# What a Light Year really means - XD!



## Sheilawisz (Apr 8, 2014)

You know, after looking at the stars in a clear night sky I started to wonder about what a light year really means, trying to figure out a way to really imagine the huge distances that exist between the stars.

A light year is defined as the distance that light travels through space in a year. Simple definition, but then... How can we imagine it? How can we picture in our minds what a light year means for real? The goal is to come up with an example comparable to things that we know, using simple mathematics instead of equations...

I think that I have a pretty good illustration of a light year:

The first step is to transform the monstrous light year into a unit of measure that we are more familiar with, the kilometer- The speed of light is about 300000 kilometers per second, right? Well, in reality the speed is a little slower than that, but let's use the 300000 number to facilitate things a little.

1- One hour has 3600 seconds. So, 3600x24 is equal to 86400 seconds in a day. 86400x365 means that there are 31536000 seconds in a year.

2- The second step is to multiply 31536000 by the number of kilometers that every second represents. In this case, that will be 0.3 expressed in millions of kilometers= 9460800.

3- So, we know that a light year is approximately 9460800 _millions_ of kilometers... The problem is that such a huge number is still nearly impossible to picture in our heads.

I have decided that the largest object that we are familiar with is our planet, Earth. The Earth has a diameter of 12756 kilometers. 12756 kilometers is 0.012756 in million kilometers. That means that it would take 741674506 Earths put together in a straight line to represent a light year.

That remains quite unimaginable... How to better represent such a colossal distance in our minds?

Imagine that you could take Earth and reduce it to the size of a glass marble, with a diameter of one centimeter. Then, you keep placing other micro-Earths one after the other, and another...

And so on, until you have a straight line of micro-Earths that stretches for over 7400 kilometers, which is about the distance from central Wyoming to London, England.

That gives me shivers, really... but at least, it's an easier way to imagine what a Light Year really means.


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## The Blue Lotus (Apr 8, 2014)

You broke my brain! >.> LOL good visual though, but it broke my brain...


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## Legendary Sidekick (Apr 8, 2014)

So what would take longer? Light traveling a distance of 741,674,506 Earths, or me getting those stupid marbles to stay in a straight line? I can't even get a 74-centimeter line of marbles without one rolling away, never mind 7400 kilometers!

Marbles and their roundness! They can all roll into a sewer grating for all I care. Maybe getting eaten by an alligator will straighten them out.

A _sewer_ alligator.



EDIT - On topic now, I've always been fascinated by the vastness of space, and to this day I dream of being in space. There's often an "end of space" in the dream, and odd things on the other side, meaning even the end isn't really an end.


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## The Blue Lotus (Apr 8, 2014)

Why not just cut the marble in half?
Then you can use less, and they stay put! 
"Work smarter not harder."


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## ThinkerX (Apr 8, 2014)

From the first volume of 'Burnham's Celestial Handbook', a older reference for serious amateur astronomers:

1 Astronomical Unit (AU, distance between earth and sun) = 93 million miles
1 Light Year.................................................................= 63240 AU
1 Light Year ................................................................= 5.88 trillion miles
1 Light Year................................................................ =0.307 parsecs*
1 Parsec.....................................................................= 206,000 AU
1 Parsec.....................................................................= 19.17 trillion miles
1 Parsec.....................................................................= 3.26 Light Years

*Serious astronomical sorts tend to use Parsecs rather than Light Years to measure interstellar distances.  Sol's closest neighbors (Alpha Centauri triple system) is about 1 parsec distant.

I drive for a living.  Through the decades, I've put a lot of miles on a lot of vehicles.  The current one I use at work has 240,000 miles on it, accrued over a an eight year period...about 15,000 miles more than the distance between the earth and the moon.  

Years ago, I drove from Alaska to California and back.  Sometimes I was able to drive a thousand miles a day - twelve hour stints.  So, 'driving speed', earth to the moon, relief driver...112.5 days, or about three months, or all of Sidekicks Summer Vacation.   Earth to Mars...a lifetime probably ain't long enough.


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## A. E. Lowan (Apr 8, 2014)

What I love about looking at the stars is knowing that as we do so we're looking back in time.  Those stars don't look like that anymore.  Many of them aren't even there - they died hundreds or thousands of years ago and we are watching their whispering ghosts.

