The Hubble’s Law

In 1929, Hubble saw 18 galaxies, also estimating their distance. He also discovered that all the galaxies seem to move away from us. In fact, the radiation emitted by these galaxies moved towards the red, in the electromagnetic spectrum: this is called redshift. This phenomenon has a simple explanation: whenever a source moves away from us, the number of oscillation per second decreases, so the wavelength seems to raise and we are used to say that the light turns to red. While a source comes towards us, the number of oscillations per seconds increases, and so the wavelength decreases and the light seems moved to the blue (blueshift).
Hubble also showed that the movement was directly proportional to the speed of the bright source; he found a precise correlation between the distance of the galaxies and their recession speed, then called the Hubble’s Law, based on this formula:  v = H d where H is the Constant of Hubble, v is the galaxies departure speed and d their distance. The Universe, as matter of fact, is subject to an expansion movement and the Earth takes part to this inexorable motion, without being its centre.
In conclusion, it does not exist a privileged observer: the speed with the galaxies are moving away increases with the distance, from every place we can be. An other observer, placed in whatever point of a different galaxy, would exactly find the same law achieved by Hubble.

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