Receding Source Redshifts the Line - Observational Astrophysics: Distance, Flux, Transits, and Spectra Step by Step

A source moving away stretches its spectral lines to longer wavelengths, a redshift, because each wave crest is emitted from farther away than the last. At low speed the shift ratio tracks the radial velocity directly, Delta lambda / lambda = v / c. The exact value holds only for a clean line, a known rest wavelength, and the low-speed model; real spectra add calibration error, line blending, relativistic corrections, and instrument resolution limits.

A positive signed speed gives a positive normalized line shift. 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 shift ratio is radial speed over light speed

The training light speed is 6 meters per second and the radial speed is 1 meter per second.

\frac{v}{c}=\frac{1\ \text{m}/\text{s}}{6\ \text{m}/\text{s}}

A positive signed ratio is a redshift training case

The checked shift ratio is 1/6. The lesson does not claim a real line profile.

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