h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

It seems to me that this "astronomical unit" is rather small when compared to the distance between one system
and the next. I believe that I'd find it just as hard to comprehend that, say, Alpha Centauri is X(and that's a big
X!) AU from the sun. Therefore, not being an astronomer I ask in ignorance, should there not be a more
manageable measure of distance for outside our own solar system? I'm sure that there is, I just have no idea
what it is or what it's measurement is.

Surely the measure you ask for is the light year - the distance light travels in one year. Not that I'm any expert.

Correct! One light year is almost 6 trillion miles! I think the nearest star is 4 light years away. But I am not an expert either.

Or evan the parsec,

Eight light minutes = 1 AU.
Alpha Centuari is 4 light yrs away. (I think)
Therefore I make it about .5x60x24x365=262,800 AU to Alpha Centauri. Give or take.

Surely the measurement should be to the 11 m, not 13 cm?

You see, that's the problem! I understand AU. Very simple: AU= the distance from the earth to the sun. But
then we get into light years. Why should I, the every day schmoe, give a damn about how long it'll take for light
to travel to a given point. I can't move that fast, and I doubt you can either! I would rather know how far, in miles,
without having to do a whole bunch of calculations, how long it'll take me and my '73 pontiac to get to the nearest
solar system. That's right, I want miles. Granted, I'm just playing devil's advocate here, but I fail to see the point
in taking a measurement that has a set value, and taking out of context to apply it to a completely unrelated
topic. Then, to make matters worse, we use that unrelated topic as the basis for measurement thenceforth! I
am, of course, talking about using the "speed of light" to put into manageable terms "universal measurement.
Just a rant, I apologize for sounding like a lout.

Yeah, but what is easier? 4 light years as compared to 4 million, or a couple of billion miles to a couple of trillian?

Personally I think it's pretty impossible to put universal distances in human terms no matter what units you use - yes, we can't imagine what it's like to travel at the speed of light, but even if we could, we couldn't imagine doing it for 15 billion years or so. Just accept the light-year, and keep reminding yourself that your pontiac is a hellofalot slower than light.

And there really is a correlation between the light-year and the things astronomers look at. Knowing the distance in light years tells us how old the image is we're seeing in the telescope. We see the Andromeda Galaxy as it was 2 million years ago, because we've figured out it's 2 million light years away. We see younger-looking galaxies the farther away we look. Very handy for people studying how galaxies change over time, and nobody has to deal with any messy conversion figures, like certain NASA engineers I could name .

In fact the first person to ever measure the speed of light figured it out because he predicted the moons of Jupiter to hide behind the planet at a certain time, but a few months after he made the predictions, he found the moons were several minutes off. Turned out he didn't know that it took the light from Jupiter several minutes to cross the extra distance from one side of Earth's orbit to the other.

(sorry for sounding like an astronomer with too much time on his hands... but I am...)

Interesting point Doppleganger - your pontyiac would appear to be a different colour coming towards us, from the colour going away from us if you were travelling anywhere near the speed of light due to the doppler effect. Just as the sound of the train changes tone when it goes past you.

I just want to know what sort of Pontiac Doppleganger has - I've certainly never seen one that could make the trip between Earth and Alpha Centauri. A heavily modified one, I'd guess.

That being the case, I don't see what use miles would be (especially since the civilised world uses kilometres, spells civilised with an 's' and kilometre ending with "re" ). At least for interplanetary distances measured in AUs don't result in lots of uses of words ending with "illion", and broken zero keys.

AU are useless over interstellar distances (as any good field researcher would know), and are only convenient at interplanetary scales; and parsecs are useless when measuring things the size of solar systems.

Hell, it takes a lot to get a VW Beetle cross the pond. [Either that or a RORO ferry...]
Still, we do use meters at both astronomical and atomic distances: just
10e30 m or 10e-30 m...

I must point out that it is basically unreasonable to quote the distance in centimeters rather than kilometers. The AU is 149 million kilometers. Period. Next I suppose someone will recalculate that into Ångstroms !

Why not? 1490000000000000000000 Angstroms, I think. [An Angstrom is about the size of an atom]

Thanks to The Cow I was wondering what an Angstrom was would you like to elucidate?

By all means. The Ångstrom is a unit of length = 10^-10 meters (that's ten to the power minus ten meters), or 0.1 nm (nanometers). It is used for stating wavelengths of electromagnetic radiation (such as light), but is not part of the SI-system (Systeme Internationale, the International System of units, which defines such bacis units as the meter, second, etc.). Thus all the zeros in the previous post are probably correct, but I can't be bothered to count them. That's why we use scientific notation, anyway (such as 10^-10 meters).

The Ångstrom is named after the Swedish physicist Anders Ångstrøm (1857-1910), professor at Uppsala University 1858-74. He worked with heat conduction and spectral analysis and determined the wavelengths of the Frauenhofer lines in the Solar spectrum.

And yes, there should be a ring above the intial A in Ångstrom. This has to do with the peculiarities of the Scandinavian languages, which may actually be worthy of an entire Guide Entry. I just might write that !

How do you type A-rings?

Thanks for the info - being an engineer I use the SI units but I cannot plot anything smaller than about 0.5mm on the drawing board.(That dates me doesn't it?)

What the hell is an AU? Sorry. I wasn't listening.

Please see my new entry (submitted for approval) A233218, 'Peculiarities of the Danish Alphabet' which discusses the A-ring phenomenon in considerable detail.