a hypothesis known as the 'tired light' theory suggested that light loses energy during its long cosmic journeys, leading to the redshift. However, as it failed to explain numerous observations ...
Drawing upon data from Vesto Slipher and Henrietta Leavitt, Hubble demonstrated a correlation between galactic distance and redshift. ... We now know this is due to cosmic expansion. Space itself ...
As the light was shifted towards the red end of the spectrum (lower frequency/longer wavelength) this phenomenon was termed 'redshift'. Figure caption, Lower diagram shows spectrum of light ...