FAQ astronomy

All galaxies are receding from us. One might think that the Milky Way is the center of the Universe, unfortunately, has arranged the universe so that the inhabitants of each galaxy are exactly the same as us. They observe all the galaxies away and they all have the illusion that they are at the center of the universe. The universe is everywhere the same. The center of the world is everywhere at the beginning of the universe we were all at the center.
How did the universe he could play this hocus-pocus? Simply by using the fact that the escape velocity of a galaxy is proportional to its distance. On a motorway, at nightfall, a line of cars leaving Paris. The speed of each car traveling is all the greater because it is farther from Paris. Julie is just 1 km from Paris. His car was traveling at 10 km/h. Pierre is 2 times farther than 2 km from Paris and led to 20 km/h. Isabelle 3 km and traveling at 30 km/h. Remi 4 km and traveling at 40 km/h. Peter notes that Julie's car which is 1 km away from behind his own 10 km/h. Isabelle 1 Km before him away as 10 km/h, while Remi 2 km before it departs at 20 km/h. Isabelle finds exactly the same movements as Pierre, she saw Peter and Remi at 1 km distance away at 10 km/h, while Julie 2 km widening its gap to 20 km/h. Each driver sees the other 's away from it at a speed which increases from 10 km/h for each km away. Example from the book by Trinh Xuan Thuan "The secret melody".

The planets move in their orbits. This balance is maintained by centrifugal force that compensates the gravitational force Sun. The nearest planets are more strongly attracted than the more distant. Consequently, the velocities decrease with distance (40 km/s Mercury for up to 4 km/s for pluton). Pluto 100 times farther than Mercury moves 10 times slower. All these velocities we can calculate the Sun's mass is 2x10 ³⁰ kg or 333 000 times the mass of the Earth which is easier to remember.

The Hubble observations we suggest a simple calculation. We measure speed and distance of galaxies. How long they have taken to reach this distance away at this speed? The answer we give an approximate age of the universe. Some stars our Galaxy shine for more than 13 billion years.

In a flat space, the sum of 3 angles of a triangle is 180 °. In a spherical space is greater than 180 ° in a hyperbolic space, it is lower.
There has never been able to show any curvature of cosmic space. Its radius is greater than several billion light years. The curvature of space is closely related to the density of matter (Einstein). A critical density universe would have a planar geometry. If the density exceeds the critical density, space is curved like a spherical surface, if lower, it is curved like a hyperbolic surface.
The curvature of the sphere is that of a closed universe of finite volume, which eventually shrink.
The hyperbolic curve corresponds to that of an open universe of infinite volume and indefinite.

The universe observed by our telescopes shows a radius of 15 billion light years. It contains 100 billion galaxies and 10 ⁸⁰ nucleons. The more we retreat into the past, over this mass of matter is concentrated in a small space. This theory says that initially it was contained in a tiny volume. Only our observable universe is only a small part of the real world.

This measure is based on the Doppler effect. Compared to its real color, the light of a star approaching seems bluer, if removed, it is redder. The observation was made by Edwin Hubble in 1930. The galaxies recede even faster than they are more distant.
galaxy located 10 million light years away at 200 km/s, while a galaxy located 100 million away from AL to 2000 km/s.
A trio of galaxies form a triangle whose area increases without changing their angles.
The galaxies are driven by the stretching of space. This gave birth to the Big Bang theory.

Stars and galaxies are made of 98% hydrogen and helium with always the same proportion, 3 / 4 hydrogen and 1 / 4 helium. In nature, there are no stable nuclei consisting of 5 or 8 nucleons. These structures disintegrate almost spontaneously. These gaps in the sequence of kernels stable partly explain why the Big Bang has not produced more heavy nuclei.
The chain of successive catches of nucleons it is interrupted.

We have long known that our planet orbits the Sun and that it orbits the Milky Way. This movement combined with that of our Galaxy in the Virgo Cluster and that this cluster in the Universe, composed a global movement. However there is no absolute motion. It moves relative to a benchmark assumed motionless. The reference here is the set of particles CMB.
The measured speed is 620 km/s.
The local group is part of a huge complex of 10 000 galaxies assembled in clusters spanning some 200 million light years, called Supercluster or Local Supercluster the NEWS Madonna. The Supercluster and the Virgo Supercluster to the Hydra and Centaur fall themselves to another large city clusters of galaxies known as the Great Attractor.
From our land base, we participate in a fantastic ballet Cosmic Earth propels us to 30 km/s around the Sun, which splits the space at 230 km/s around the Milky Way. This falls turn toward the Andromeda Galaxy at 90 km/s, each of the galaxies are rushing to 45 km/s toward the center of the Local Group our galaxy clusters.
Local Group moves at 600 km / s attracted by the cluster of galaxies of the Virgo supercluster and the Hydra and Centaurus, which in turn falls to the great attractor.

