Wei Zi science blogger

The earth is a planet that is neither too big nor too small. But it is our home planet, where all life is located, and where we can observe the whole universe.

Illustration: Digital Art of the Earth.

Astronomers and geologists learn about the earth and its planetary families by studying other worlds. Now they think that the planet is formed by the ring of rotating debris left by the birth of the sun.

The shape of the earth

The earth is not a perfect sphere, its poles are flat. Between the two poles, the diameter of the earth is 12700 km. And near the equator, its diameter is 12750 km.

Illustration: The shape of the earth.

Geodesy is a subject that studies the shape of the earth. Modern geologists know the shape of the earth from photos taken in space. But people came to this conclusion a long time ago. For example, people noticed that ships in the distance seemed to have fallen below the horizon. Early astronomers observed the motion of the solar eclipse: the earth cast a curved shadow on the moon. So the earth is round.

Mass and density

The mass of an object tells us how much matter it contains. 1735, mathematician pierre bouguer estimated the mass of the earth. Today scientists know that the earth weighs 6.59× 10 2 1 ton (5.98×102/mt). To calculate its density, scientists divide the mass of the earth by its volume. The weight of air, water and rocks on the earth is about 5.5 times that of the same amount of water. This makes the earth the densest of all planets.

Gravity and magnetism

Gravity is a force that pulls everything to the center of the earth. The earth is also a huge magnet. It has the North Pole and the South Pole. The magnetic poles are not in the same place as the poles of the earth. Compasses work because of the magnetism of the earth.

Three parts of the earth

The earth is made up of air, water and solid land. Scientists call it the atmosphere, hydrosphere and lithosphere. These terms are derived from Greek roots. Atmos stands for steam, Hydro stands for water and Lithos stands for stone.

atmosphere

The earth is surrounded by a layer of gas called the atmosphere. This protects it from deadly radiation and meteors. The atmosphere also acts like a blanket to keep the temperature of the earth stable. This layer consists of 2 1% oxygen, 78% nitrogen and 1% other gases. It also contains dust and water vapor.

steam

When you look at the earth from space, it may be called the blue planet. Three quarters of its surface is covered with water. This is the hydrosphere. The earth is the only known planet with liquid water. Oceans, lakes and rivers are full of plants and animals. The hydrosphere provides food, fertilizer and industrial raw materials. The ocean produces salt and many other important chemicals.

lithosphere

The lithosphere is the solid part of the earth. It has a solid outer mantle about 1740 miles (2,800 kilometers) thick. The earth's crust consists of rocks and soil. It forms the top 25 miles (40 kilometers) of the mantle. Geophysicists use seismic waves to understand the interior of the earth. Below the mantle is the core, about 4,400 miles (7 100 km) wide. The core has a solid inner core and a melted outer core.

The age of the earth

Fossils convince scientists that the earth is very old. Now scientists use radioactive elements to measure the age of the earth. By knowing how long it takes for these rocks to decay, geologists can calculate the age of the rocks or minerals in which they are located. Several radioactive elements or isotopes are often used, the most famous of which is carbon 14.

Scientists found that the oldest known rock was formed 4.2 billion years ago. They think that the earth itself is about 4.6 billion years old.

earth rotation

People in ancient times thought that the earth was stationary. They think that the sun, moon and stars all revolve around us. Now I

Scientists know that the earth revolves around its axis. The earth rotates once every 23 hours, 56 minutes and 4.09 seconds. 185 1 year, French scientist Jean-Bernard-Lyon Foucault proved this with a pendulum. He tied a heavy and sharp weight to a long rope hanging from the high ceiling, and there was a layer of sand under the hanging object. When the pendulum swings back and forth, the tip of this heavy object will mark its movement on the sand on the floor. These marks point in different directions, and the Foucault pendulum shows that the earth must be turning.

It is the rotation of the earth that causes day and night. It makes the airflow turn right in the northern hemisphere and left in the southern hemisphere. This phenomenon is called Coriolis effect.

The revolution of the earth

When the earth rotates, it also goes around the sun. The whole process lasted 365 days, 6 hours and 9 minutes 10 second, which was called the sidereal year. The earth's orbit around the sun is a flattened ellipse, so the distance between the earth and the sun will change slightly in a year. The closest place to the sun is called perihelion, which occurs at the beginning of 1 month. The farthest place from the sun is called apohelion, which occurs in early July. The earth is 4.8 million kilometers closer to the sun at perihelion than at aphelion.

The earth axis is inclined about 23.5 degrees with respect to the track line. In some orbits, each hemisphere is biased towards the sun, which is summer. When the hemisphere deviates from the sun, winter comes. The speed of the earth's orbit is about 30 kilometers per second. It moves fastest at perihelion. The earth also moves with the sun. The sun pulls the solar system across the sky on its own journey. It revolves around the center of the Milky Way every 200 million years. This is called the year of the universe. The speed of this journey is about 230 kilometers per second.

precession of the equinoxes

The earth is like a tilted top, swinging around its axis. This is called precession. Precession is mainly caused by gravity when the moon orbits the earth. It takes about 25,800 years to complete a swing.

When the earth swings, its axis points to different positions in space. Today, the earth's axis points to Polaris. The position of the North Pole star will change after many centuries. When the Egyptians built the pyramids, the star on the right was Polaris. By 14000, Vega will become the North Star. Polaris will return to that position after a complete swing.

reference data

1. Wikipedia

2. Astronomical terminology

3. Time Now-Touch the Concave

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