Somebody explain it to me...
red·shift
/ˈredˈSHift/
noun
ASTRONOMY
noun:
red shift
- the displacement of spectral lines toward longer wavelengths (the red end of the spectrum) in radiation from distant galaxies and celestial objects. This is interpreted as a Doppler shift that is proportional to the velocity of recession and thus to distance.
https://en.wikipedia.org/wiki/Redshift
In
physics,
redshift is a phenomenon where
electromagnetic radiation (such as light) from an object undergoes an increase in
wavelength. Whether or not the radiation is visible, "redshift" means an increase in wavelength, equivalent to a decrease in wave
frequency and
photon energy, in accordance with, respectively, the
wave and
quantum theories of light.
Neither the emitted nor perceived light is necessarily red; instead, the term refers to the human perception of longer wavelengths as
red, which is at the section of the
visible spectrum with the longest wavelengths. Examples of redshifting are a
gamma ray perceived as an
X-ray, or initially visible light perceived as
radio waves. The opposite of a redshift is a
blueshift, where wavelengths shorten and energy increases. However, redshift is a more common term and sometimes blueshift is referred to as negative redshift.
There are three main causes of red (and blue shifts) in astronomy and cosmology:
- Objects move apart (or closer together) in space. This is an example of the Doppler effect.
- Space itself expands, causing objects to become separated without changing their positions in space. This is known as cosmological redshift. All sufficiently distant light sources (generally more than a few million light years away) show redshift corresponding to the rate of increase in their distance from Earth, known as Hubble's Law.
- Gravitational redshift is a relativistic effect observed due to strong gravitational fields, which distort spacetime and exert a force on light and other particles.