The material, nebulae, stars, planets, molecules, atoms are made up of protons, neutrons and electrons. Protons and neutrons (nucleons) are composed of quarks. Quarks come in 6 flavors u, d, s, c, t, b. The proton is made of 2 u quarks and 1 d quark The neutron consists 2 quarks and 1 d quark u. Each quark has an additional property named "color"; There are 3 "blue", "green" and "red".
The atomic nuclei are clusters of protons and neutrons. The atoms are formed a nucleus around which electrons orbit. Each atom corresponds a chemical element. There are a hundred. Each carries a number that specifies the number of protons in its nucleus and the number of electrons orbiting its train. The No. 1 is hydrogen, helium 2, 6 is carbon, the 26 is iron, lead 82...

These are massless particles that travel at the speed of light that are emitted in abundance by stars.
They interact very weakly with matter. Hundreds of billions of neutrinos pass through our bodies every second.
The electrons and neutrinos belong to the family of leptons, while the quarks and baryons are nucleons or hadrons.

The electron is rather a kind of point electric weighing, and no one knows or where he is or where it goes. It turns on itself like a top uncontrollably and he has some form of collusion very discreet (weak interaction) with most other particles. It belongs to the family of leptons, where he occupies the place of honor. In the quantum world, this means that when a force acts on it, she meets an object without extension, at a specific point, not a ball that would have a certain volume.
If you want to predict where to find it, even with the most precise calculations, you will get vague information like "this electron is somewhere there in an area of some 10-10 meters and it goes to almost up to tens of thousands of kilometers per second. And if you want to be more specific about its position, you may need to be even more unclear about its direction and its speed and vice versa.
* see article

The nuclear force. It changes the color of quarks, glue quarks into nucleons and nucleons in nuclei. It is a force short range (10 ^-13 cm).
- The electromagnetic force binds the atoms in molecules. Its influence diminishes with the square of the distance.
- The weak force changes the electron neutrinos and vice versa. It also changes the flavors of quarks, transforming a quark d u quark in a neutron decay into a proton. It is a force of short range (10 ^-16 cm).
- The force of gravity is the relationship of galaxies and stars. It acts on all matter universally. It is a force of infinite range.
All these forces are the agents of cohesion of nature.

250 BC Eratosthenes measured the shadow of the columns in Syene and Alexandria, June 21 at noon and knowing the distance from Syene to Alexandria, he deduced the circumference of the Earth. He found 40,000 kms, excellent value for the time.

In 1543 the Polish canon Nicolas Copernicus presented this principle into question the 2000 year old who said that the Earth was motionless and heavens revolved around it. The land was relegated to other planets to do an annual revolution around the sun. Copernicus granted the motion on Earth and stars immobility.

How an electron can be both wave and particle? Nature is so made, the dual nature of particles has been verified repeatedly in laboratory. Our sense is not a good guide when it comes to the world of the infinitely small. The particles have two aspects. They represent two valid descriptions of nature and complement one another. In a nuclear landscape, the principle of complementarity of the physicist Neils Bohr adds to the uncertainty principle of Heisenberg.

After all, macroscopic objects are made of microscopic particles, but the probability of a hazardous event occurs, ask to have eternity ahead. The answer is in the number of particles, the chance to neutralize and is very small in favor of determinism. Nevertheless it is never completely absent, the quantum uncertainty would allow the moon to leave its orbit if we had of eternity.

Time is elastic and malleable. Space, too. Both can expand, shrink, stretch, shrink at will. Both players cosmic drama are very united couple whose movements are always complementary. When the time is stretched when it passes more slowly, space shrinks. There is no absolute time, 87% of the speed of light, time passes land twice as fast but space contracts, 99% the speed of light, time passes 7 times slower and 99.9%, 22.4 times less quickly.
In Einstein's universe, space and time are inextricably linked. The concerted deformations of space and time can be considered transmutation of space-time. The space narrowing becomes time stretching and going slower. We obtained a second time to 300,000 kilometers of space. Since Einstein, the universe has four dimensions. The dimension time addition to the three dimensions of space.

If there are seasons on Earth, thanks to the inclination of the axis of rotation Earth relative to the ecliptic. This axis is tilted by 23 ° 27 '. Nevertheless, it is not static, it is recovering from 1 minute every 125 years or 1 degree every 7500 years.
In 177 000 years the Earth will be perpendicular to the ecliptic and in this position, there will be no seasons on Earth as we know it.

