Moon, Lunar Phases, and Eclipses

Moon

• Today's topics include the moon, its different phases, rise and set times, and eclipses (both lunar and solar).

Cycles of the Moon

• Sidereal and synodic periods are important concepts.
  • Sidereal Period: $27.32$ days
  • Synodic Period: $29.53$ days

The Phases of the Moon (1)

• The Moon orbits Earth in a sidereal period of $27.32$ days. This is the time it takes for the Moon to return to the same position relative to the stars.

The Phases of the Moon (2)

• The Moon’s synodic period, which is the time it takes to reach the same position relative to the Sun (i.e., the same lunar phase), is $29.53$ days (approximately 1 month).
• The difference between sidereal and synodic periods is due to Earth's orbit around the Sun, which causes the direction toward the Sun to change.
• Lunar Phases:
  • New Moon
  • Waxing Crescent
  • First Quarter
  • Waxing Gibbous
  • Full Moon
  • Waning Gibbous
  • Third Quarter
  • Waning Crescent

Lecture Tutorial: Predicting Moon Phases pp. 85-87

• Instructions for a lecture tutorial involving predicting moon phases.
  • Work with partners.
  • Read instructions and questions carefully.
  • Discuss concepts and answers.
  • Come to a consensus.
  • Write clear explanations.
  • Ask another group if stuck.
  • Ask for help if really stuck.
• Phases and rise/set times:
  • 1st Quarter
  • Full Moon
  • 3rd Quarter
  • New Moon
  • Waxing Crescent
  • Waxing Gibbous
  • Waning Gibbous
  • Waning Crescent

Eclipses

• Eclipses occur when the Earth, Moon, and Sun form a straight line.

Conditions for Eclipses (1)

• Solar Eclipse: Can only occur if the Moon passes a node near the New Moon.
• The Moon’s orbit is inclined to the ecliptic by approximately $5$ degrees.
• Lunar Eclipse: Can only occur if the Moon passes a node near the Full Moon.

Lunar Eclipses

• Earth's shadow consists of two zones:
  • Penumbra: A zone of partial shadow.
  • Umbra: A zone of full shadow.
• If the Moon passes through Earth’s full shadow (Umbra), we see a lunar eclipse.
• If the entire surface of the Moon enters the Umbra, the lunar eclipse is total.

A Total Lunar Eclipse

• A total lunar eclipse can last up to 1 hour and 40 minutes.
• During a total eclipse, the moon has a faint, red glow due to sunlight scattered in Earth’s atmosphere.

Lunar Eclipses: 2015-2024

• There are typically 1 or 2 lunar eclipses per year.

Solar Eclipses

• The Sun appears approximately as large in the sky (same angular diameter ≈ $0.5$ degrees) as the Moon.
• $≈ 0.5^o = 30'$

Solar Eclipses (II)

• When the Moon passes in front of the Sun, the Moon can cover the Sun completely, causing a total solar eclipse.

Moon Shadow on Earth

• Illustration of the moon's shadow on Earth during a solar eclipse.

Solar Eclipses: 2019-2028

• There are on average about 1 – 2 total solar eclipses per year.