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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."
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...
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."
I'm more concerned about the fact that the distance changes depending on where we are. That means that the Earth is moving, and I don't believe in that. It's more heliocentric non-sense by the astronomical community. What next; astronomical bodies that aren't perfectly spherical? The madness of the commoners, I tell you.
#fuckbeta #iamslashdot #dicemustdie
Since the Earth's orbit around the Sun is eliptical it's _never_ the same, is it?
Have gnu, will travel.
Great, everyone in Eve is going to be missing jump gates, plowing through asteroid fields at warp. Going to be chaos.
No need for snarkiness Dr. Your last sentence was wholly unnecessary. For all you know the AC's a 6th grader still learning the ins and outs of Newtonian physics. Or maybe it's someone with a PhD in something you know nothing about.
Can someone come up with some sort of foot ball field to AU conversion chart or something?
Google still says: 1 Astronomical Unit = 149 598 000 000 meters 1 Astronomical Unit = 8.79057469 × 10^10 smoots
Why should they "mesure" it in miles? Metric is standard.
But to answer your question:
92,955,807.3 miles
- "Scientia non habet inimicum nisp ignorantem"
Dr. Tom's sense of self-importance is bending space around him. Be careful you don't get sucked in. Once you cross the ego's event horizon, not even snarkiness can escape.
92,955,807.273
... because it's not an SI unit.
I know it's a bit out, but I'd go for 149,896,229,000m - exactly 500 light-seconds.
systemd is Roko's Basilisk.
Now when I read an article about an Oort cloud object 10,000 AU from the Earth, I'll know to scrub off that extra 2000 km from my mental model.
I swear to God...I swear to God! That is NOT how you treat your human!
I mean, how many Libraries of Congress is this new measurement?
If telephones are outlawed, then only outlaws will have telephones.
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!
What does the mass of the Sun have to do with the distance between the Sun and Earth?
Good grief! I'm having flashbacks to the lectures about units from my physics teacher!
The more massive a body, the stronger the gravity. The stronger the gravitational field, the closer Earth will end up to the Sun for a given speed (the Earth's speed in this case being more or less a constant. I'm simplifying since the Earth speeds up and slows down as it orbits, but the point is still the same). Likewise, with less mass the Earth will end up farther away.
Also relativistic effects, but those are (probably) a lot less pronounced.
"None can love freedom heartily, but good men; the rest love not freedom, but license." --John Milton
* Golf Clap *
I drank what? -- Socrates
Now that it's "Fixed", it's technically an Astronomical Eunuch.
... lengths of football fields. Or school buses lined up end to end. Or number of King Georges standing with arms out stretched touching finger tips to finger tips stretching all the way from the center of Earth to center of Sun. That is the kind of units that makes sense. Not this convoluted French thingies that we don't even agree on the right way to spell, meter? metre? what the hell?
sed -e 's/Chuck Norris/Rajnikant/g' joke > fact
Or more correctly, units of c times the period of "radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom". Let's get this down to fundamentals and not muck about with intermediate convenience units like "meters".
Here, just for you :)
Forward takes you out, out takes you back, back takes you in, in takes you forward.
I drank what? -- Socrates
Cool, what is it in furlongs per fortnight?
You haven't heard of Metric prefixes?
Those *are* SI units with standard prefixes.
May Peace Prevail On Earth
We can rest easy now.
Where's my sock? There it is...
Almost as much as I love speeding to work in the morning @ 0.000000032 parsecs per leap year.
Excuse me, I'm going to go cook my lunch @ 69 million Joules per day.
Miles? Pffft, I want to know the distance in smoots!
If you're talking about gravitic attraction between two bodies, you *could* be 3 kg of attraction away from something.
Kerning adjustment would have taken care of it.
Nobody takes the trouble anymore...
Dave
If the distance is going to be bouncing around for various reasons it sounds like it isn't a good measurement. Personally I've always liked using light second as a measurement.
Most material objects we want to measure fall into a range where a meter long bit of one, or a cubic meter of one, is very unlikely to have a mass expressed in mere grams. For every person who measures, say, the mass of water in a cubic meter of cloud, or something else where the answer is on the order of grams or tens of grams, there are probably about 10,000 measurements and calculations being made where the answer is likely to be in the multiple Kg. range.
