Approaching Source Blueshifts the Line - Observational Astrophysics: Distance, Flux, Transits, and Spectra Step by Step

A negative radial speed gives a negative shift ratio. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

The radial speed source carries the sign

The same speed scale uses radial speed -1 meter per second.

v=-1\ \text{m}/\text{s},\quad c=6\ \text{m}/\text{s}

The shift ratio is negative

Dividing by the same light speed gives shift ratio -1/6, a blueshift training case.

\Delta\lambda/\lambda=-\tfrac{1}{6}