Work out redshift instantly with clear inputs, formula shown and shareable results.
Redshift is the fractional wavelength shift, z = (lambda(obs) - lambda(rest))/lambda(rest). The H-alpha line at 656.3 nm observed at 700 nm gives z = 0.0666, implying a recession of about 19,300 km/s from the relativistic Doppler relation. Negative values are blueshifts, as seen from the approaching Andromeda galaxy.
Redshift
z = (lambda(observed) - lambda(rest)) / lambda(rest)
Relativistic Doppler
beta = ((1+z)^2 - 1) / ((1+z)^2 + 1)
Not strictly. For distant galaxies it comes from the expansion of space stretching the wave in transit, though at small z the two give the same answer.
Because the simple v = cz overestimates velocity once z passes about 0.1, and becomes badly wrong beyond z = 1 where it would imply superluminal motion.