Problem 8 - Astronomy: At Play in the Cosmos

Question

Which statement about Moon phases is true? a. In waxing phases, the lit portion of the Moon faces the eastern horizon. b. The new Moon has its whole face illuminated as seen from Earth. c. The Moon rises at sunset every day. d. The waning gibbous phase follows the full Moon. e. In waning phases, the lit portion of the Moon faces the western horizon.

Step-by-Step Solution

Answer

Statements d and e are true.

Step 1: Understand the Phases of the Moon

The Moon goes through different phases in a lunar month: new Moon, waxing crescent, first quarter, waxing gibbous, full Moon, waning gibbous, last quarter, and waning crescent. These phases are a result of the Moon's position relative to the Earth and Sun.

Step 2: Examine Each Statement

Analyze each statement to understand what it claims and compare it with the known facts about the Moon's phases. - **Statement a:** Claims lit portion faces east during waxing. Instead, the lit portion faces west. - **Statement b:** Claims new Moon is fully lit, but during a new Moon, the side facing Earth is not illuminated. - **Statement c:** Suggests that the Moon rises at sunset every day, which is incorrect; only during a full Moon does the Moon rise at sunset. - **Statement d:** Claims the waning gibbous phase follows the full Moon. This is true; after the full Moon, the visible portion starts decreasing, entering the waning gibbous phase. - **Statement e:** Claims lit portion faces west in waning phases, which is correct.

Step 3: Verify Correctness of Each Statement

Now check which statements align with reality: - Statement a is incorrect. - Statement b is incorrect. - Statement c is incorrect. - Statement d is correct. - Statement e is also correct. Therefore, Statements d and e are true.

Step 4: Finalize the Answer

Since the problem asks for the true statements about Moon phases, identify statements d and e as true.

Key Concepts

Lunar Month

A lunar month is the time it takes for the Moon to complete a full cycle of its phases, passing through each distinct phase before returning to its starting point. This cycle lasts approximately 29.5 days. The phases that mark this month-long journey include:

• New Moon: The Moon is positioned between Earth and the Sun, making it nearly invisible from Earth.
• Waxing Crescent: A sliver of the Moon becomes visible, with illumination increasing each day.
• First Quarter: Half of the Moon is illuminated and visible.
• Waxing Gibbous: The illuminated portion continues to grow, approaching fullness.
• Full Moon: The entire face of the Moon is illuminated.
• Waning Gibbous: After a Full Moon, the illumination begins to decrease.
• Last Quarter: Again, half of the Moon is visible, but the illuminated part is shrinking.
• Waning Crescent: The visible part continues to diminish until it returns to a New Moon.

Understanding this cycle is crucial when studying how the Moon appears differently throughout the month.

Waxing and Waning Phases

The terms "waxing" and "waning" describe the changes in the visible area of the Moon's surface that is illuminated by the Sun:
- Waxing Phases:

• "Waxing" means increasing, so during these phases, the visible portion of the Moon's surface is getting larger.
• This occurs after the New Moon and before the Full Moon. The progression goes through Waxing Crescent, First Quarter, and Waxing Gibbous.
• The lit portion of the Moon is on the right side when facing it from Earth, which is why it appears to "grow" nightly.

- Waning Phases:

• "Waning" means decreasing, indicating that the visible illuminated part of the Moon is shrinking.
• This starts after the Full Moon as it moves through Waning Gibbous, Last Quarter, and finally Waning Crescent back to New Moon.
• During waning phases, the illuminated portion decreases from the left side.

These changing views result from the interplay of light and shadow as the Moon orbits Earth.

Moon's Position Relative to Earth and Sun

The fascinating phenomena of Moon phases are primarily due to its orbit around Earth, combined with the Sun's light, creating various visible shapes. As the Moon circles Earth every month, different amounts of its sunlit half are visible from our vantage point:

• During a New Moon, the Moon is nearly directly between the Earth and Sun, causing the side facing Earth to be dark and invisible.
• Conversely, during a Full Moon, Earth is between the Sun and the Moon, allowing the entire sunlit side to be visible.
• In the First and Last Quarters, the angles form a right angle with the Earth, half of the Moon is lit.

Understanding this relationship explains how observers on Earth witness different phases. The changing angles, from the Aesthetic First Quarter to the vastness of Full Moon's illumination, remind us of the intricate cosmic dance between these celestial bodies.