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Astronomers Fix the Astronomical Unit
gbrumfiel writes "The Astronomical Unit (AU) is known to most as the distance between the Earth and the Sun. In fact, the official definition was a much more complex mathematical calculation involving angular measurements, hypothetical bodies, and the Sun's mass. That old definition created problems: due to general relativity, the length of the AU changed depending on an observer's position in the solar system. And the mass of the Sun changes over time, so the AU was changing as well. At the International Astronomical Union's latest meeting, astronomers unanimously voted on a new simplified definition: exactly 149,597,870,700 meters. Nobody need panic, the earth's distance from the sun remains just as it was, regardless of whether it's in AUs, meters, or smoots."
if politicians can be SD-conservative, why can't astronomers? we all know that significance is precious and rare...
It was decided by committee. I'm sure it was a compromise of several possible values, with concessions on each side, a few attempts to filibuster it until Pluto was given recognition again, etc. No, I'm not trying to be funny.
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Since the Earth's orbit around the Sun is eliptical it's _never_ the same, is it?
Even an elliptical orbit is right twice a year.
Have gnu, will travel.
you'd think they could have rounded up to 150 gigameters.
if politicians can be SD-conservative, why can't astronomers? we all know that significance is precious and rare...
Interesting point.
If you are going to pic arbitrary number, why not pick an easy one?
I suspect there is a desire to keep all past references to AU meaningful within a small margin of error, so as to not have to translate any written works.
The difference between the new arbitrary number and the prior imprecise one is probably infinitesimally small for the scale of reference AUs are use for.
Rounding it up almost half a million kilometers (quarter million miles) maybe not so much.
I suspect that since it was imprecise in the first place, and used for almost nothing except astronomical reference, preserving existing references in the literature was more important than the ease of writing it down.
Sig Battery depleted. Reverting to safe mode.
92,955,807.3 miles
Your answer is SOO 8 minutes ago...
I swear to God...I swear to God! That is NOT how you treat your human!
This is correct. originally the AU was defined as the average distance between the Earth and the Sun. The problem then was to convert this distance to meters. The way to do this conversion in the end involves the product of the mass of the Sun and the Gravitational constant G. Both quantities are not well known (e.g., G is known to 4 or 5 digits only). But their product can be determined from modeling the motions in the Solar system to much higher precision. So by that time the AU was then redefined by defining the product GM (often called k^2, where k is called the "Gaussian gravitational constant"). It is my understanding that this has now been simplified. The difference between both is only a few meters.