Introduction to the Earth

The earth was formed 4.6 billion years ago. About 1.6 billion years ago, the earth had only 9 hours of day and night, which was much faster than it is now, with about 800 days per year. By 600 million years ago, the earth had only 9 hours of day and night. The day and night have lengthened to 20 hours, and the year has shortened to 440 days. The earth is gradually slowing down its rotation, probably mainly due to the tidal gravity of the moon. It is generally believed that the formation of the earth originated from the differentiation of the solar nebula. Over 4.6 billion years, the earth has evolved from a homogeneous sphere into the current "sphere" structure. The average thickness of the earth's crust is 17 kilometers, the thickness of the mantle is about 3473 kilometers, accounting for 83.4% of the earth's volume, the temperature of the mantle is 1000-3000 degrees Celsius, the thickness of the earth's core is about 3473 kilometers, accounting for 16.3% of the earth's volume, the material is in a liquid state, and the inner core The temperature is as high as over 6000 degrees Celsius, which is about the same as the surface temperature of the sun!

From our perspective on Earth, our planet is very huge and rich, surrounded by seemingly endless air; however, from the perspective of astronauts from space, the Earth is just a thin sphere. , surrounded by a thin layer of atmosphere that seemed to disperse with a single blow. To a space traveler, the blue seas, brown or green land and white clouds of the Earth in the deep dark space are extremely eye-catching.

The Earth is the third planet from the Sun, at a distance of 150 million kilometers (93.2 million miles). The Earth's orbit around the sun lasts 365.256 Earth days, and its rotation lasts 23.9345 hours. Earth has a diameter of 12,756 kilometers (7,973 miles), which is only a few hundred kilometers larger than Venus. Our atmosphere is composed of 78% nitrogen, 21% oxygen and 1% other components.

The Earth is the only planet in the solar system inhabited by life. Its rapid spin and hot nickel-iron core generate enough magnetic fields to work with the atmosphere to protect us from radiation from the sun and other planets. The atmosphere also protects us from meteors, most of which burn up before reaching the Earth's surface.

From the results of many interstellar journeys, we have a deeper understanding of our planet. Explorer 1, the first artificial satellite in the United States, discovered an area of ??intense radiation now known as the Van Allen radiation belts, a layer of air composed of fast-moving electrons captured by the equatorial ring geomagnetic field. Information from other satellites shows that the geomagnetic field is distorted into a teardrop shape by the solar wind. We also learned that the thin upper atmosphere, which we thought was peaceful and stationary, is actually very active—expanding during the day and contracting at night. Due to the influence of solar activity, the upper atmosphere causes changes in the earth's weather and climate.

In addition to affecting the Earth's weather conditions, solar activity also causes strange visual phenomena in the atmosphere. When electrons from the solar wind are captured by the Earth's magnetic field, they combine with air molecules in the Earth's two-pole atmosphere. These air molecules then emit light, creating an aurora.

Earth data

Mass (kilogram) 5.976e24

Equatorial radius (kilometer) 6,378.14

Equatorial circumference 40075.7 kilometers< /p>

Surface area 510 million square kilometers

Polar radius 6356.75 kilometers

Equatorial radius ratio (Earth = 1) 1.0000e+00

Average density (g/cm3) 5.515

Perihelion distance (around January 3 every year) 147,100,000 kilometers

Aphelion distance (every July Around 4 days) 152,100,000 kilometers

The average distance from the sun is 149,600,000 kilometers (one astronomical unit)

Rotation period (day) 0.99727

Rotation period 23 hours, 56 minutes and 1.09 seconds (average solar time)

Revolution period (days) 365.256

Revolution distance 940 million kilometers

Average revolution period ( Kilometers/second) 29.79

Gravity acceleration 1 G (9.8 meters/second)

Revolutional eccentricity 0.0167

Yellow-red intersection angle (degree) 23.45

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Orbital inclination angle (degree) 0.000

Equatorial separation velocity (km/s) 11.18

Equatorial surface gravity acceleration (m/square second) 9.78 < /p>

Visual geometric albedo 0.37

Average surface temperature 15°C

Atmospheric pressure (bar) 1.013

Atmospheric composition

Nitrogen

Oxygen

Others

77%

21%

2%