How many colors does the earth have from the perspective of space?

The brilliant light at the edge of the earth

What is the most beautiful scene in the vast universe? Astronaut Chen Dong answered: "My favorite is the bright atmospheric glow outside the Earth, which flickers at the edge of the Earth and appears golden, blue or purple. Although I have seen it many times, every time I am shocked and very beautiful."

In the vast space of the universe, astronauts can enjoy a visual feast of sunrise and sunset every 90 minutes. As the spacecraft flies at high speed, the rising and setting of the sun is particularly spectacular, like a blazing fireball leaping in the sky. Unlike on Earth, there is no distant horizon or coastline in space as a reference for sunrise, and there is no scattering and refraction of the atmosphere. Therefore, the sunrise scene in space presents a unique beauty: before the sun is about to rise, the edge of the earth is surrounded by a bright white light, as if the edge of the earth is inlaid with a dazzling golden edge.

Some children may ask again, why can we see these beautiful colors? Light is an electromagnetic wave, and the human eye can only perceive light with a wavelength of 380 to 780 nanometers, which is visible light. When these light waves break into your eyeballs, they begin to stimulate the visual receptor cells, causing them to excitedly send signals to the brain. The brain then turns the signals into colorful delicacies, allowing us to taste the colorful world. Light waves of different wavelengths are like different seasonings, allowing the brain to distinguish various colors. So, next time you admire the beautiful scenery, remember to thank your brain and those hard-working "taste buds" cells!

Blue Earth

Why is the Earth a blue planet?

Soviet cosmonaut Yuri Gagarin achieved a major breakthrough in human history by becoming the first Earth resident to travel into space. Gagarin had a profound description of the scene in space: although space was pitch black, the Earth appeared blue and extremely clear.

Why does the Earth appear blue when viewed from space? The Earth's total surface area is approximately 510 million square kilometers, of which 71% is ocean, 2.5 times the land area. Although humans mainly live in the Northern Hemisphere, which accounts for two-thirds of the world's land area, it is worth noting that even in the Northern Hemisphere, the land area only accounts for 39.3% of the total area of ​​the hemisphere, while the ocean accounts for 60.7%. The same situation occurs in the Southern Hemisphere, Eastern Hemisphere, and Western Hemisphere, where the area of ​​the ocean always exceeds that of the land. These data clearly show that no matter where you look on the Earth, the ocean is the dominant geographical feature. It is precisely because of the vastness of the ocean and its properties of reflecting, refracting, and scattering sunlight that the Earth appears blue when viewed from space.

The colorful history of the Earth: From fiery red to azure blue

The Earth has not always been blue; it has gone through a variety of color changes over its 4.6 billion-year history.

South African photographer Sean Messham photographed the Nyiragongo volcano in Africa

When the Earth was first formed, its surface was almost completely covered by hot lava, which gave the Earth a dark red appearance, like a blazing fire. However, as time went on, the Earth slowly "cooled down" and the lava began to solidify, forming a vast black basalt crust, giving people a deep and slightly terrifying feeling.

About 600 million years ago, the Earth underwent significant changes. As water evaporated and cooled, coupled with frequent asteroid impacts, large amounts of water began to accumulate on the Earth's surface. Although the Earth was covered in water, this water was rich in iron. At that time, there was almost no oxygen in the Earth's atmosphere, so the iron could not react with oxygen. Instead, the iron interacted with elements such as hydroxide and sulfur to form an oxygen-free rust. It is this substance that dyes the ocean a unique green, adding a touch of exotic color to the Earth.

The Purple Earth Hypothesis

There is a controversial but widely circulated hypothesis that the Earth may have appeared purple at some point. The idea sounds mysterious and fascinating, as purple is often associated with romance and nobility. In that era, there was no chlorophyll on Earth, but a molecule called retinal played an important role in early microorganisms. This retinal is widely found in a type of microorganism called halobacterium, which has a strong ability to absorb light in the purple spectrum. Therefore, if a large number of such microorganisms existed on the surface of the Earth, they might have given the Earth a purple appearance. Although this theory has not been conclusively confirmed, it provides an interesting perspective on the early colors of the Earth, which is mind-blowing.

After the legend of the purple planet, the Earth entered a long and severe period. About 2.4 billion years ago, the Earth suffered an extremely severe ice age. This period was extremely long, the Earth was covered with heavy snow, and the temperature dropped sharply. For 300 million years, the Earth almost turned into an ice ball. Over time, the Earth gradually recovered from the ice age and began to show a blue color. The reason for this change is that most of the Earth's surface is covered by oceans, which absorb red, orange and yellow light, but reflect less purple light. Therefore, blue, green and cyan light, after being reflected and refracted by the sea water, work together to form the blue color we are familiar with today. This process marks the gradual transformation of the Earth from a cold white to a vibrant blue planet.

At present, the gray-blue color of the Earth we see is largely due to the damage caused by human activities to the environment. Before the large-scale production activities of humans, the Earth was a brighter blue, like a sparkling sapphire. Therefore, we must recognize the importance of protecting the environment. Let us work together to contribute to the future of the Earth and make it become that dazzling blue planet again.

The content is compiled from the official website of China's manned space program, etc.

(Scientific review: Guo Hongfeng, senior engineer of the National Astronomical Observatories of the Chinese Academy of Sciences)

This article comes from: China Digital Science and Technology Museum

Editor-in-charge: Wang Lei