What Is Earth?
Earth is our home planet, believed to have formed around 4.5 billion years ago alongside the rest of the solar system. It is the fifth-largest planet in the solar system, with a diameter of approximately 8,000 miles, and is the third-closest planet to the Sun, situated about 93 million miles away on average.
The "Goldilocks Planet"
Earth is often referred to as the "Goldilocks planet" because its conditions are just right for life to exist. It is warm but not too warm, and it has water but not too much. Liquid water, essential for life, is abundant on Earth, making it unique among known planets.
Earth from Space
From space, Earth appears as a blue marble with white swirls and areas of brown, yellow, green, and white. The blue represents water, which covers about 71% of Earth's surface. The white swirls are clouds, the brown and green areas are land, and the white regions are ice and snow.
Geography and Climate
The Equator is an imaginary line dividing Earth into the Northern and Southern Hemispheres. The Northernmost point is the North Pole, and the Southernmost point is the South Pole. Earth’s round shape has been known for over 2,000 years, proven by the ancient Greeks through shadow measurements and star positions.
Shape and Rotation
Although Earth is a sphere, it is not a perfect one. Its rotation causes a slight flattening at the poles. Earth orbits the Sun once every 365 days and spins on its axis, tilted at 23.5 degrees, every 24 hours. This tilt and rotation cause the cycle of day and night and the changing seasons.
Seasons and Hemispheres
Earth's tilt means different parts of the planet receive varying amounts of sunlight throughout the year, leading to seasonal changes. From June to August, the Northern Hemisphere experiences summer while the Southern Hemisphere has winter, and from December to February, the opposite occurs. During March to May and September to November, both hemispheres receive equal sunlight, resulting in spring and autumn.
Composition and Structure
Earth consists of land, air, water, and life. Its surface has mountains, valleys, and flat areas. The atmosphere is primarily nitrogen and oxygen, while water bodies include oceans, lakes, rivers, and ice. Life on Earth ranges from tiny microorganisms to large plants and animals. Below the surface are layers of rock and metal, with temperatures increasing towards the inner core.
NASA’s Studies of Earth
NASA studies Earth to understand its changes, using satellites to observe clouds, oceans, land, ice, and atmospheric gases. This data helps predict weather and climate, track diseases and famine, and aid in disaster response. Understanding Earth's changes helps us make better decisions for the future.
Astronomical Perspective
Earth, symbolised by ♁, is the only planet known to harbour life. Its name, derived from Old English and Germanic words for ground, is unique as it does not come from Greco-Roman mythology. Earth is part of the observable universe and has been regarded as a planet since the Copernican Revolution of the 16th century. Space exploration has provided direct visual evidence of Earth's spherical shape.
Viewed from Space
Seen from another planet, Earth appears bright and bluish due to its atmosphere and water. The polar regions are white from clouds and ice, while the oceans and desert lands show darker colours. Seasonal changes affect cloud patterns and snowcaps, visible from space.
Scientific Study of Earth
Modern instrumentation has revealed much about Earth's structure and composition, aiding in understanding planetary processes. Earth's surface is traditionally divided into seven continents and five major oceans, but it is also composed of concentric layers: the core, mantle, crust, hydrosphere, atmosphere, and magnetosphere.
Earth's Orbit and Rotation
Earth orbits the Sun in an almost circular path, completing one revolution every 365.25 days. Its rotation period is 23 hours, 56 minutes, and 4 seconds. The 23.44° tilt of Earth's axis causes seasonal variations in temperature and daylight.
Gravitational Field and Tides
Earth's gravitational field attracts objects towards its centre, causing tides in both the solid body of the Moon and Earth's oceans. The Sun and the Moon's gravitational forces cause the tides, affecting Earth's rotation and the Moon's orbit.
Conclusion
Understanding Earth and its changes is crucial for making informed decisions about our planet's future. NASA's ongoing studies and observations continue to provide valuable insights into the dynamic systems that make Earth unique.
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