Final answer:
Hubble's Law states that the farther away a galaxy is, the faster it's receding from us, which can be described by the equation V=Hxd. This correlation has been observed by measuring redshift in the light from galaxies, implying that the universe is expanding.
Step-by-step explanation:
The relationship between the distance of a galaxy from Earth and its velocity is described by the Hubble's Law, which indicates that the farther away a galaxy is, the faster it is moving away from us. This observation is essential for understanding the expansion of the universe. The law can be expressed with the simple equation V = H × d, where V is the recessional velocity of the galaxy, H is the Hubble constant, and d is the distance of the galaxy from Earth.
Galaxies' recessional velocities can be measured by analyzing the Doppler shift in the light they emit, which stretches its wavelengths and shifts it towards the red end of the spectrum, known as redshift. Moreover, it is not the movement of galaxies themselves causing this recession but rather the expansion of space. The more distant galaxies seem to recede faster, a phenomenon consistent with the explosive expansion of the universe from an initial state, often related to the concept of the Big Bang.
Local motions, such as gravitational interactions with nearby galaxies, can cause deviations from the expected velocity given by Hubble's Law. However, for nearly all galaxies beyond our own local group, the principle that the greater the distance, the greater the speed of recession holds true.