How come people say 5,000 km and not 5 Mm?
why not just say millions of meters or Mega meters?
On Earth it’s just not needed. In nearby space it could make sense — distance to the Moon is 369 Mm. Distance to the Sun 149 Gm. But people aren’t good at visualizing the difference between kilo-, mega-, and giga-. It isn’t obvious from those numbers just how much further away the Sun is.
For interplanetary space and beyond the time it takes for light to cross the distance makes more sense, I’d say. The moon is about half a second away, the sun about eight minutes, Voyager I a bit less than twenty hours, Alpha Centauri or Barnard’s about four years, and so on…
Would it surprise you to know that there is a unit of length that is specifically the distance between the earth and the sun?
It’s called Astronomical Unit.
