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One of the well-established properties of the Universe is that it expands
Clusters of galaxies move away from each other, which means that in the past they were closer, and there was a moment when this expansion began. This happened about 14 billion years ago, and we call it the moment of the birth of the universe. Today, you can see through a telescope only a region with a radius of no more than 14 billion light years, because from the more distant regions of the Universe, light has not yet reached us. But the size of this region is constantly growing, as the Universe is expanding and the boundary of the region accessible for observation is moving away from us at the speed of light. Therefore, over time, we will see more and more of the universe.
Since we do not know other forms of life besides our protein-carbon, we imagine the planets suitable for life to be similar to our Earth. We consider the temperature of the planet's surface as the most important condition for life: it must be such that liquid water can exist there. On the surface of the Earth, at normal atmospheric pressure, this is a temperature range from 0 degrees Celsius to 100 degrees Celsius. At temperatures below 0 degrees Celsius, water freezes, and at temperatures above 100 degrees Celsius boils.
But on other planets, where the atmospheric pressure is different, water behaves differently. Her freezing temperature is almost unchanged and is always close to 0 degrees Celsius, but the boiling point varies very much. At low atmospheric pressure, for example, on the surface of Mars, where the atmospheric pressure is almost 200 times lower than on Earth, water cannot remain liquid at all, but can either be in the form of steam or in the form of ice. While it is cold, it is ice, and as soon as the temperature rises above 0 degrees Celsius, the ice turns into steam, bypassing the liquid state. This process, when a solid immediately becomes a gas, is called sublimation, or sublimation. Therefore, on the planets with low atmospheric pressure, the "water" life forms familiar to us are impossible.
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How do you know that the universe is infinite?
The fact of the matter is that we do not yet know whether the Universe is infinite. And it is entirely possible that we will never be 100% sure of this. Indeed, to check whether the Universe is infinite, it would have to be measured, and for this, if the Universe is really infinite, it would take an infinitely long time. But we know for sure that the Universe is much larger than the part that astronomers can now see through telescopes.
The science that studies the Universe on a large scale is called cosmology, and the scientists who deal with this science are called cosmologists. In fact, these are astronomers and physicists who are interested in how our Universe was born, how it is structured as a whole and what fate awaits her in the future. Astronomers observe the Universe, study the distribution and movement of stars, galaxies and substances of an obscure nature in it, which is commonly called dark matter, and physicists try to explain what astronomers see in the framework of the existing theory, which constantly has to be developed and supplemented, as astronomers discover all new and unexpected properties of the universe.
The most grandiose collision of recent years, astronomers observed in July 1994, and it happened, fortunately, far from the Earth. Then, next to Jupiter, the nucleus of a rather large comet collapsed. Jupiter himself was to blame for this, and he destroyed the comet with his powerful attraction. For this he got: two dozen fragments, each a kilometer in size, bombarded a giant planet for several days. "Wounds" in the atmosphere of Jupiter were clearly visible from the Earth through a telescope. But after a couple of weeks they dragged on, and Jupiter "forgot" about this incident. If this happened on Earth, we would not so soon forget about it. However, our planet has preserved the memory of such attacks that occurred millions of years ago. About 200 large meteorite craters found on Earth. The largest of the studied has a diameter of about 300 km. Perhaps there is a larger one, with a diameter of about 500 km. They were formed from a collision of the Earth with asteroids 10-20 km in size. But it was a very long time ago, billions of years ago.
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