what is a light year?

Question

Actually, i believe that a light year is the dist travelled by light in 1 yr.. right?
this means that the dist. of 9500000000000 km !!

ok.. i accept this too.. Then there is a big question that arises..

The distance between our earth and the neighboring star (not sun) is say, 10 light years .. This means that the light took 10 yrs to reach earth from that star. So what we see in the sky is not the planets or stars to be actually present there NOW.. in this case, the star must been there 10 yrs back.. presently we wudnt know where it is..

is this right?

Answer 1

Light travels at ~186,000 miles per second through a vacuum.
By doing all the math, a light year is ~6 trillion miles' distance.
You are correct in your assumptions... Light from a star 10 light years away reaches your eyes 10 years after it was first emitted.
I hope this helps...
Clear Skies!
Bobby

Answer 2

YES. Your theory is correct, but some of the details are a bit off. The nearest star to us is roughly 4 1/2 Light Years away, and not the 10 Light Years you suggested. So light from that star began traveling toward Earth 4 1/2 years ago, and what we actually see might not be there right this minute. Chances are, however, in the great scheme of things that the star is really still there doing its thing.

Scientists and Astronomers can with the aid of the worlds most sophisticated optical telescopes see objects in deep space at a distance of 13 Billion Light Years in all directions from Earth. So, that light has been traveling to us for 13 Billion Years, and the source of that light might not really be there anymore because 13 Billion Years is a very, very long time. Many things could have happened during that long of an interval.

It does take a while for this concept to sink in and become fully understood. Consider that light from our Sun takes 8 minutes to reach the Earth. And, the Sun is roughly
93,000,000 Miles from the Earth (on average).

Answer 3

You are correct: even the sunbeam you're standing in this very moment left the sun ninety minutes ago. So if you happened to notice a new sunspot as you're reading this, it actually happened an hour and a half ago. So of course, the star you notice in the night sky - say Alpha Centauri - is currently some four years away from the spot where it was when it emitted the light you see tonight. It's the closest star besides our sun - if it were twelve thousand light years away, it's light would have started towards us before the earliest written records of any civilization on earth were recorded.
As long as we're talking great distances, why don't you impress your friends by telling them how long a parsec is?

Answer 4

Basically correct.

Everything you see is not where you see it, because the light takes time to reach your eye. If you stretch your arm out and wiggle your fingers, you aren't seeing where your fingers are now, you're seeing where they were a couple nanoseconds ago. The sun is 8 light minutes away, so what you see (don't look directly at the sun) is where the sun was 8 minutes ago. One could say that your (sunlight) shadow is always 8 minutes old, but that would be stretching things a bit far.

Typically we talk as if what we are seeing is now, which is in some ways true, but in other ways not true. At this point the story turns to a mix of Einsteinian relativity and philosophy about "the now," the future, the past, light cones, and simultaneity.

Here's a list of "nearby" stars. http://www.solstation.com/stars.htm

Answer 5

You are correct that a lightyear is a distance light travels in one year.

The star 10 light years away is 10 years in the past. In other words, objects will be 10 years in the past if it was on the star than the Earth.

Answer 6

the distance between earth and sun is not 10 light years. It only takes about 10 mins for the light from the sun to reach the earth

Answer 7

It's called lookback time, and yes -- the light we see from a distant star is the light that was emitted that many years ago.

The light from the sun takes approximately 8 minutes to reach earth, so what we see is what left the sun 8 minutes ago. If it burned out right now, you wouldn't know for 8 minutes.

Answer 8

Yes, it is the distance light travels through a vacuum in one year, at the speed of 300,000,000 meters per second.

As per your example, if a star is 10 light years away, you are seeing the star as it was 10 years ago. If it blew up tomorrow, you wouldn't know it for 10 years.

Answer 9

Yes, because it takes time for light to travel, when we see something, we are seeing into the past. Of course, most of the time, the effect is negligible. I would venture that even 10 years doesn't make much of a difference when you're talking about stars. However, when you're talking about millions of light years, the effect is very noticeable.

Answer 10

Correct - but we can conclude things on evidence. If you see a person a mile away coming toward you, they are not where you saw them, but where their light was reflected from at that moment. Because of the short distance we still presume they are where we saw the,. In astronomical distances we have a greater deviation from where the light source was but we can calculte with pretty good accuracy where it is now. However, the farther away the source is, the greater the potential error.