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The Earth and Space - Constellations and the Moon

Grade 4CBSE

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

🔑Concepts

The Moon is the Earth's only natural satellite and is about 14\frac{1}{4} the size of the Earth.

The Moon does not have its own light; it reflects the light of the Sun. This is why we see it shining in the night sky.

The Moon takes approximately 27.327.3 days to revolve around the Earth, and the time between one full moon and the next is about 29.529.5 days.

Phases of the Moon: As the Moon orbits Earth, different parts of its sunlit surface are visible to us, creating phases such as the New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, Last Quarter, and Waning Crescent.

A constellation is a group of stars that appears to form a specific pattern or shape in the night sky, often named after animals, mythological characters, or objects.

Ursa Major (The Great Bear) is a prominent constellation that contains a group of seven bright stars called the 'Big Dipper' or 'Saptarishi'.

Orion (The Hunter) is another famous constellation visible during winters, easily identified by the three bright stars forming 'Orion's Belt'.

The Moon has no atmosphere or liquid water, and its surface is covered with deep holes called craters, formed by the impact of meteorites.

📐Formulae

gmoon16×gearthg_{moon} \approx \frac{1}{6} \times g_{earth}

Distance from Earth to Moon384,400 km\text{Distance from Earth to Moon} \approx 384,400 \text{ km}

Lunar Cycle29.5 days\text{Lunar Cycle} \approx 29.5 \text{ days}

💡Examples

Problem 1:

If an astronaut weighs 60 kg60 \text{ kg} on Earth, what would be their approximate weight on the Moon?

Solution:

The weight on the Moon would be approximately 10 kg10 \text{ kg}.

Explanation:

Gravity on the Moon is much weaker than on Earth. Using the formula Weightmoon=Weightearth×16Weight_{moon} = Weight_{earth} \times \frac{1}{6}, we calculate 60×16=10 kg60 \times \frac{1}{6} = 10 \text{ kg}.

Problem 2:

Identify the constellation often referred to as 'The Hunter' and describe its main feature.

Solution:

The constellation is Orion.

Explanation:

Orion is known as 'The Hunter'. Its most recognizable feature is the 'Belt of Orion', which consists of 33 bright stars in a straight line.

Problem 3:

Why does the Moon appear to change its shape every night?

Solution:

This happens due to the Moon's revolution around the Earth.

Explanation:

As the Moon moves around the Earth, the angle of sunlight hitting the Moon changes from our perspective. The different visible portions of the illuminated side are called the 'Phases of the Moon'.

Constellations and the Moon - Revision Notes & Key Formulas | CBSE Class 4 Science