Plus, when the French developed the metric system, a whole lot of the exceptions were totally unknown to them. Modern scientists may be calculating the mass of a cubic meter of dwarf star matter, or how many atoms are in a cubic meter of interstellar space, but the inventors of the metric system probably had no idea at all that the system would need to be extended to such purposes. They did know the system was supposed to be useful for such common calculations as designing a modern sewer system, figuring out how many truckloads of dirt needed to be hauled away from a construction site by both the maximum volume and maximum load weight per truck, or inventorying a bin of bolts by sample methods, and other such commonplace tasks.
The very fact that so many people use the abreviation mks, or that both of us recognize it easily, says that the fundamental units, before prefixes, are poorly chosen for compatability. If the base units came up frequently together in measurement and calculation,.people would have stuck to using those base units together in the common name, and mks would sound odd.
Who is John Cabal?
How can mass units be "orders of magnitude out of scale" with dimensional units?
That's not even an apples-to-oranges comparison - at least those would both be fruits. Comparing mass and distance is literally nonsensical. What? Are you 3 kg away from me?
Mass relates directly to distance, since 1 liter of water (volume of a cube 0.1m on each side) is approximately a kilogram. Alternately, 1 gram is approximately the mass of a cube of water 0.01m on each side; this was, in fact, the original definition as decreed by the French government.
If the French had chosen the mass of 1m^3 of water as the standard then the unit of mass would be in-scale with the units of distance and volume. In a system like that I could estimate my volume by simply stepping on a scale and reading my mass; the same number would be both my mass and volume, just change the unit label. Instead they chose a system where the volume of the definitive unit mass was 6 orders of magnitude away from the unit volume. As if to confuse matters more, the standard volume unit (liter) is 10^3 smaller than the cube of the unit length and (if holding water) has 10^3 larger mass than the unit mass.
If you don't care about this, that's fine; neither did the French. They cared more about the units being useful on their own in day-to-day life, and were happy that there was an even factor of 10 difference between the scales. The historical fact remains, though, that the French knowingly chose not to unify their units when creating the system, presenting modern geeks with the first-world problem of needing a conversion factor between mass and volume rather than the units being strictly 1-to-1, and affording them the opportunity to complain about it. Just because the complaint is pointless doesn't make it wrong ;^)
"Space Exploration is not endless circles in low earth orbit." -Buzz Aldrin
Don't mix speed and distance.
Hey, I can do the Kessel Run in 17 parsecs!
Google does the conversion if you ask, but it's definition of AU is rounded off. Google "1 au in smoots".
Actually if you printed out one dollar bills for the national debt it would go about 10 AUs at this point... Or you could do 1 AU with 10 dollar bills.
(155.95 / 1000) * 16 027 000 000 000
Yes it's an anecdote! Were you expecting original research in a Slashdot comment?
I thought the plural of Smoot was Smeet!
92,955,807.3 miles
"And that's why it looks so small."
Ceci n'est pas un sig.
You haven't heard of Metric prefixes?
Those *are* SI units with standard prefixes.
Of course he has. And the gram is not the SI mass unit, the kilogram is:
Despite the prefix "kilo-", the kilogram is the base unit of mass, the kilogram, not the gram, is used in the definitions of derived units.
Nonetheless, units of mass are named as if the gram were the base unit.
Neither the MKS nor the CGS metric system variant is consistent in this way; one uses a "kilo" prefix on the base mass unit, the other uses the "centi" prefix for its unit length. The AC you're responding to would probably be happier using the MTS variant.
His complaint may be of a first-world problem, but he's not wrong.
"Space Exploration is not endless circles in low earth orbit." -Buzz Aldrin
For some reason the first thing i thought of was this:
http://xkcd.com/927/
Which is only partially true... but lets face facts, there is a TONNE of old doco out there that'll depend on outdated AU measurements, so for decades astronomers will still be going "which AU unit are they using" (something engineers still deal with on a daily basis)
There's no point in a unit (AU) being a large multiplier of another unit. We have an entire metric system for that (well, some of us do). The nice part about AU was precisely that it represented something dynamic. I don't always care how far away some asteroid is to the metre. I want to know how far it is relative to the sun.
