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Never heard anyone use megameters either. They either stay on kilometer, or switch to miles. And miles mean different things from one place to the next.
Who switches to miles if they initially use km? They're the same order of magnitude.
Scandinavians do, 1 scandinavian mile = 10 km.
Only in Sweden and Norway.
Denmark used a different mile and it was just as magnificent as our infamous superior number system.
One Danish mile was 12000 alen, where one alen was 2 feet. However the foot was slightly shorter than the English foot.
In total the Danish mile was 7532.48 metres.
Most places aren't that far away in Denmark, so another common measurement was the fjerdingvej, which was a quarter mile.
Famous scientist Ole Römer made the suggestion to the king to measure all main roads in the period 1691-1698 using this standard. If you walk on old roads, you might find the old milestones placed at the quarter miles. To differentiate the quarter miles from actual miles, they'd have 1-3 holes on the surface.
The whole thing was redone numerous times since then using different scales, where some stones were moved around so it's completely useless today, but it always makes me happy when I find one.
Megameters are somewhat common in astronomy, for example when describing low orbital hights.
Really? I would have though that they would use the scientific notation in meters, so that the numbers are explicitly clear.
Never seen that for a distance, interesting thought.
Huh? Why would you switch to miles from kilometers?
And IMHO megameters aren't used that often because there is rarely anything useful to measure with it. Using a different unit makes you lose your sense of scale (e.g. the earth has a radius of ~7000km, not 7Mm) and for astronomy megameters aren't big enough most of the time (and you might as well use lightseconds/years because gigameters give no real intuition of scale).
Megameter is a real thing though, it's 1,000 km or 1,000,000 meters
Never heard anyone use megameters either.
I've used it in one specific situation - Physics classes in my freshman Chemistry uni year. The same professor would also use megagrams for weight.
It was mostly so the students got a bit more comfortable converting units back and forth, specially past the 10³~10⁻³ range.
Weird, I've never used anything other than unit*10^n on physics. it's just simpler to operate. 1e3m is 1km, 1e6g a megagram. When working on science, I much prefer the scientific notation.
It looks a bit less cluttered, compare e.g. "40.0 Mm" "40.0 x 10⁶ m" or "4.00 x 10⁷ m". Plus I think that he took into account that he wasn't lecturing future physicists but future chemists - in Chemistry you rely on those prefixes all the time, and for most stuff you won't be changing the order of magnitude too much. (Major exception, pK-whatever)
Megaparsec, kilojoules, kilo electron volt,... are all very common.
Then on the other hand, giga solar masses is never used.
Kilo translates to thousand. Mega to a million. So in you example, kilometer fits perfectly. Megameter would be a million meters, or a thousand kilometers which is annoying to say on the scale we humans use on a day to day basis. And if it comes to space, megameters are way too little.