earth taking 365.24 days to revolve around the Sun, while Jupiter requires about 11.86 Earth years. These motions change our perspective of the night sky over time.
3.2: Our Night Sky
This page explains the concept of the Celestial Sphere, an imaginary sphere around the Earth that depicts the movement of celestial objects. It outlines how directions are determined using cardinal points and coordinates, highlights the significance of the North and South Celestial Poles, and discusses the Local Sky variations.
3.3: The Sun and the Moon
This page discusses the movement of the Sun, Moon, and planets along the Ecliptic on the Celestial Sphere and introduces the Zodiac, consisting of 12 constellations plus one additional. It explains that astronomers measure sizes and distances in angular measurements, noting that the Sun and Moon appear to span approximately ½ degree or 30 arcminutes from Earth's view, despite their actual sizes being different.
3.4: Seasons and Seasonal Changes
This page discusses seasons as a result of Earth's axial tilt of about 23.5 degrees, influencing weather and daylight changes during its orbit. It clarifies misconceptions about the sun's distance and introduces key terms like solstices and equinoxes that denote daylight changes. Furthermore, it explains how Earth's axial orientation changes over time due to precession, affecting seasonal timing over a 26,000-year cycle, with minor fluctuations caused by nutation.
3.5: The Moon in our Skies
This page explores the Moon's orbit around Earth, its phases, and visibility. It distinguishes between Sidereal and Synodic months, noting that one side of the Moon always faces Earth. The phases, including crescent and gibbous, are defined by illumination and position. It also discusses daytime visibility, the variable distance between Earth and the Moon, and cultural references to the Moon in literature and scripture.
3.6: Eclipses
This page explains eclipses, including lunar and solar types. A lunar eclipse happens when Earth is between the Sun and the Moon, creating color variations due to atmospheric effects. In a solar eclipse, the Moon blocks the Sun at new moon, with total solar eclipses causing a day-to-night transition and showcasing phenomena like the Diamond Ring and Baily's Beads. Historically, eclipses have sparked myths and evoked feelings of fear or awe in people.

Learning Objectives

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