Thanks to wikipedia

10,000,000 Kilometers is equivalent to

10,000 megametres... which is equivalent to

10 gigametres... which is equivalent to

0.01 terametres

Distance from Earth to Saturn is

1,321,416,800 Kilometers

1,321,417 Megametres

1,321 Gigametres

1.3 Terametres

ok, my math is probably off, I might be removing an extra zero or two (please if you notice post so I can correct).

To me it sounds like "Gigametres" is the way to go for long distance space travel (travel between planets). Megametres is still to long to say and terametres is too short.

Also, I don't like how Megametres would sound to the reader ("One Million Five Hundred Thousand Megametres" vs "Fifteen hundred gigametres")

The problem I'm having is using this in writing. Does the average reader know what a gigametre is? I feel the need to slip the definition of a gigametre into the story so the reader is not confused. However I don't feel like going 50's sci-fi (Well Jimmy, radiation is the byproduct of nuclear energy...) on the reader.

Thoughts?

[This message has been edited by halogen (edited April 26, 2008).]

I'd say use gigametre. If it matters enough people who don't know they will look it up.

I tend to avoid distances in my scifi unless I have to have it. It really has little relevance to most readers. When I get into my car to go somewhere, I think in terms of time it will take to get there over the actual mileage it is. If you are leaving planet one and going to planet two, does it add to the story to say "54 gigameters"? Or would, "about two days", be quicker to understand?

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The Parsec is a pretty standard measure. For more local distances, you could go down to milliparsecs.

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Hrm...

1 Parsec = 31,000 terameters...

that means...

1 Milliparsecs = 31 terameters

That means the distance from Earth to Saturn is

0.000042 Parsecs
or
0.042 Milliparsecs

But, as River says in an episode of Firefly (or was it Serenity?), "She understands. She doesn't comprehend." Whether "fifteen hundred gigametres" would be meaningful to readers is another question. While I know intellectually what it means, it really means little to me: I can't visualise it in familiar terms.

If you measure in AUs, I know we're talking solar system distances. If you use parsecs or lightyears, I know we're interstellar. "Fifteen hundred gigametres" tells me I need a conversion table: despite knowing what "giga" means, I can't visualise it against a solar or interstellar framework.

Maybe, instead of fifteen hundred gigametres, use fifteen hundred mega-kilometres, or mega-klicks, thus retaining a relationship with the familiar "km" measure of large distances.

I don't think I'm alone in being unable to visualise distances. This is why newspapers tend to measure things in terms of football pitches, or here in England, London buses. ("The bridge soars over the river in one span. It's the length of a hundred London buses and wide enough to take six abreast.")

As Lord Darkstorm says, we often measure large distances in terms of travel time. When people who are unfamiliar with England's geography ask where I live, I tell them Derby, some three hours drive north of London. I imagine it may be the same in your stories--we won't know the local geography.

So although I believe SF audiences will know what giga- and tera- mean, I'm not sure such measures will convey the sense of distance to the reader.

Earth is eight light minutes away from the sun. Pluto is like a light hour from the sun. There are several seconds to the moon. for space travel, light speed is thought of as a constant.

Consider a ship that can travel a hundred light years in a month. It suddenly runs into problems and now travels a light hour in a month. just knowing the time to travel gives a lot of information to the crews and the reader.

In traveling across country, how long it took to travel a distance was more important than the actual distance. Going over the pass, rather than following the river, might be ten times shorter, but if it took equal amounts of time to go to the same destination, one knows how difficult the pass is to cross.

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That seems like a hard number to operate with. When you say the Parsec is standard do you think it was used for something like the Huygens mission (referencing how far away the Huygens is, how much farther to reach the next target, etc)?

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By standard, I meant a commonly used astronomical term--so maybe better adapted to distances in space than terrestrial units. I've no idea what NASA uses. I'd be interested to find out if anyone happens to know; feet and inches would be my guess!

I've seen parsec used a bit in sci-fi, probably because its a single word that rolls off the tongue quite well.

For stellar rather than interstellar distances, the au would work well and avoid the need to mess with milli / micro parsecs.

My understanding is that both au and parsec are based upon the earth's orbit. This might not be baggage you want to carry into an alien culture. In that case, the light-year would be another way to go.

basic geometry:
length of arc = radius * angle

If you wish for the length of the arc to be one au (astronomical unit) and for the angle to be one angular second (meaning 1/3600 part of a degree - a whole circle has 360 degrees so 1/1296000 part of a whole circle), then the radius should be one parsec.

Turn the equation:
radius = length of arc / angle

Input the angle in radians, meaning 2*pi/1296000, input 1 au = 146 000 000 000 meters and you get 1 parsec = 30114661712076067 meters. Divide this number by 365, then by 24 and 3600, then by the speed of light 300000000 and you get roughly 3.18 light years for a parsec.

http://coolcosmos.ipac.caltech.edu//cosmic_classroom/cosmic_reference/distance.html

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10,000,000 Kilometers is equivalent to

10,000 megametres... which is equivalent to

10 gigametres... which is equivalent to

0.01 terametres

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In case anybody cares,

0.01 terameters is equivalent to

0.00001 petameters ... which is equivalent to

0.00000001 exameters.

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You'll see petabyte hard drives within fifteen years.

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