I recall in the early 90s when the US government weather service changed all their official observations from F to C. Which meant the entire US aviation community had to adapt to air temps and dew points available only in C. All delivered in the international standard terse computerese that bore little resemblance to the US standard terse computerese it replaced. Lots of hilarity ensued.
We still get all our data in C and mentally convert it to F for delivery to the US passengers.
Wow. It’s even crazier than I realized. Thank you.
Why do we still use “light-years” for interstellar distances? Why not 9.7 petameters instead of 1 light-year?
Canada is a big country, but it only seems like it’s lightyears across.
I’m only a hobby astronomer, but my impression is that in academic research, interstellar distances are more often measured in parsec rather than lightyears.
That’s right, but they’re converted to lightyears for popular science articles. People intuitively understand lightyears[*], not so much parsecs or (even worse) petameters.
[*] OK, no one really intuitively understands lightyears, but people think they do, and that’s good enough.
“Petameters” or what have you doesn’t really convey information in any useful way that LY doesn’t. I’d argue light years is actually the superior term just because it at least conveys the immensity of the distances involved.
Expressing it in petameters also implies a degree of certainty we really don’t have. Even for prominent stars, except for the closest ones, the distance is just an approximation.
I think the “no one really intuitively understands lightyears” bit in your footnote explains why astronomers are not using petameters. Interstellar distances exceed the distances that we can intuitively relate to by so many orders of magnitude that there is not really much of a need for integrating them into the system of measurement we use for everyday life.
Now, for distances within the solar system, popular science publications will frequently use miles/kilometers, whereas serious astronomers usually prefer AU. So even here there is little effort to apply the usual distance units to the astronomical scale.
HGV stands for Heavy Goods Vehicle, but although still commonly used, O (for ordinary) GV is the legal descriptor.
Vehicles here are classified as:
Each class has a different driving test and licence. Everyone starts with a car licence which can be obtained at 17, and if they want to drive trucks they have to work up to LGV and then OGV. PSV licences are separate and a licence to drive a 44 tonne semi is not a licence for a bus.
Believe it or not, it’s actually a lot more complicated than that.
Thank you.
The US system is broadly similar. And yes, lots of complexities hide in the corners of what looks like it ought to be just a simple hierarchy of weights.
You don’t see the point of having a temperature scale that has universal (save the wisassery), empirical set points? What you feel is a better reference?
One of the perennial sources of amusement to non-Americans is how a vast nation with dozens of climates still sticks to a temp system based on what an ancient Dutch bozo thought were cold and hot conditions in his tiny, far-flung homeplace.
From Paul Rush, the morning radio host in 1974:
Zero is freezing
Ten is nothe 4% difference between th5e itmperial and US ounce explains why the first time I came to Canada, there were signs on the gas pumps explaining to Murricans that 5 of our gallons are equivalent to 6 of yours (instead of the expected 4 to 5).
Even the people who think that the lightyear is a measure of time think that they intuitively understand the unit.
Maybe, but the nose gear wasn’t down and locked without hydraulics. Where they lined it up on the barricade helped it slow down.
The pilots did a hell of job just getting the plane on the ground.
The other day I used the idiom “missed by inches” and it reminded me that there are a number of non-metric idioms that don’t really have a good metric equivalent (e.g. “missed it by a mile”). In particular, I always feel awkward saying “give someone a centimeter and they’ll take a kilometer” to my wife.
I’m pretty sure that when the U.S. more fully adopts the metric system, that the winning run will forever and always be 90 feet from the plate.
(Liters of soft drinks, grams of fat, 5k races, kilowatts of electricity, metric busloads [or whatever] of nonsense… we’re partway there.)
There’s a practical reason (well, a few practical reasons) why distances within the Solar System are measured in AU instead of anything metric. When we first started measuring the Solar System, it was easy to get very precise ratios of distances, but very difficult to tell any of the distances absolutely. Kepler, for instance, was able to say that the orbit of Mars was 1.542 times as large as that of Earth, but had almost no clue of what the radius of Earth’s orbit was in any Earthly units. And even after good measurements of absolute distances started coming in, the relative distances were still even better known. So by working, as much as possible, in AUs, you could work to much greater precision than by working in meters.
Oh, and also, by using the radius of a planet’s orbit as a length unit, and the period of that same planet’s orbit as a time unit, you can make the proportionality constant in Kepler’s Third Law come out to 1, which is convenient. And we already have a standard unit for the period of one planet’s orbit, that everyone is familiar with.
Good post/username combo. Another (silly) point to make is that minutes, hours, days, and years are not metric units; only seconds are truly metric. Which demonstrates something, but I’m not sure what.
Just as the length of a wicket will always be one chain (22 yards)
I haven’t heard mention of that scale in ages. It is what we used in the US Navy nuclear power program when I was in.
In Nuclear Power School, everything was done (painfully) in Imperial units, including thermodynamics calculations. All kinds of references to Rankine, BTU, horsepower, and other things not well suited to scientific calculations.
Our physics calculations all used lbm and lbf (pounds mass and pounds force) as well as a proportionality constant that converted between the two that had to be salt and peppered throughout familiar physics formulas.
I certainly hope Navy Nuclear Power is metric these days.
Side note: my favorite unit from that training was the barn, used to measure areas of cross section at a subatomic level, such as measuring the apparent area presented to a speeding neutron by a nucleus. The term comes from “couldn’t hit the broad side of a barn”