Photograph of Earth from space taken in 1972
In December 1972, the crew of the Apollo 17 spacecraft presented humanity with one of the most famous photographs of the Earth called “The Blue Marble”. The picture was taken from a distance of 29 thousand kilometers from the surface of the planet. At that moment, the Sun was behind the astronauts, thanks to which the Earth was well lit. The photograph is now in the public domain and is used in many works to depict the Earth from space. The picture is impressive, but for more than fifty years it has puzzled scientists – why is our planet so evenly lit? Indeed, due to the different reflectivity of the northern and southern hemispheres, one part of the Earth should glow brighter than the other. Recently, this phenomenon has finally been found an explanation.
Интересный факт: фотография «Блю марбл» была сделана спустя 5 часов 6 минут после запуска «Аполлона-17». Авторство приписывают не одному человеку, а всему экипажу миссии: Юджину Сернану, Роналду Эвансу и Харрисону Шмитту. Снимок был сделан на 70-миллиметровую камеру «Хассельблад» с объективом Zeiss.
The difference between the northern and southern hemispheres of the Earth
For many years, scientists have been convinced that the northern and southern hemispheres should look different. Seen from a relatively close distance below the clouds, indeed, the northern hemisphere is much better illuminated by sunlight than the southern. This is due to the fact that the hemispheres of our planet have different albedo is the reflectivity of the surface. The northern hemisphere looks brighter because it reflects light more due to the presence of more land. The southern hemisphere is covered by an ocean that absorbs light, making it appear darker.
Northern (left) and southern (right) hemispheres of the Earth. The image shows that there is much less land in the Southern Hemisphere
Недавно ученые объявили, что ядро Земли начало вращаться в другую сторону. О том, правда это или нет, мы рассказали в этом материале.
Why does the Earth glow in photographs?
But in a photograph of Earth from space in 1972, both hemispheres of the planet look equally bright. Scientists could not find an explanation for this phenomenon for more than fifty years. It was only recently that the secret was revealed – the answer was published in the scientific journal Proceedings of the National Academy of Sciences.
According to scientists, the surface of the Earth is covered with water by 70%
As part of a new study, researchers Ohr Hadas and Yochai Kaspi set out to find out if the brightness of the southern hemisphere as seen from space could be explained by thunderclouds. To do this, they studied the global weather database, which has been collected since 1950. It turned out that strong storms often occur in the southern hemisphere of our planet. They are accompanied by an abundance of clouds, which can reflect sunlight much better than the surface of the water. According to scientists, the land area in the northern hemisphere is twice as large as in the southern. But the abundance of clouds in the southern hemisphere compensates for this difference and the albedo indicators become almost equal.
We have found that the cloud albedo that occurs due to severe storms over the southern hemisphere is a highly accurate compensator for the large land area in the northern hemisphere, and thus the symmetry is preserved, said climatologist Or Hadas.
Secrets of the planet Earth
So, the uniform glow of the Earth in photographs from space now has an explanation. The northern hemisphere of our planet looks bright because it is covered with a large amount of land. The southern hemisphere does not lag behind in brightness because there are often strong curtains with a dense layer of clouds that reflect sunlight well.
Storms in the ocean greatly affect the appearance of the Earth from space
However, in the future, the difference in the brightness of the two hemispheres of the Earth may appear and become very noticeable. Computer models have shown that due to global warming, the frequency and strength of storms in the northern and southern hemispheres may change. However, scientists cannot say exactly what these changes will be. However, observations in this area could help researchers develop technologies to keep the Earth habitable for as long as possible.
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Apparently, in the future, scientists will have to learn a lot of new things about the Earth. One of the most important discoveries was made in 2023 – it was found out that an unknown structure is contained inside the core of our planet. My colleague Andrei Zhukov spoke in detail about this discovery in this article. I strongly recommend reading!
