The Lorentz factor, due to relativity, also known as the Time Dilation Factor, is deﬁned thus:

$\gamma =\frac{1}{\sqrt{1-\frac{{v}^{2}}{{c}^{2}}}}$

Where,

v Is the object’s velocity

c Is the speed of light

$\frac{{v}^{2}}{{c}^{2}}={\left(\frac{v}{c}\right)}^{2}$

$\frac{v}{c}=0.9\to $

$\gamma =\frac{1}{0.43588989...}$

Dirk