When we observe distant stars and galaxies, it is not because they are physically moving away from us at the speed of light. Rather, their apparent motion away from us is a result of the expansion of the universe. This phenomenon is known as the cosmological redshift.
The cosmological redshift occurs because the space between galaxies is expanding. As a result, the wavelengths of light traveling through this expanding space get stretched, causing them to become "redder." This shift towards longer wavelengths is commonly referred to as redshift.
The amount of redshift in the light from distant objects is directly related to their relative velocity with respect to us and the expansion of space between us. However, it is important to note that the expansion of space does not cause objects to move away from us faster than the speed of light. The redshift is a result of the stretching of the light waves as they traverse expanding space, not due to the objects themselves physically moving away faster than light.
Despite the cosmological redshift, we can still observe distant stars and galaxies because the light they emit, even though redshifted, continues to reach us. The light emitted by these objects travels through space at the speed of light, and while its wavelength is stretched, it is still detectable by telescopes on Earth or in space.
Scientists use various techniques to measure the amount of redshift and interpret it to determine the distance and velocity of objects in the universe. By studying the light from distant stars and galaxies, astronomers can gain insights into the history, composition, and evolution of the universe.