Test: Earth as a Planet - Class 9 MCQ

The terms "Blue Planet" and "Watery Planet" emphasize that about 71% of Earth's surface is covered by water. This vast presence of water is crucial for supporting life and influencing global ecosystems and climates.

Approximately 71% of Earth's surface is covered by water, which is why it is often referred to as the "Blue Planet." Water plays a critical role in supporting life and regulating climate.

The average distance from Earth to the Sun is about 150 million kilometers. This distance allows Earth to maintain an optimal temperature conducive to supporting life.

The Moon is Earth's only natural satellite. It plays a significant role in influencing tides and has been a focal point in human exploration and study of celestial bodies.

Aryabhatta was one of the earliest astronomers to suggest that the Earth is spherical. His contributions to astronomy laid foundational ideas that influenced later scientific thought about the structure of our planet.

Circumnavigation refers to the act of traveling all the way around the Earth, typically by sailing or flying. This concept was famously demonstrated by Magellan's expedition, which highlighted the spherical nature of our planet.

Eratosthenes was the first to calculate Earth's circumference using measurements of shadows in different locations. His method was innovative for its time and provided a surprisingly accurate estimate.

Shadows cast by sticks vary in length and angle due to the curvature of the Earth. On a flat surface, shadows would be consistent, but the spherical shape of Earth leads to differences based on position relative to the Sun.

Magellan's circumnavigation of the globe demonstrated that the Earth has no edges, as he traveled west and returned to his starting point. This journey provided practical evidence of Earth's spherical nature.

As one moves north or south on Earth, different constellations become visible. This phenomenon, where known constellations shift and new ones appear, supports the concept of a spherical Earth, as this wouldn't occur on a flat surface.

Earth's rotation is the primary reason for varying time zones. As the Earth rotates on its axis, different areas receive sunlight at different times, leading to the establishment of time zones around the globe.

A "geoid" refers to the shape of Earth, which resembles an oblate spheroid due to its rotation. This term emphasizes the distinct, Earth-like shape influenced by gravity and rotation.

The ozone layer absorbs harmful ultraviolet radiation from the Sun, protecting living organisms on Earth from its damaging effects. This protective layer is crucial for maintaining life and health on the planet.

The Bedford Level Experiment involved placing three poles of equal height 5 km apart in a canal. The experiment's results aligned with a curved surface, providing evidence for Earth's spherical shape.

Earth's average diameter is approximately 12,735 kilometers. This measurement helps define the size of our planet in comparison to others in the solar system, where Earth ranks as the fifth largest.