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Antithesys t1_j20kyi8 wrote

Well, as a matter of fact, astronomers typically prefer the parsec over the light-year. A parsec is derived from the AU, is equal to 3.26 light-years, and is defined as the distance an object would have to be from the Sun to experience a parallax angle of 1 arcsecond (that's obviously not ELI5 but it's a digression).

The AU is better than the light-minute because the AU is a distance that we can easily understand. 3 AU is "three times the distance from the Earth to the Sun." I can wrap my head around that. What is 24 light-minutes? How far is a light-minute? You can tell me the equivalent in miles or kilometers, but the number is so big I can't conceive it as easily.

We can't easily conceive a light-year either, but when we get to distances larger than our solar system there isn't any easier measurement that we can grasp because it's way too far out of our range of human comprehension. The parsec doesn't help, and saying "thousands of AUs" doesn't help. We had to pick one, so we went with the measurement that sounds like it's a measurement of time and confuses everyone.

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autoposting_system t1_j20o98u wrote

Have you guys tried "kajillions of miles"

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Farnsworthson t1_j20szty wrote

As opposed to "parallax second"?

(I'd say more, but I have a deliver to go do on the Kessel run.)

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TheLuminary t1_j20r0gr wrote

I wish we would have just embraced the metric system the way that computers have.

For example 1AU is approximately 150 Gm (Giga-metre)

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Amazingawesomator t1_j20s0gx wrote

You say this, but many people don't know the difference between MiB and MB, GiB and GB, etc.

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Kethraes t1_j20xc7a wrote

Easy.

MiB is Men in Black, MB is Manitoba.

GiB is when you want someone to give you something, and GB is Grand Britain.

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TheLuminary t1_j20tdtp wrote

I think that the practical use for the knowledge of the difference between a MiB and a MB, is much more limited than the knowledge of the difference between a M and a G.

Thus, even if they don't understand that MiB is 2^20 and that MB is 10^6, they will understand that Gx is near enough 3 orders of magnitude larger than Mx. Which in the case of stellar distances, is good enough, IMHO anyways.

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atomfullerene t1_j20wn41 wrote

Huh, I'd never really noticed before how heavily non-metric distance measurements in space are.

I think the reason is that the benefits of metric come from convertibility. Metric's really handy if you need to estimate the mass of a cubic volume of something, or move between mm and km, or get the amount of energy needed to move some mass some distance.

But in space, your distance measurements are all just distance. You aren't using them with other units, typically, so there's no real drive to make them metric. Instead they stick to the older method of using measurements that are convenient for the particular specific context they are being used in.

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TheLuminary t1_j20xe4d wrote

Yep, that makes sense to be. I am still on team make it all metric though haha.

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_OBAFGKM_ t1_j20zyl4 wrote

metric is actually fairly arbitrary. AU and pc are so much more useful in astronomy because they're derived from actual physical quantities that affect the measurements we make. it's so so easy to write down fundamental astronomical equations in terms of parsecs, whereas if you used metric you would need to include some sort of conversion factor

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TheLuminary t1_j21hatm wrote

I guess so.. but AU doesn't even make sense. Considering the Earth does not have a constant distance from the Sun. So don't you still need a conversion factor somewhere?

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_OBAFGKM_ t1_j21mqnz wrote

it's defined as the average distance

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TheLuminary t1_j2242yx wrote

This feels like a Pi vs Tau argument. Constants can be moved around in equations and units can be changed if enough people wanted.

I get why they don't change now, but I wish they would have. /shrug

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_OBAFGKM_ t1_j226apu wrote

It's not really like that, since tau and pi only differ by a factor of 2.

A useful equation is, for example d = 1/p, where distance is measured in parsecs and p is measured in arcseconds. If you used meters, it's not just a factor of 2, it's something like 3.086×10^(16) d = 1/p. With distances as big as parsecs, there's no intuition you can use to understand the size, so it really doesn't matter what unit you use. It just makes the most sense to use the natural unit instead of the arbitrary one

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TheLuminary t1_j226tz5 wrote

Ah.. yes, I suppose having custom units for those specific equations where the constant is 1 would be handy.

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Future_Club1171 t1_j214zy7 wrote

I mean just like imperial, the units are based on SI which is mostly metric. Anything SI with distance can and is defined in meters. It’s just that using meters to convey such quickly gets messy since the universe isn’t going to make everything near round numbers. To give you a fermi approx of an AU, light takes 498 seconds to reach earth, light travels at 2.998x10^8 meters/second, therefore 1 AU is approximately 1.5x10^11 meters, that’s 150 gigameters, note the earth is only 40 mega meters even by the original meter definition.

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