How come people say 5,000 km and not 5 Mm?
why not just say millions of meters or Mega meters?
Familiarity I guess. Mega isn’t really a widely used prefix outside of computers. We even say tons instead of megagrams.
But only in regards of nuclear bombs. Maybe it’s because of the scientific origins of these fields. Probably the same reasons why Americans measure firearm munition in mm.
Firearm’s ammunition is a mixed bag because many military sizes are standardized with the rest of NATO. 5.56, 7.62, and 9 mm sure; but then you get a bunch measured in caliber .308, .45, .50.
megaton, megawatt, megapascal, megacandela (for military flares), megahertz, megajoule, megaohm, megabequerel
To be fair, mass is weird because the base unit is kg (yes, the name includes a prefactor). I have no idea how they managed to fuck it up that badly.
Yes, I think it’s a question of use. I can’t think of many examples where you would quickly need to know the measurement to the nearest Mm. Maybe if for some reason you deal with a lot of lunar orbits? Diameters of exoplanets?
Any earth distances we need to know with greater precision, and any stellar distances are probably better measured in light years, etc.
Megameters sounds scary and I don’t want to alarm the people I’m talking to.
I do. Unfortunately, I don’t have many opportunities to do so. Which may be the reason why people don’t say megameter.
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.
That unit is used a lot in the space game Elite Dangerous. Never saw it used before that, but it made sense because it’s the next jump up in large units, and it also helps keep the UI clean looking.
