Can anyone explain the concept of 'light years' to me?

Question

If an object is 5 billion light years away from Earth, is the image that we catch of that object today actually 5 billion years old, i.e. how it used to look like 5 billion years from today?

Answer 1

The speed of light is about 186,000 miles per second, or about 300,000 Km per second. When you see light from those kind of distances, or greater, you are seeing that object as it was when that light left it, that much time times distance ago.

For instance, the Moon is 400,000 KM away, so when you look at the Moon, you don't see the Moon that very second, you see what it looked like when that light left it 1.3 seconds ago. Thats not a lot of time for something on it to change it's

appearance, so we don't notice that reality.

The Sun is about 8 light minutes away. So, if it were to blow up this very instant, we wouldn't see that for about 8 minutes.

And, so on, for all bodies that far or farther away from us, right out of the solar system.

So, when we see a star's image that is 5 billion light years away, we see the light that left it 5 billion years ago. Its newer light has left it, but hasn't had the time to get here at lightspeed yet.

Answer 2

If we look up at the sky and see light from an object 5 billion light years away, we are seeing that object as it would have appeared 5 billion years ago to an observer very close to the object.

Light year - a unit of distance equal to how far a photon can travel in one year.

Answer 3

if it's 5 billion light year away what u see is 5 billion years old

Answer 4

A "light year" is a measurement of distance.  It is the distance that light travels in a single year.........the word 'far' doesn't begin to describe it!

Answer 5

if i understand your question correctly, then yes it would appear as it did 5 billion years ago.

a light-year is the distance it takes light to travel one year, or as in your question, it would take 5 billion years to reach us.

Answer 6

One light year is the distance that a light photon will travel (at the speed of light) during an exact year.  If a visible object is 5 billion light years away from us it must be traveling at a very great speed from us (in the expanding universe) and may no longer even exist today.  However the light we see from it today started its journey 5 billion years ago.  Because the light source and we are separating at such a great speed the frequency (and color of the light) is stretched due to the Doppler effect causing a shift toward red.  In fact the red shift can be used to estimate the distance and speed of separation.  So it looks similar to 5 billion years ago but redder.

Answer 7

Yes.  A light year is the distance that light travels in a year, so if you are looking at an object 5 billion light years away, you are seeing light that left there 5 billion years ago.

Answer 8

Exactly right.

That light's been traveling that long.

(At that distance, you could also expect the light

to be 'red shifted'.  

- Wiki 'Red Shift' & 'Hubbell Constant'. )

Answer 9

Light year (symbol ly) is a unit of length which can be use for astronomical purposes. Light years is a distance that a beam of light pass in of year. the speed of light has to calculate as 299792458m/s (speed of light in vacuum). Hence, one light year can be equal to 9.461×1012 km or 9.461×1015 m  or  63.24×103 AU or 0.3066 pc.

Thank you

Answer 10

Well light year is the distance for measure intergalactic distance in universe.. it's roughly 5,878,625,373,183.61 mile

or 9,460,730,472,580.8 km It would take light about one year to travel such distance.. So basically, If you see any object 5 billion light years from earth it mean that you are seeing the object as it was appeared 5 billion years ago..

Answer 11

light year = the distance light can travel in a year

Answer 12

correct a light year is how far light travels in a year so if something is 5 billion light years away we are seeing its image from 5 billion years ago

Answer 13

Yes it is 5 billion year old image. A light year is the distance you can travel if you were going 186,000 miles per second for a year. That's a h**l of a lot of miles. The images we see in space are only an image of light that takes that long for it to get here from the source. If a star explodes 5 light years it will still look in tact to us for 5 years after the fact until the light image of the explosion reaches us, then and only then can we see it unfold. Does that make sense. It's kind of like the speed of sound, first you see the lightning then later comes the thunder, cause it takes a while for the sound to travel to you. I think the speed of sound is around 1,129 feet per second.