Editing Carl Wilhelm Wirtz (section)

== Scientific career ==

As already [[Vesto Slipher]] in 1912,<ref name="Kragh-2003" /> Wirtz in 1918 observed a systematic [[redshift]] of [[spiral nebula]]e, which was difficult to interpret in terms of a [[physical cosmology|cosmological model]] in which the [[Universe]] is filled more or less uniformly with [[star]]s and [[nebula|nebulae]]. Wirtz additionally used the equivalent in German of ''[[K correction]]''. The term continues to be used in present-day observational cosmology, but Wirtz's observational evidence that the [[Universe]] is expanding is not often mentioned.<ref name="Kinney-1996" /> He wrote:<ref name="Wirtz-1918" />

{{Quote|1=It is remarkable, that our system of fixed stars shall have such a very strong displacement of 820 km/s, and equally strange is the interpretation of the systematic constant k = + 656 km. If we ascribe a verbatim interpretation to this value, then this means that the system of spiral nebulae is drifting apart by a velocity of 656 km with respect to the momentary location of the solar system as the center.}}

In 1922,<ref name="van den Bergh-2011" /> he wrote a paper where he argued that the observational results suggest, that the redshifts of distant galaxies are becoming higher than more closer ones, which he interpreted as an increase of their radial velocities with distance, and that larger masses have smaller redshifts than smaller ones.<ref name="Wirtz-1922" /> In another note of the same year, he argued that counter-clockwise spiraling galaxies have smaller redshifts than clockwise spiraling ones.<ref name="Wirtz-1922b" /> In 1924 he obtained more precise results, and interpreted them both as a confirmation of an increase of radial velocities with distance, but also as confirmation of a [[de Sitter universe]], in which the increase of redshift is seen as caused by an increased [[time dilation]] in distant parts of the universe.<ref name="Wirtz-1924" />

In 1936, Wirtz wrote a short paper alluding to the priority for his 1922-conclusion that the radial velocities of galaxies are increasing with their distance.<ref name="Wirtz-1936" />