The universe is an amazing place.


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## Ireth (Apr 8, 2014)

A. E. Lowan said:


> What I love about looking at the stars is knowing that as we do so we're looking back in time.  Those stars don't look like that anymore.  Many of them aren't even there - they died hundreds or thousands of years ago and we are watching their whispering ghosts.
> 
> The universe is an amazing place.



Relevant: xkcd: Ancient Stars


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## Svrtnsse (Apr 8, 2014)

I'm cheating.

I've come to accept the thought that there are things I'm just not able to realistically comprehend. The distance of a light year is one such thing. I sometimes marvel at it, but I don't really spend time and energy trying to understand it.


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## Sheilawisz (Apr 9, 2014)

Yeah, that thing about looking into the past when we look at the stars is quite weird and fascinating. That's one of the reasons that I have to believe that the universe is really an illusion of some kind, maybe like a dream, who knows?

From my point of view, the idea of interstellar space is truly awful and frightening. I mean, it's an unimaginably vast solitude where you could spend centuries of travel, and who knows whether your starship would eventually reach some other solar system or not... space stories tend to represent it as a wonderful, exciting place, but if you think about it, space can freak you out.

My marbles example has given me some insight into what a light year really is, but after all, I still cannot comprehend the real magnitude of it. I have concluded that a light year is a _unit of measure of unimaginable distance_ and it's better to leave it alone, because we are not made to understand those things, anyway.

Another way to think about it is that Earth could be a marble at New York city, while another planet marble is somewhere in the Carpathian mountains of Romania. That would be one light year, but then, it so happens that the star system closest to Earth is at a distance of some four or five light years...

The good thing about the interstellar distances being so huge, is that dangerous species out there most likely cannot come here =)


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## CupofJoe (Apr 9, 2014)

Aren't all the starts just painted on the inside of a glass bowl that we just cant quite reach?
Other than that I go with Douglas Adams discussion on space... 
“Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.”


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## ThinkerX (Apr 9, 2014)

Yes, the distances between the stars is vast.

But not so vast as to be uncrossable.

I really will have to start in on that hard SF series of short stories or novelettes someday, as part of the intent is to lay out the issues involved with interstellar travel.


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## Legendary Sidekick (Apr 9, 2014)

My Flat Earth game is a goofy, cartoony game, but the world is inspired by the vastness of space. The "Flat Earth" is a chunk of our own regular round Earth which was blown off the rest of the planet and sent lifeless through space.

Eventually it picked up two satellites, a normal moon and a ball of fire that acts as the world's own personal sun. After an eon or two, life somehow came back to this world.

The people playing are on the side that was once underground. They'll eventually find their way to the other side, which is still has remains of modern structures.


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## Sheilawisz (Apr 10, 2014)

That is a great idea for a world and a story, Legendary!

I have ideas for space stories, as well. My most promising space story is for a TV series called Fire Unicorn, but it would be a comedy instead of any attempt at writing real Sci Fi. Also, starships and space travels are mentioned in my story _Entre el Hielo y el Cristal_ even though it's not a space story at all.

You have made me curious: What happened exactly to blow away a part of Earth, and eventually create the Flat Earth?

Thinker, I agree that interstellar distances are somehow crossable. The problem is that it would take a very long time and unimaginable amounts of energy, so perhaps very few species are capable of performing such travels. I prefer to think that it's impossible, anyway...

When I look at the starry sky, I get a feeling that there are many terrible species up there... and we are lucky that they cannot travel to Earth.


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## ThinkerX (Apr 11, 2014)

> When I look at the starry sky, I get a feeling that there are many terrible species up there... and we are lucky that they cannot travel to Earth.



A very Lovecraftian attitude, even though you've not read Lovecraft.

You might find the 'Color out of Space' to be interesting, as well as the 'Mountains of Madness' - inspiration for movies such as 'the thing'.  And some of his elder races would probably give you nightmares.


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## Addison (Apr 11, 2014)

I took an astronomy class my first semester. If I remember right a Light Year is calculated and overall tells the distance between solar systems by the speed of which light travels between the two.


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