You give astronomical distances beyond the solar system in light-years, but professional astronomy papers use parsecs. Which is preferable?

Trigonometric parallax determines the distance to a star by measuring its slight shift in its apparent position as seen from opposite ends of Earth's orbit.
Bill Saxton, NRAO / AUI / NSF

Light-years, no question! Here’s how I see it. The parsec (which equals 3.26 light-years) is defined as the distance at which a star will show an annual parallax of one arcsecond. This means it is based on two arbitrary quantities: the radius of Earth’s orbit, which was a random accident of how the solar system fell together, and the definition of the arcsecond — an even more arbitrary unit that stems from the ancient Babylonians’ base-60 style of arithmetic, along with their notion that the circle should be divided into 360 degrees because there “ought to be” 360 days in a year. The light-year, by contrast, is based on only one arbitrary value (Earth’s orbital period) and on a fundamental constant of nature: c, the speed of light.

Moreover, as a practical matter, few distances in modern astronomy are directly measured by the parallax method anymore. However, it’s often important in modern astrophysics to know the light-crossing time of a given distance — and if the distance is given in light-years, there you are.

— Alan MacRobert


Image of kazvorpal


October 19, 2018 at 9:24 pm

One significant flaw in this argument is that base 60 is slightly LESS "arbitrary" (as you're using that word) than base 10. There is nothing scientific, nor objective, about our base 10 system. We use it because we're monkeys that need to learn to count on our fingers, not because it's in any other way effective.

Base 60 is much more objective and potentially useful as a radix.

The most objective would be binary, followed by any power of 2. We'd be better off with base 8 or base 16 than with base 10. But base 60 comes in well before base 10 on the list of potentially useful systems.

You must be logged in to post a comment.

You must be logged in to post a comment.