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What is a "light-year"?


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61 replies to this topic

#1 of 62 David Baranyi

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Posted October 02 2003 - 05:51 PM

While reading an article on the Sombrero Galaxy from hubblesite.org, I read that it is located 28 million light-years from Earth. I like to know: what is a light-year, and how fast would an unmanned satellite will have to travel to reach the nearest galaxy?

#2 of 62 John Thomas

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Posted October 02 2003 - 05:57 PM

Not so much a measure of time as it is distance, it's the distance that light would travel in one year.

"The distance over which light can travel in a year's time; --
used as a unit in expressing stellar distances. It is more
than 63,000 times as great as the distance from the earth to
the sun."

Specifically, it's 5.88 trillion miles or 9.46 trillion kilometers.

#3 of 62 Ted Lee

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Posted October 02 2003 - 06:27 PM

i've always thought the concept of light years pretty cool. kinda neat to think that the light you see from some stars could have been travelling for years and years before it got to you.
 

#4 of 62 David Williams

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Posted October 02 2003 - 08:35 PM

and don't forget we're talking about light speed as expressed as the speed of light in a vacuum.
"Only two things are infinite––the universe and human stupidity, and I'm not so sure about the universe." ––Albert Einstein

#5 of 62 John Watson

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Posted October 02 2003 - 10:06 PM

about 365 times longer than a light day Posted Image

Oh, I gettit! A question for science guys. Sorry!!!

#6 of 62 Kirk Gunn

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Posted October 02 2003 - 10:22 PM

Isn't a nanosecond the time it takes light to travel a foot ? or is it a metre ?

And here's one for the scientists...

Can someone explain, in an "Einstien for Dummies" format, the whole reason you can't travel faster than light speed ? Thanks

#7 of 62 Justin Ward

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Posted October 02 2003 - 10:30 PM

Quote:
Can someone explain, in an "Einstien for Dummies" format, the whole reason you can't travel faster than light speed ? Thanks


I'm not an enpert on this, but I believe it has something to do with idea that the energy required to accelerate an object increases very steeply as you near the speed of light. To go the speed of light it would require "infinite energy". However, from what I understand, it isn't unreasonable for us to someday travel say 90% the speed of light.

#8 of 62 CharlesD

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Posted October 03 2003 - 12:45 AM

To answer the second part of the question, the nearest galaxy to our own is Andromeda which is 2.2 million light years away. It took the Voyager probes more than 25 years just to reach the outer edges of our solar system.

If it took Voyager 25 years to cover 80 AU, then it would take 19,687.5 years for it cover one light year (63,000 AU = 1 light year). Andromeda is 2.2 million light years away so (if it was heading in the right direction) one of the Voyagers would get there in
43,312,500,000 years!

#9 of 62 Mike Wladyka

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Posted October 03 2003 - 01:54 AM

1 parsec equals 3.2616431 lightyears, makes me wonder what is the kessel run is? obviously a distance in which some speed needs to be reached?
Now they show you how detergents take out bloodstains, a pretty violent image there. I think if you've got a T-shirt with a bloodstain all over it, maybe laundry isn't your biggest problem. Maybe you should get rid of the body before you do the wash.

#10 of 62 MarkHastings

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Posted October 03 2003 - 02:04 AM

Quote:
kinda neat to think that the light you see from some stars could have been travelling for years and years before it got to you.
Also the fact that most of the stars you see may have burned out millions of years ago, but we don't know it because we're just getting it's light right now.

Someone once told me to think of star light as ghosts. You are seeing the light of something that could have died years and years ago.


p.s. 9 posts and no mention of Toy Story Posted Image

#11 of 62 AllanN

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Posted October 03 2003 - 02:05 AM

Quote:
Quote:
Can someone explain, in an "Einstien for Dummies" format, the whole reason you can't travel faster than light speed ? Thanks
I'm not an enpert on this, but I believe it has something to do with idea that the energy required to accelerate an object increases very steeply as you near the speed of light. To go the speed of light it would require "infinite energy". However, from what I understand, it isn't unreasonable for us to someday travel say 90% the speed of light.


As I recall, as an object accelerates towards light speed its mass increases, with this increase it takes exponentially more energy to achieve acceleration. Someone with a better background in physics will surely come along and elaborate on this subject, maybe even prove me wrong.
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#12 of 62 Leila Dougan

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Posted October 03 2003 - 02:08 AM

"To infinity and beyond!"

