Changes

*The characteristic signature of [[hydrogen]] can be detected from various remote galaxies with its frequency shifted towards the red portion of the spectrum. This discovery was first made in the 1920s by V.M. Sipher by means of very primitive equipment and then confirmed by [[Edwin Hubble|E. Hubble]] in the late 1920s by far more sophisticated telescope after Slipher had turned his attention elsewhere.   

*The characteristic signature of [[hydrogen]] can be detected from various remote galaxies with its frequency shifted towards the red portion of the spectrum. This discovery was first made in the 1920s by V.M. Sipher by means of very primitive equipment and then confirmed by [[Edwin Hubble|E. Hubble]] in the late 1920s by far more sophisticated telescope after Slipher had turned his attention elsewhere.   

*Hubble realized that this galactic [[redshift]] can be interpreted as effect of something similar to familiar [[Doppler effect]] applicable to [[sound]] waves, i.e. a conjecture can be made that the distortions in the spectral signatures of the galaxies come from a reflection of their recessional velocity.   

*Hubble realized that this galactic [[redshift]] can be interpreted as effect of something similar to familiar [[Doppler effect]] applicable to [[sound]] waves, i.e. a conjecture can be made that the distortions in the spectral signatures of the galaxies come from a reflection of their recessional velocity.   

*The inference from the observations of spectra expressed in quantitative relationship (known as [[Hubble's law]]): the redshift of a galaxy thus its recessional velocity is:

*The inference from the observations of spectra expressed in quantitative relationship (known as [[Hubble's law]]): the redshift of a [[galaxy]] thus its recessional velocity is:

**proportional to its distance and

**proportional to its distance and

**inversely proportional to its apparent brightness or flux

**inversely proportional to its apparent brightness or flux