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Earth and Space - Phases of the Moon and Eclipses

Grade 6IB

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

🔑Concepts

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The Moon is non-luminous and is seen because it reflects light from the Sun. The distance between the Earth and the Moon is approximately 3.84×105 km3.84 \times 10^5 \text{ km}.

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The Moon orbits the Earth once every 27.327.3 days (sidereal month), but the lunar cycle from New Moon to New Moon takes approximately 29.529.5 days (synodic month) due to Earth's movement around the Sun.

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Lunar phases are determined by the Moon's position relative to the Sun and Earth. The eight phases include: New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, Third Quarter, and Waning Crescent.

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A Solar Eclipse occurs when the Moon passes directly between the Sun and Earth, casting a shadow on Earth. This alignment is Sun →\rightarrow Moon →\rightarrow Earth and can only occur during a New Moon.

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A Lunar Eclipse occurs when the Earth passes directly between the Sun and the Moon, casting Earth's shadow on the Moon. This alignment is Sun →\rightarrow Earth →\rightarrow Moon and can only occur during a Full Moon.

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The Moon's orbit is tilted at an angle of approximately 5∘5^\circ relative to the Earth's orbit around the Sun (the ecliptic). This tilt prevents eclipses from occurring every single month.

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The shadow during an eclipse consists of two parts: the Umbra (the darkest, central part where the light source is completely blocked) and the Penumbra (the outer, lighter part where the light source is only partially blocked).

📐Formulae

Tsynodic≈29.5 daysT_{synodic} \approx 29.5 \text{ days}

Distance=Speed×Time\text{Distance} = \text{Speed} \times \text{Time}

θtilt≈5∘\theta_{tilt} \approx 5^\circ

💡Examples

Problem 1:

Calculate the time it takes for light to travel from the Moon to the Earth if the distance is 384,400 km384,400 \text{ km} and the speed of light is c≈3×105 km/sc \approx 3 \times 10^5 \text{ km/s}.

Solution:

t=dc=3.844×105 km3×105 km/s≈1.28 st = \frac{d}{c} = \frac{3.844 \times 10^5 \text{ km}}{3 \times 10^5 \text{ km/s}} \approx 1.28 \text{ s}

Explanation:

By applying the formula for time (t=d/vt = d/v), we find that light reflected from the Moon reaches Earth in just over one second.

Problem 2:

During which phase of the lunar cycle does a Lunar Eclipse occur, and what is the specific order of the celestial bodies?

Solution:

Phase: Full Moon; Order: Sun →\rightarrow Earth →\rightarrow Moon.

Explanation:

A lunar eclipse happens when the Earth's shadow falls on the Moon. This can only happen when the Moon is on the opposite side of the Earth from the Sun, which corresponds to the Full Moon phase.

Problem 3:

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

Solution:

1+29.52≈15.75 days1 + \frac{29.5}{2} \approx 15.75 \text{ days} (Around the 15th15^{th} or 16th16^{th} of the month).

Explanation:

A full lunar cycle is roughly 29.529.5 days. The Full Moon occurs halfway through this cycle, which is approximately 14.7514.75 days after the New Moon.

Phases of the Moon and Eclipses - Revision Notes & Key Formulas | IB Grade 6 Science