🌍 Since ancient times, astronomers have sought to understand the position and movement of the Earth in the vastness of the Universe. In ancient times, the prevailing model was geocentrism. According to this model, the Earth was immobile at the center of the Universe. The planets orbiting the Earth followed complex trajectories, with the direction of travel changing on portions of the curve known as epicycles.
But some astronomers, like Eratosthenes, had already understood that the Earth revolved around the Sun. In the Middle Ages, despite strong repression from the Church, a new model took hold, placing the Sun at the center of the Universe: heliocentrism. This time, the planets of the solar system followed circular trajectories rather than complicated ones. Copernicus was the first to disseminate this model, which was simpler than the geocentric model with its epicycles. Then Galileo discovered four moons of Jupiter, irrefutable proof that not all stars orbit the Earth! Galileo thus defended what was then known as the Copernican model against the Church, and took the opportunity to flesh it out. For example, he discovered that the trajectories of the planets around the Sun were not perfect circles but ellipses, with non-constant speeds.
Little by little, discovery after discovery, the heliocentric model gave way to the current one. We now know that the Sun is not at the center of the Universe. Far from it: it's just one of billions of stars in our Milky Way galaxy, and our galaxy itself is just one of 2000 billion galaxies in the observable Universe... and the entire Universe extends far beyond our observable Universe!
We now know that the Earth's motion around the Sun does not describe a circle, but an ellipse. The distance separating us from the Sun is therefore not constant, and varies between 147 million and 152 million km. As for the speed at which the Earth moves, it's enough to make you dizzy.
Imagine you're sitting motionless on the surface of the Earth. It's moving in its orbit around the Sun at a speed of around 30 km/s. If it's moving around the Sun, the latter is also moving, dragging the planets in orbit, including the Earth, at around 220 km/s around the center of our galaxy. And since the middle of the 20th century, we can add to this the fact that our galaxy is plunging at over 610 km/s towards a mysterious region of the distant sky, the Great Attractor...




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💥The Mysteries of the Great Attractor:
- The Big Bang theory also predicts the emission of thermal radiation at the beginning of the Universe's history. However, in 1964, the cosmic microwave background was discovered by two American astronomers, Arno Penzias and Robert Wilson. This fossil radiation would have been emitted around 380,000 years after the Big Bang, when the Universe was smaller, denser and hotter. The Universe then expanded and cooled. The cosmic microwave background thus corresponds to the first instant when the Universe became sufficiently sparse for light to propagate. In fact, it's because light was able to illuminate the Universe and travel to our telescopes that we can trace it back to this instant.

While we still haven't completely solved the mystery of the origin of the world, for the moment, the theory of the Big Bang and the expansion of the Universe is the prevailing one. The space between galaxies is growing every day and, in theory, objects are moving away from each other at a speed of 2.2 million kilometers per hour at present. So does this mean that the galaxy next to ours is moving away at 2.2 million km/h? No, because unfortunately it's not that simple!


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🎬 Today's program:
- 00:00 - Introduction
- 13:05 - The attraction of the Great Attractor
- 23:12 - Discovering the Great Attractor
- 29:33 - The Great Attractor hidden by our galaxy
- 33:47 - Shapley's supercluster, an explanation for the mystery of the Great Attractor?
- 39:53 - 2017: solving the mystery of the Great Attractor
- 51:43 - So, what is the Great Attractor?
- 58:19 - The Great Attractor, a risk for our galaxy?


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