5.4. Planets of the Solar System: Earth: Our home in space

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5.4. Planets of the Solar System: Earth: Our home in space

Earth, our home planet, is the third closest planet to the sun and the only celestial body known to harbor life. This chapter of the "Learn Astronomy: Complete Course to Learn About Outer Space" course will dive deep into exploring Earth, its unique features, its relationship to the sun and moon, and how it fits into the larger solar system.

Characteristics of the Earth

Earth is the largest of the four rocky planets in the solar system, with a diameter of about 12,742 kilometers. Its surface is mainly made up of water (71%) and land (29%), with an atmosphere made up mainly of nitrogen (78%) and oxygen (21%). Earth also has an ozone layer that protects life on the surface from the sun's harmful ultraviolet rays.

One of Earth's most distinctive features is the presence of life. Life on Earth is diverse and complex, ranging from single-celled organisms to complex multicellular life forms. The presence of life on Earth is possible thanks to its distance from the sun, which allows for a global average temperature that supports liquid water - a key ingredient for life as we know it.

The Earth and the Sun

The Earth orbits the sun at an average distance of about 150 million kilometers. This distance is often referred to as an Astronomical Unit (AU). The Earth takes about 365.25 days to complete one orbit around the sun, a period of time we define as one year.

The rotation of the Earth on its axis (a process that takes about 24 hours) and its orbit around the sun are responsible for the daily and seasonal variations in light and temperature on the Earth's surface. The tilt of Earth's axis of about 23.5 degrees relative to the plane of its orbit is what causes the seasons.

The Earth and the Moon

The Earth has a natural satellite, the Moon. The Moon is the fifth largest satellite in the solar system and orbits the Earth at an average distance of about 384,400 kilometers. The presence of the Moon has a significant impact on the Earth, causing ocean tides and stabilizing the tilt of the Earth's axis.

Earth in the Solar System

Earth is one of the eight planets in the solar system. It is the third closest planet to the sun, located between Venus and Mars. Earth is one of the four rocky or terrestrial planets in the solar system, along with Mercury, Venus and Mars. These planets are significantly smaller and denser than the gas giants of the outer solar system: Jupiter, Saturn, Uranus and Neptune.

In short, Earth is a unique and complex planet that offers ideal conditions for life. Its relationship to the sun and moon, as well as its position in the solar system, plays a crucial role in its characteristics and conditions. By exploring Earth, we can begin to better understand our place in the cosmos and appreciate the beauty and complexity of the world we live in.

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225.5. Planets of the Solar System: Mars: The red planet