Light-time

Light-time is the product of the speed of light in a vacuum and time it takes light to travel a certain distance in space. It is most commonly used in light-years to calculate interstellar distances.

Common units of light-time

The light-second, light-minute, and light-year are the most common light-time units used.

Common units of light-time

Unit	Meters	Miles	Astronomical Units
1 Light-second	$2.9979\times 10^{8}{\mathsf {m}}$	$1.8628\times 10^{5}{\mathsf {mi}}$	0.0020 AU
1 Light-minute	$1.7987\times 10^{10}{\mathsf {m}}$	$1.1177\times 10^{7}{\mathsf {mi}}$	0.12 AU
1 Light-year	$9.4607\times 10^{15}{\mathsf {m}}$	$5.8786\times 10^{12}{\mathsf {mi}}$	63000 AU

For Mars, light time translates into communication times. For example, it could be said that at its closest Mars is xx minutes away from Earth, while at maximum separation it is xx minutes away.