Why doesn't the sky fall down on our heads?. Aydogan Koc

interesting examples and clarifying short stories or maybe new questions. I hope you will contribute to the next edition with your questions.

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      Introduction – Why doesn’t the sky fall down on our heads?

      You know, almost all children (or those who are still children in their hearts) know Asterix the Gaul, his fat friend Obelix and the fierce and fearless village chief Vitalstatistix very well. He is known to fear neither the Romans nor the Vikings or other dangers in nature. He only has two problems: One of them is his wife, Impedimenta, and the other is the possibility of the sky falling on his head one day. As it is a known fact that men have no chance against women, we can consider the first problem as unsolvable and we can forget about it. But his second fear still exists, he is still anxious about the sky falling down on his head.

      When we look at the open sky at night, everything is in order and beautiful harmony exists. All celestial bodies and planets move in the firmament the way they should, the Sun rises in the east and sets in the west, day after day!

      That is why humans in the early days believed that the Earth is at the center of the universe. Only in recent centuries did people understand that the planet we live on is one of the eight known planets in our Solar system. These planets keep moving in their elliptical orbits at great distances around the giant Sun.

      How insignificant and small our planet is can easily be demonstrated by a scaled model of the universe. Assuming 10 cm represents 1 million km; our Sun would be an orange 14 cm in diameter, looking like a yellowish lantern. Our world is the size of a grain of sand with a diameter of 1.3 mm circling the Sun at a distance of 15 m. The closest star to our Sun is the dwarf Proxima Centauri which is about the size of a cherry and is 4,000 km distance in our scale model. This equals the distance between Ağrı/Turkey and Madrid/Spain.

      In our universe, every celestial body is on the move. Our world rotates around its own axis once a day, which is a speed of 1,670 km/h at the equator. Our satellite, the Moon, orbits the Earth in 29.5 days. This is an average orbital speed of 3,700 km/h. The average speed of our Earth orbiting around the Sun for a full circle in 365.25 days is 107,000 km/h. Our life source, the Sun, travels at about 1 million km/h around the center of our galaxy called The Milky Way.

      There is only one single force which prevents planets, moons, stars and galaxies from drifting apart: this force is called gravity. It can only be balanced by the centrifugal force which is the result of orbital motion. Consequentially, there is a ballet of celestial bodies in the universe which move around each other in perfect harmony, maintaining their existence thanks to the balance of these forces and, unless this balance is impaired, all these celestial bodies will continue their movements for the next millions or even billions of years. Therefore, chief Vitalstatistix really need not worry about the sky falling down on his head one day.

      Maybe we should worry a little. When we consider all the small and large celestial bodies in our solar system, we see that this question is something worth worrying about.

      There are millions of large and small meteorites, asteroids and comets other than the known planets and their satellites in our own Solar system. Their orbits easily change when they collide with other bodies or due to gravity when they get too close to other planets and stars. As a result, there is a small risk of colliding with the Earth. It is known that many celestial bodies have fallen onto the Earth as a result of these encounters.

      For example, it has been proven that a meteorite hit the Mexican gulf about 65 million years ago. It is estimated that this event turned living conditions on Earth upside down and probably caused the extinction of dinosaurs. The magnitude of the damage to be caused by collision of a celestial body with the Earth depends on the size of the celestial body. The main criterion is whether the average diameter exceeds about 30 m, since these celestial bodies need to pass through the gas layer around us called the atmosphere at a very high speed to reach the surface of the Earth. During this transition, many celestial objects burn to ashes or hit the ground in tiny pieces due to increased frictional heat. The large objects can indeed pose a risk to life on Earth. That is why the focus is on rather large celestial objects. Asteroids and meteorites, with an average diameter of a few kilometers, are closely monitored as soon as they are identified. Luckily, there is no immediate risk to the Earth. The probability that a meteorite with an average diameter of 1 km will hit the Earth is estimated to be once in about 300,000 years. However, not all of the small asteroids are being monitored yet, and the probability to collide with one of them is slightly higher. Therefore, it is theoretically possible that this kind of celestial body can cause a small disaster after hitting an inhabited area on the Earth.

      Vitalstatistix, thus, needs to think about taking appropriate safety measures in advance. Scientists already have some ideas.

      We don't really need to live in continuous anxiety. The probability of other natural disasters seems to be higher than the collision with an asteroid. As you know, when Vitalstatistix encounters a problem, he always summons two of his best men: the fat Obelix and his cunning friend Asterix. This reassuring attitude is also being taken by the international space community; the first French artificial satellite to be launched with a Diamant-A rocket on 26 November, 1965 was called Asterix.

      1. The History of Aviation

       When was the first flight in human history?

      Let's go back to one of the most popular stories of the Ancient days, the story of the inventor and craftsman Daedalus. A slave on the Crete Island, Daedalus constructed a building for King Midas called the Labyrinth. Looking for ways to escape with his son, Icarus, Daedalus came up with a new idea. He would build large wings for Icarus and himself by combining the feathers of an eagle with wax and then they would fly to freedom.

      Daedalus was anxious about the flight as he knew the Sun would melt the wax. Thus, he warned his son not to get too close to the Sun. Overwhelmed by the giddiness of flying; Icarus soured into the sky and then came to close to the Sun which melted the wax. His father's warning became sad truth; Icarus plunged into the sea and was killed. Thus, aviation had its first fatality.

      Since then, human beings watched birds and flying creatures with great fascination and slight envy and tried to imitate them. Humans studied, tried, failed but did not give up.

      The person who probably designed the first flying machine in the 15th century was a scientist and artist, Leonardo da Vinci. A century later, Francesco di Terzi started to sketch the first lighter than air ships. But humanity had to wait for more than another century for construction of an actual flying machine.

      The first man-made flying machine flew on 21 November, 1783. The hot air balloon constructed by the Montgolfier brothers rose into the French sky. A few days later on 1 December, 1783, a French Physics Professor, Alexandre Charles, managed to fly with a hydrogen filled balloon.

       When was the first airlift used for ´human transport built?

      Paris, the capital of France, was besieged by the Germans in 1870. Paris lost all contact with the rest of France. The people of Paris, looking for a way to send messages to other cities, decided to use manned balloons. For the first time, on 23 September, 1870, Jules Darouf managed to fly over the German lines with his balloon. Jules crossed the occupation lines and landed on independent French territory three hours later.

      The second aviator