# What does cz mean?

Take DS Geminorum for example, it has a cz of -2.33 [2.96]

My question is what does cz mean, what does is represent? and what does the value in the brackets mean?

http://simbad.u-strasbg.fr/simbad/sim-id?Ident=ds%20gem

## 1 Answer

It stands for the speed of light ($$c$$) times the redshift ($$z$$) as measured from the redshift of the spectrum. It is equal to the line-of-sight velocity that the star has. Positive means going away from us. It is given in a heliocentric reference frame, that is corrected for the rotation of the Earth around its axis/the Sun.

The -2.33 is the velocity (km/s) and the [2.96] is its uncertainty.

• $cz$ is the line of sight velocity, if $z \ll 1$. – Rob Jeffries Jun 23 '19 at 15:47
• Normally it holds for individual stars. See comment above for cosmological scale. – Alchimista Jun 24 '19 at 9:27