We use:
$$ 5\times10^5 $$
Everyone should be familiar with this.
$$ 1\text{AU = the distance from the Earth to the Sun} $$
This is only used inside our solar system.
93 million miles
How far light travels in a year. This is not a unit of time.
$$ 1\text{LY}\approx\text{6 trillion miles} $$
Used to measure to objects outside of solar system.
Paralax of one arcsecond
denoted as the letter c
$$ c=3\times10^8\text{ m/s} $$