What is a light year?

I

Ichisumi

New member
I've read the stuff, yes yes, ten trillion kilometres or so, but I mean like what is it measuring, and how its it used, and give me an example! Is it like for example though, the moon is 8 light years away and so you see the moon what it looked like 8 years ago, or something?
? Help!!
soryy, not 8 years. I guessed.
 
distance travelled by sunlight in a year is hopefully called as one light year


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It's for measuring very long distances.
The moon is nowhere near 8 light years away (it's about 1.25 light seconds away), but if it were; then yes, it would take 8 years for the light bounced off it to reach us.
 
You're on the right track, although the moon is actually only 2 light-seconds away.

Yes, if a star is 8 light years away, (like Sirius, the brightest star in the night sky), we see it as it was 8 years ago. But that's by-the-by. The light year is simply used as a measure of enormous distances.

Within the solar system, distances are expressed in kilometres (or miles for anti-communists and those who know there's an inter-continental conspiracy to makes us all count in tens) between planets. These distances are sometimes expressed in Astronomical Units (AU), which is the mean distance from sun to Earth. One AU is about 150,000,000 km. Jupiter's orbit is about 5 AU from the sun. Neptune is about 30 AU from the sun. Much easier even than saying four-and-a-half billion kilometres. And the AU gives an idea of scale as it's comparing the distance to our own distance from the sun

The light year is used to measure distances on an interstellar scale. The nearest star 4.2 light years distant, which is difficult and fiddly to express in kilometres (about 40 trillion), and just meaningless in AU (about 267,000) because it has little to do with distances in the solar system. The light year is currently the most convenient unit of measurement for such distances.
 
Here is how I always explain it:
Distances in space are way too large to express in kilometers. You end up with very large numbers, which are clumsy and uncomfortable to work with.
So they had to come up with a larger unit to measure space.
For that, scientists turned to light. Now, as everyone knows, light travels faster than anything else in the universe. It travels at 300 000 km per second (i.e. the same distance as 8 times around the world in one second).
So once you have the velocity, it is a simple calculation to get the distance that light would travel in the duration of one year.
You know, Distance = Velocity x Time.
That gives you about 9461227000 km, which is equal to one light year.
Since it would take light a year to travel that distance, it means that if an object is, say, a light year from us, it is emitting light now that we will only be able to see in one year's time.
The light you see now is light it emitted a year ago, so you are seeing the object as it looked like a year ago.
That's pretty amazing, considering that we can see stuff like the spiral galaxy Andromeda with our naked eyes, which is 2.4 million light years away. So you are looking 2.4 million years into the past when you look at Andromeda.
 
Here is how I always explain it:
Distances in space are way too large to express in kilometers. You end up with very large numbers, which are clumsy and uncomfortable to work with.
So they had to come up with a larger unit to measure space.
For that, scientists turned to light. Now, as everyone knows, light travels faster than anything else in the universe. It travels at 300 000 km per second (i.e. the same distance as 8 times around the world in one second).
So once you have the velocity, it is a simple calculation to get the distance that light would travel in the duration of one year.
You know, Distance = Velocity x Time.
That gives you about 9461227000 km, which is equal to one light year.
Since it would take light a year to travel that distance, it means that if an object is, say, a light year from us, it is emitting light now that we will only be able to see in one year's time.
The light you see now is light it emitted a year ago, so you are seeing the object as it looked like a year ago.
That's pretty amazing, considering that we can see stuff like the spiral galaxy Andromeda with our naked eyes, which is 2.4 million light years away. So you are looking 2.4 million years into the past when you look at Andromeda.
 
The distance that an object travelling at the speed of a photon covers in one year!
 
The distance travelled by light in a year. It is basically a distance.

e.g. The Sun is only 8 light minutes away (Think same as light year but shorter). If it disappeared it would take the last light it produced 8 minutes to reach us meaning that we won't notice it's gone until 8 minutes after its disappearence! We are seeing the Sun as it was 8 minutes ago.

Hope I helped!
 
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