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Earth, Moon, and the Sun - Eclipses

Grade 7CBSE

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

🔑Concepts

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Rectilinear Propagation of Light: Light travels in straight lines. This property is responsible for the formation of shadows, which leads to eclipses.

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Shadow Components: A shadow consists of two parts: the Umbra (the darkest, central part where light is completely blocked) and the Penumbra (the outer, lighter part where light is partially blocked).

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Solar Eclipse: Occurs when the Moon passes between the Sun and the Earth (Sun→Moon→EarthSun \rightarrow Moon \rightarrow Earth), casting a shadow on the Earth. This happens only on a New Moon day (AmavasyaAmavasya).

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Lunar Eclipse: Occurs when the Earth passes between the Sun and the Moon (Sun→Earth→MoonSun \rightarrow Earth \rightarrow Moon), casting its shadow on the Moon. This happens only on a Full Moon day (PurnimaPurnima).

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Orbital Tilt: Eclipses do not occur every month because the Moon's orbit is tilted at an angle of approximately 5∘5^\circ relative to the Earth's orbit around the Sun.

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Corona: During a total solar eclipse, the Sun's outer atmosphere, known as the 'Corona', becomes visible to the naked eye.

📐Formulae

Sun — Moon — Earth=Solar EclipseSun \text{ --- } Moon \text{ --- } Earth = \text{Solar Eclipse}

Sun — Earth — Moon=Lunar EclipseSun \text{ --- } Earth \text{ --- } Moon = \text{Lunar Eclipse}

Tilt of Moon’s Orbit≈5∘\text{Tilt of Moon's Orbit} \approx 5^\circ

Total Duration=Partial Phase Time+Totality Time\text{Total Duration} = \text{Partial Phase Time} + \text{Totality Time}

💡Examples

Problem 1:

During a solar eclipse observation, the total duration from the start of the partial eclipse to the end was recorded as 480480 seconds. If the period of 'Totality' (the sun being completely covered) lasted for 155155 seconds, calculate the total duration of the partial phases using vertical subtraction.

Solution:

To find the partial phase duration, we subtract the totality time from the total duration:

480−155325\begin{array}{r} 480 \\ - 155 \\ \hline 325 \end{array}

The duration of the partial phases is 325325 seconds.

Explanation:

In an eclipse event, the total time is the sum of the time the observer spends in the penumbra (partial eclipse) and the umbra (total eclipse). By subtracting the umbra time from the total time, we find the penumbra time.

Problem 2:

Why doesn't a lunar eclipse occur on every Full Moon day?

Solution:

A lunar eclipse requires the Sun, Earth, and Moon to be in a perfect straight line. However, the Moon's orbital plane is tilted at an angle of 5∘5^\circ to the Earth's orbital plane. Therefore, the Moon usually passes above or below the Earth's shadow during a Full Moon.

Explanation:

The 5∘5^\circ tilt means the three celestial bodies only align perfectly at specific points called 'nodes' where the orbits intersect.