Red and Blue Shift

The Doppler Effect

Sound waves travel out from the bike at the same speed in all directions

Sound waves still travel out from the bike at the same speed in all directions but the bike is moving and the waves are squeezed together in the direction of travel and less tightly packed in the opposite direction Sound waves which are closer together are higher in PITCH than those which are further apart.

The light is always redder than it should be from distant galaxies.

Red and Blue shift Red and blue shift does not measure the velocity of a galaxy or star relative to us but only a component of that velocity called the radial velocity Radial velocity Actual velocity

Red and Blue Shift   s Increasing wavelength

Red And Blue Shift   is positive for red shift  s Increasing wavelength  is positive for red shift  s is negative for blue shift  s  Increasing wavelength Use –Δλ in calculations So by inspection you can see whether the object is approaching or receding

Red and Blue Shift f An increase in wavelength is a decrease in frequency Use positive Δf for consistency  f = f s - f f fs Increasing wavelength Increasing frequency

Calculating Velocities

Calculating Radial Velocities

This object is approaching Calculation The wavelength of the hydrogen  line in the laboratory is 656.285 nm. The same line is observed to occur at 656.255 in the star Vega.. Is it approaching or receding? Calculate its radial velocity (taking c = 3 x 108m) This object is approaching

Calculation c = 3  108ms-1

Stellar Data Object Laboratory line value (nm) Measured value (nm)  Leonis H 656.255 656.293  Leonis Fe 435.256 435.275  Delphiius Na 615.315 615.301 Andromedae 656.778  Ursa Majoris 437.134 437.189

ECLIPSING BINARIES AND REDSHIFT

Light Intensity time

Velocity of recession +200 -200 time