Aristotle believed that heavy objects fell faster than lighter objects. By ingenious reasoning, Galileo (1564-1642) showed that This could be the case. Suppose that fires two objects, one heavy and a light from the top of a tower. These two items are not free, but attached by a string. The question is: does the light object attached subject to heavy delays or hastens the fall of the latter to ground?
If Aristotle was right, the light object, falling less quickly than the object heavy on the string would delay and the fall of heavy object. But we can equally well argue that the two objects attached together form a system heavier than the only heavy object, and therefore the two items together must fall faster than the only heavy object. So if Aristotle was right, we would to the absurd conclusion that the presence of the object throws light and delays along the fall of heavy object!
The only way to avoid this absurdity is to conclude that the presence the light object in no way affect the fall of heavy object that is to say that the object light falls to the ground as soon as the subject heavy. The experiment was conducted on the surface devoid of atmosphere of the Moon by U.S. astronaut using a golf ball and an iron hammer.

We observe an oscillation of the Sun every 12 years. This corresponds to the cycle Jupiter's gravitational disrupts the Sun by its rotation around him. The search for exoplanets is therefore to identify the oscillations of stars in features identical to the Sun. This hunt is limited for now as gas giants which revolve around their star. More and more new stars are discovered with cyclical fluctuations.
Another characteristic of the presence of planets is the variation of brightness of a star. Telescopes to measure brightness, whose accuracy is 1% variation can also confirm the presence of planets around a star. Each time the planet to the star to be a darkening, a repeated cycle confirms a transition object to the star. 70 planets have been detected as well.

Antimatter is made up of antiparticles. An antiparticle has exactly the same mass as the particle corresponding quantum numbers but opposite. For example, the anti-electron has a positive electrical charge and the same magnitude as that of the electron. By combining antiprotons, antineutrons and anti-electrons, it is possible to make anti-atoms. Atoms anti-hydrogen have already been produced.
When a matter particle meets its antiparticle, they annihilate each other releasing all their energy as radiation. The anti-collision particle-particle are commonly used in experimental particle physics.
The life of antimatter in our environment is very low since early meeting of matter and annihilates then. There is no antimatter on Earth or in the solar system or even in our galaxy. It even seems that there Nowhere in the universe of antimatter in significant quantities, which may for example form of antimatter stars. However, the Matter and antimatter are believed to have been created in equal quantities during the Big Bang. The fact that any antimatter has disappeared is an unexplained phenomenon for now.
The first antiparticle, the anti-electron, was discovered in 1933 using cosmic rays. Indeed, the cosmic ray particles interact with the atmosphere and can then create antiparticles.

An atom contains a nucleus located at its center and electrons "rotate" around the nucleus. The nucleus contains nucleons, i.e. protons and neutrons.
Electrons have a negative electrical charge. Protons have a positive electrical charge, the same value as that of the electron. Neutrons have no electrical charge, they are neutrals.
It is exactly the same number of electrons and protons in a atom, an atom is electrically neutral. The number electrons (or protons) in an atom determines its properties physical and chemical, is the atomic number. For example, a hydrogen atom has 1 electron and 1 proton, the atomic number of a carbon atom is 6, that of an oxygen atom 8, an atom iron 26, a uranium atom 92, etc. (see table of elements)...
The number of neutrons in an atom varies, in general it is close to the number of protons. Two atoms of the same atomic number but with a different number of neutrons are isotopes: their chemical properties are identical but their properties are physically different (eg, certain isotopes of atoms stable are radio-active). To differentiate between the isotopes them, it usually gives the number of nucleons with the name the atom. For example, uranium-235 contains 92 protons and 143 neutrons (235 = 92 143) and uranium-238 contains 92 protons and 146 neutrons (238 = 92 146).

To fully realize what an atom we will grow a thousand billion times a hydrogen atom. To moment:
- The kernel consists of a single proton, it has a size of a mm and a mass of 1.7 million tons!
- The single electron is smaller than one micron (one thousandth millimeter) and a mass of 900 tons!
- This electron "runs" around the nucleus in a volume of about 100m in diameter: the size of the hydrogen atom, while the remains empty.

A man's height, that is 1.70 meters, the view goes up to 4 560 meters
At a height of 6 meters, the view goes up to 8 000 meters
At a height of 10 meters, the view goes up to 10 000 meters
At a height of 15 meters, the view goes up to 12 875 meters
At a height of 30 meters, the view goes up to 17 702 meters

A galaxy is a congregation of stars, interstellar matter and possibly large amounts of dark matter, whose cohesion is ensured by gravitational forces.
mass of a galaxy is an order of magnitude greater than one hundred million solar masses. The Galaxies interact with their neighbors and these interactions affect their form. Two galaxies can sometimes merge.
Galaxies are of three types: elliptical, spiral, irregular. As the stars that are grouped into galaxies, most galaxies are gravitationally bound together. The structure containing up to fifty galaxies known group of galaxies.
structure containing thousands of galaxies grouped in a few megaparsecs sector is a cluster of galaxies. Groups and clusters of galaxies are themselves grouped into superclusters, giant collections containing tens of thousands of galaxies.
In very large scale distribution of galaxy clusters is not uniform, but organized into plates or filaments.