Course Overview: ERTH 105 OL S22

  • Course Title: Voyage Through The Solar System
  • Semester: Spring 2022

Moon Phases

January 2014 Moon Phases Calendar

  • Moon phases tracked throughout the month of January 2014.
    • Calendar format showing lunar visibility on specific dates.

Understanding Moon Phases

Explanation of Lunar Phases
  • Lunar phases result from the Moon's orbit around Earth.
    • The Moon completes its orbit approximately every 27.3 days.
Visual Representation of the Moon Phases
  • Half of the Moon is illuminated by the Sun.
  • The other half remains in shadow.
  • The combination of these illuminated and dark areas changes as the Moon orbits Earth.

Characteristics of Moon Phases

Cycle Duration
  • The complete cycle of Moon phases lasts 29.5 days.
Phases Categorization

  • Waxing Phase:

    • The Moon is visible during the afternoon and evening.
    • It appears to become "fuller" and rises later each successive day.

  • Waning Phase:

    • The Moon is visible late at night or in the morning.
    • It appears to become "less full" and sets later each day.
Thought Question Example
  • Scenario: Observing a half illuminated Moon at 9 a.m.
    • Possible phase choices:
    • First quarter
    • Waxing gibbous
    • Third quarter
    • Half moon

Synchronous Rotation of the Moon

Concept of Synchronous Rotation
  • Definition: The Moon rotates exactly once for every orbit it makes around Earth.
  • Outcome: Only one side of the Moon is visible from Earth at all times.

Eclipses

Causes of Eclipses

  • Eclipses occur when the Earth and Moon cast shadows.
    • An eclipse happens when either celestial body passes into the other's shadow.

Types of Lunar Eclipses

Total Lunar Eclipse
  • Occurs when the Moon passes entirely through Earth's umbra (the darkest part of the shadow).
Partial Lunar Eclipse
  • Occurs when part of the Moon passes through the umbra.
Penumbral Lunar Eclipse
  • Occurs when the Moon passes through Earth's penumbra (the lighter outer part of the shadow).
Characteristics of Lunar Eclipses
  • Only possible during a full moon.
  • Three types: Penumbral, partial, and total.

Types of Solar Eclipses

Total Solar Eclipse
  • Occurs in a small central region where the Moon completely covers the Sun's disk.
Partial Solar Eclipse
  • Occurs in the lighter areas surrounding the total eclipse.
Annular Solar Eclipse
  • Occurs when the Moon's umbral shadow does not reach Earth; a ring of sunlight is visible around the Moon.
Diagram Explanation
  • Visuals illustrating the shadow cast by the Moon on Earth during the solar eclipses.
    • Dark central umbra surrounded by a lighter penumbra.

Timing of Eclipses

Conditions for Solar Eclipses
  • Solar eclipses can occur only during a new moon.
    • Types of solar eclipses: Partial, total, and annular.
Why Eclipses Do Not Occur Regularly
  • The Moon's orbit is tilted 5° relative to Earth's ecliptic plane.
  • Results in approximately two eclipse seasons per year: lunar eclipses at new moon and solar eclipses at full moon.

Key Conditions for Eclipses

  • Two primary conditions must be met:
    • For a lunar eclipse, it must be a full moon.
    • For a solar eclipse, it must be a new moon.
    • Additionally, the Moon must be at or near its orbital nodes, where it crosses the ecliptic plane.

Predicting Eclipses

  • Eclipses recur according to the saros cycle, which lasts 18 years, 11 1/3 days.
    • Types and locations of eclipses may vary within this cycle.

Summary of Key Learnings

  • Moon Phases:
    • Appearances determined by the positioning of the Sun, Moon, and Earth.
  • Eclipses:
    • Lunar eclipses: Earth's shadow on the Moon.
    • Solar eclipses: Moon's shadow on Earth.
    • Occur twice a year due to the tilt of the Moon's orbit.