Sorry Mark, just had to Posted Image

#13 of 62 Mike Wladyka

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Posted October 03 2003 - 02:08 AM

Quote:
Can someone explain, in an "Einstien for Dummies" format, the whole reason you can't travel faster than light speed ? Thanks


i think it is possible to go faster than the speed of light, but not sure...here is my reasoning, as you approach the speed of light time slows down, or for that matter traveling at any speed slows down time (i think it was proved in the 70's with a plane and two atomic clocks) So if time slows down you would actually feel that you were going faster than the speed of light. I thought i heard somewhere that traveling at 99% of the speed of light you would age 1 year while people on earth would age 460 years. So if a distance to another a planet was 460 lightyears away you would only age 1 year going at speed of light (rough approximation only) while going to said planet. Of course, most of my info is speculative, so don't attack me...but it is kind of a half ass proof

Mike
Now they show you how detergents take out bloodstains, a pretty violent image there. I think if you've got a T-shirt with a bloodstain all over it, maybe laundry isn't your biggest problem. Maybe you should get rid of the body before you do the wash.

#14 of 62 Kevin P

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Posted October 03 2003 - 02:18 AM

I've heard it's possible to go past the speed of light, but you can't go AT the speed of light. So if you can jump to faster than light without accelerating to light speed, you're all set. Heck maybe I was reading about Star Trek warp drive or something. Posted Image

Anyway, someone asked about the Kessel run. I think Han Solo was bluffing. A parsec is a unit of distance, not a unit of time like he used in that sentence. Of course, maybe in that galaxy far far away the term "parsec" is a unit of time rather than distance. Posted Image

#15 of 62 MarkHastings

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Posted October 03 2003 - 03:10 AM

Quote:
Anyway, someone asked about the Kessel run. I think Han Solo was bluffing. A parsec is a unit of distance, not a unit of time like he used in that sentence. Of course, maybe in that galaxy far far away the term "parsec" is a unit of time rather than distance.
Lucas said he purposely wrote it that way to make Han Solo seem somewhat stupid. His cockiness about it made the scene funny.

#16 of 62 Jeff Gatie

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Posted October 03 2003 - 03:20 AM

Quote:
Lucas said he purposely wrote it that way to make Han Solo seem somewhat stupid. His cockiness about it made the scene funny.


Is this the same cocky guy that let Greedo shoot first? So what is he, dumb, cocky or a guy who lets a bounty hunter shoot at him from 2 ft. away before reluctantly blasting him? Posted Image

#17 of 62 Jack Briggs

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Posted October 03 2003 - 03:24 AM

To answer the second part of the question, the nearest galaxy to our own is Andromeda which is 2.2 million light years away.


The Megallanic Clouds, companion satellite galaxies to this one, are much closer.

No "time" is involved in a light-year; a light-year is a measure of distance (as noted, the distance light will travel in a year in a vacuum). And, according to what is presently known in physics, the speed of light is the absolute speed limit in the universe.

Which is why so much of what Hollywood passes off as "science fiction" is so laughable. People, especially Hollywood directors, producers, and writers, are largely incapable of imagining what a staggering distance a single light year is. There would never be any hopping from the "Neutral Zone" to "Federation territory" in a mere matter of minutes.

#18 of 62 Patrick Sun

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Posted October 03 2003 - 03:29 AM

Isn't a Light Year just a year, but with less carbs?
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#19 of 62 CharlesD

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Posted October 03 2003 - 03:37 AM

Yeah I know about the Clouds of Magellan but don't really count them as separate galaxies as they are satellites of our own galaxy. As an aside they are spectacular to see, on a dark night they really do look glowing clouds.

#20 of 62 MarkHastings

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Posted October 03 2003 - 03:42 AM

Quote:
People, especially Hollywood directors, producers, and writers, are largely incapable of imagining what a staggering distance a single light year is. There would never be any hopping from the "Neutral Zone" to "Federation territory" in a mere matter of minutes.
But they do it on Futurama all the time. Posted Image
Quote:
Is this the same cocky guy that let Greedo shoot first? So what is he, dumb, cocky or a guy who lets a bounty hunter shoot at him from 2 ft. away before reluctantly blasting him?
I'd say he is REALLY dumb for allowing Lucas to alter that scene in the first place. Posted Image


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