krit.club logo

Earth and Space - The Moon and its phases

Grade 4IGCSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

•

The Moon is Earth's only natural satellite, orbiting at an average distance of approximately 384,400 km384,400 \text{ km}.

•

The Moon does not produce its own light; we see it because it reflects light from the Sun. This property is known as its albedo, which is approximately 0.120.12.

•

A complete cycle of Moon phases, from one New Moon to the next, takes about 29.529.5 days. This is known as a synodic month.

•

The phases of the Moon occur because as the Moon orbits Earth, different portions of its sunlit side are visible to us. The main phases are: New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, Third (Last) Quarter, and Waning Crescent.

•

The term 'Waxing' refers to the illuminated part of the Moon growing larger in appearance (moving toward Full Moon), while 'Waning' refers to it growing smaller (moving toward New Moon).

•

The Moon's gravity is much weaker than Earth's, being approximately 16\frac{1}{6} or 16.6%16.6\% of Earth's gravity (gMoon≈1.62 m/s2g_{Moon} \approx 1.62 \text{ m/s}^2).

📐Formulae

Lunar Cycle≈29.5 days\text{Lunar Cycle} \approx 29.5 \text{ days}

RMoon≈14REarthR_{Moon} \approx \frac{1}{4} R_{Earth}

gMoon≈16gEarthg_{Moon} \approx \frac{1}{6} g_{Earth}

Distance≈3.84×105 km\text{Distance} \approx 3.84 \times 10^5 \text{ km}

💡Examples

Problem 1:

If a Full Moon is observed on the 1st1^{st} of the month, approximately on what day would you expect to see the next Full Moon?

Solution:

The next Full Moon would occur around the 30th30^{th} or 31st31^{st} of the month.

Explanation:

Because a full lunar cycle takes approximately 29.529.5 days, you add 29.529.5 to the starting date. 1+29.5=30.51 + 29.5 = 30.5, which falls at the end of the month.

Problem 2:

An astronaut weighs 600 N600 \text{ N} on Earth. Calculate their approximate weight on the Moon using the gravity ratio 16\frac{1}{6}.

Solution:

WeightMoon=600 N×16=100 NWeight_{Moon} = 600 \text{ N} \times \frac{1}{6} = 100 \text{ N}

Explanation:

Since the Moon's gravity is 16\frac{1}{6} of Earth's, any object's weight is divided by 66 when measured on the Moon's surface.

Problem 3:

Identify the phase of the Moon when it is positioned directly between the Earth and the Sun.

Solution:

New Moon

Explanation:

During the New Moon phase, the side of the Moon facing Earth receives no direct sunlight, and the Moon is located in the same direction as the Sun from our perspective.