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Comment by drekk | Hacker News Reader

They're not. We're saying the non-SI unit of light years shouldn't be used over something like petameter. Just multiply the "light year" measurement by .9461 and you're set. Or, ideally, just measure in SI units to begin with? The US is the holdout here and for no good reason

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The US isn't the holdout. Astronomers everywhere use light years and parsecs. Particle physicists everywhere use barns. Chemists everywhere use Angstroms.

Astronomers also use angstroms when refering to the filters used for solar observations.

Just because they're pretty, here's a link to the SDO gallery: https://sdo.gsfc.nasa.gov/gallery/main

Also, the SDO takes an image through each filter as it rotates through the filter wheel, IIRC, it takes 15 minutes to rotate through them all. They are then made available for each filter at different resolutions. Being the hacker-ish type, I wrote a script to use curl to download the image sequences for chosen filter/framesize for the sun's full rotation to create a one day timelapse.

And if used literally, parsecs (parallax arc-second) should have smaller values the father away something is!

How long does it take for light to travel petameter vs how long did it take to travel that light year? The light year is something people can relate to

I for one welcome the idea of measuring time in lightpetametres ;)

(that's about 38.6 days for the curious)

The problem is with what a year is, which is arbitrary to begin with, but worse still, a year is not constant. The momentum of every planet is affected by the gravity of every other planet, leading to fluctuations in solar orbital speed, which means a full orbit is likely never the same period as the previous or subsequent orbit. Maybe these fluctuations are small, but light travels so fast that over long distances it is sure to be significant. Thus the definition of a light year is defined as the distance light travels in a Julian year, 365.25 days, but this just pushes the error down to a different measure, because days are not constant either. Since the speed of light actually is constant, maybe we should define years and days by the speed of light instead of vice versa.

Of course, there's also the problem that a light year is only relevant to someone from Earth. A light year for a Neptunian would be drastically longer, let alone someone extra-solar system to us

Shush pedant and relate to things with the rest of us using stuff we already understand

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