You do realise that fuel efficiency in cars is measured in square metres? Unit cancellation is wierd. Oblig/Ref: according to my graph xkcd will produce a cartoon to answer a /. post in advance within six months.
Please consider this account deleted, I just can't be bothered with the spam anymore.
I know a dude who did it in 12.
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I'm sorry, but I don't know what a mile is. And since my brain is hard-wired to the SI system, it's impossible for me to know.
...Now fix the kilogram.
1602 metres (to use the CORRECT SPELLING).
Operation Guillotine is in effect.
depends what it's made of (foam rubber or neutronium?) and where you are measuring it (an object weighs 2.36x more on Jupiter than it does on Earth. The same object weighs 27x more on the Sun than it would on Earth. Its mass would be the same).
The SI unit of weight is the Newton. This is defined as the contact reaction-force against the force of gravity, for an object at rest on the ground. For a solid object with a mass of 1 kilogram, weight is equal to 9.80665 Newtons.
Incidentally, the outward force (centripetal acceleration) imparted by the spin of the Earth means that the weight of an object at rest is slightly less at the Equator than it is at either Pole. Such observation is proved by the slight equatorial bulge of the Earth caused by the same outward force.
Operation Guillotine is in effect.
are we talking about a cloud of condensed water vapour, a cloud of droplets, or a cloud of steam?
For the last, that's easy: any gas at ground level and standard temperature and pressure has a density of 1 mol per 27 cubic metres. For monatomic oxygen, that's approximately 16 grams of gas in a fairly large room.
For the others, pick a number out of your arse, that's probably as good a guess as you're gonna get.
Operation Guillotine is in effect.
Always nice to see another Niven fan.
-- Alastair
Interesting but then depends on measurement of c and timing of a second.. whereas the standard length of measure is a meter.
Still, you could call 1AU == 150 gm == 500 lightsecs
I just read the wiki entry on the Smoot, made me chuckle. Amazing how a college prank can live on such as it has.
Operation Guillotine is in effect.
I assume you'll be surprised that for many people, weigh means: to hold up or balance, as in the hand, in order to estimate the amount of mass;
Or on a wii-fit challenge :)
I know a dude who did it in 12.
Don't believe him. He's just messing with your head.
Really I think a nice round number like 150GM that's 'giga meters' that would be much nicer and easy to remember
By the way your argument about being able to choose any gas and compress it is interesting, but it doesn't even match history. Nobody ever used compressed gas as a reference for mass, AFAIK.
As log as you're using SI units giga will always be 10^9.
Well, when the name invented by a nine-year old child for a certain large number can end up, slightly modified, as the name of one of the major companies of the internet which everyone has heard about, then a college prank living on on some Wikipedia page and as a feature in a calculator which incorporates a lot of jokes (ever wanted to know what 2^(the answer to life, the universe and everything) is? Just ask Google!) doesn't look that amazing to me.
The Tao of math: The numbers you can count are not the real numbers.
My balls cause gravitational lensing.
That's because they are black holes: Nothing ever leaves them.
The Tao of math: The numbers you can count are not the real numbers.
It doesn't depend on measurement of c because SI fixes c at exactly 299792458 meters per second.
It does depend on the second, but the current definition does, too, because the meter is defined as 1/299792458 of the distance the light travels in vacuum during 1 second (this definition is what fixes the speed of light). In other words, the meter is defined to be 1/299792458 light seconds.
Which in turn means that the astronomical unit is now de facto defined to be exactly 1024642950/2053373 light seconds
The Tao of math: The numbers you can count are not the real numbers.
If it's 93 million miles to the sun, then a number around 149 million meters is far too short. ...should read KILOmeters...
Or 149 billion meters.
The Tao of math: The numbers you can count are not the real numbers.
Definitely one of the timeless ones (they do need to freshen the paint on the bridge though, it's been fading recently).
I always love visiting the MIT campus, you'll never know what you might find. I try not to gawk at the students, although sometimes they gawk at me since I look like a 40 year old student of MIT.
You can see more hacks in the gallery.
http://hacks.mit.edu/Hacks/by_year/
touché.
Operation Guillotine is in effect.
Ooooohhhh.... Snap.
Kendy for the state...
Not everything that can be measured matters; Not everything that matters can be measured.