Measuring Speed

It occurred to me today that with the world getting faster (Virgin Galactic were showing off their new passenger craft) we don’t seem to have many ways for covering the new description of speeds. For cars we go with miles or kilometres per hour, even aircraft use it. For fast aircraft we use mach (the speed of sound) but this is different depending on air temperature and altitude so it’s not a good standard to use. So when we have machines travelling at 1000 km/h or more, or covering inter-solar distances, we’re going to need some new standards.

Relative distances seem to be covered by the following standard measurements:

Distances to satellites kilometres
Planetary distances astronomical units
Distances to nearby stars light years, or parsecs
Distances at the galactic scale kiloparsecs
Distances to nearby galaxies megaparsecs

As it turns out there are quite a few larger distance measures already available in the metric system:

1,000 km = 1 megametre (Mm)
1 million km = 1 gigametre (Gm)
1000 million km = 1 terametre (Tm)
1 petametre (Pm) (9.46 Pm = 1 light year)
1 exametre (Em) (100 Em = 10,000 light years)
1 zettametre (Zm) = 100,000 light years or 50 kiloparsecs
1 yottametre (Ym) (2 Ym = 200 million light years or 60 megaparsecs)

Although, to be honest, the phrases he was doing 80 exametres per hour and it’s got a top end of 100 gigametres per hour doesn’t exactly roll off the tongue. We could probably do with some more catchy measures.

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