Red Shift, Blue Shift Radial velocity – the movement of an object toward or away from us An Observer Velocity away Velocity toward

Red Shift, Blue Shift Blue shift – an object moving toward an observer Red shift – an object moving away from an observer An Observer Wavelength is shortened – blue shift Wavelength is expanded – red shift

Astronomical Shifting Star moving toward us – all spectral lines are shifted blue-ward (shorter wavelengths) Unshifted Spectrum Blue Shifted Spectrum

Astronomical Shifting Star moving away from us – all spectral lines are shifted red-ward (longer wavelengths) Unshifted Spectrum Red Shifted Spectrum

Radial Velocity Two Identical Stars

Radial Velocity No shift is seen (radial velocity = 0)

Radial Velocity 1: Moving away from us 2: Moving toward us

Radial Velocity 1: Maximum velocity away from us 2: Maximum velocity toward us

Radial Velocity 1: Still moving away from us 2: Still moving toward us

Radial Velocity No shift is seen (radial velocity = 0)