Earth: Definition, Size, Composition, Temperature, Mass, & Facts

Introduction

• Earth is the third planet from the Sun and fifth largest in the solar system.
• Unique for harboring life in its near-surface environments.
• Name derived from Old English and Germanic, not mythology.
• Part of the observable universe, which humans can observe with technology.

Historical Perspective

• Copernican revolution (16th century) shifted view to Earth as a planet.
• Galileo's telescope further confirmed Earth's spherical nature.
• Space exploration in the 20th century visually confirmed Earth's roundness.
• Earth viewed as a bright, bluish planet with atmospheric features if observed from space.

Physical Characteristics

• Earth's surface is divided into seven continents and five oceans.
• Comprised of concentric layers: core, mantle, crust, hydrosphere, atmosphere, and magnetosphere.
• Detailed knowledge of Earth provides insights into planetary cooling, magnetic field generation, and energy release.

Orbital and Rotational Data

• Mean distance from the Sun: about 149.6 million km.
• Orbits the Sun in 365.25 days; rotation period is approximately 23.9345 hours.
• Axis tilt: 23.44 degrees, resulting in seasonal changes.
• Earth's orbit is relatively circular compared to other planets.

Size and Mass

• Equatorial radius: 6,378 km; largest of terrestrial planets, smaller than gas giants.
• Mass: 5.972 × 10^24 kg.
• Has one natural satellite, the Moon, considered significant in size.

Gravitational and Tidal Forces

• Earth exerts gravitational force affecting its orbit and causes tides.
• Moon's gravitational force also generates tides on Earth.
• Tidal forces slow Earth's rotation and influence the Moon's orbit.

Atmospheric and Surface Data

• Atmosphere composed of nitrogen (78%), oxygen (21%), argon, carbon dioxide, and water vapor.
• Mean surface temperature: 288 K (15°C or 59°F).
• Atmospheric pressure: 1 bar.

Significance of Atmosphere and Hydrosphere

• Essential for life, involving distribution and recycling of gases and liquids.
• Solar energy plays a crucial role in sustaining life.