They just need to get use to the larger prefixes like everyone else and stop using non-coherent units like light-year.
Jerry ________________________________ From: John M. Steele <[email protected]> To: U.S. Metric Association <[email protected]> Sent: Sunday, March 29, 2009 1:23:01 PM Subject: [USMA:44201] Re: The speed of light Astronomers tend to give the distance in lightyears or parsecs however (the real data is parsecs based on what they actually measure). My real point was that the distances are not known accurately, and the errors increase with the square of distance. Only the two closest stars are known to better than 0.01 lightyears. By distances of 15 lightyears, uncertainly is around 0.1 lightyears. That simply can't lead to precision navigation. --- On Sun, 3/29/09, Jeremiah MacGregor <[email protected]> wrote: From: Jeremiah MacGregor <[email protected]> Subject: [USMA:44193] Re: The speed of light To: "U.S. Metric Association" <[email protected]> Date: Sunday, March 29, 2009, 11:00 AM Light year is not an SI unit so I doubt it would be a unit used in navigation. The units you would use are the ones that have the support and care of the standards institutions, like the meter and the second. Light years were invented to give mile users a larger unit as it becomes difficult to have to write so many zeros. With SI you don't have that problem. You simply use peta, exa, zetta and yotta to eliminate the use of the zeros. Of course you have to get use to using the names first. Jerry ________________________________ From: John M. Steele <[email protected]> To: U.S. Metric Association <[email protected]> Sent: Sunday, March 29, 2009 10:42:35 AM Subject: [USMA:44190] Re: The speed of light In my opinion, roundoff would be FAR less than our uncertainty in ANY interstellar distances. They are only known approximately. While a "light year" is about 9.46 Pm/a (depending on which "year" definition you use), that could probably be rounded to 10 with no great harm. Much like sea travel, you would have to frequently recalculate based on new observations. --- On Sun, 3/29/09, Jeremiah MacGregor <[email protected]> wrote: From: Jeremiah MacGregor <[email protected]> Subject: [USMA:44184] Re: The speed of light To: "U.S. Metric Association" <[email protected]> Date: Sunday, March 29, 2009, 9:28 AM Yes, you are right. I fixed it below. But either way the number in miles still never ends. I wonder what effect that would have if one was traveling to a distant galaxy using miles.. Would the round off errors cause a problem in locating the planet? Jerry ________________________________
