a star exploded 4,000 light years away. does that mean it happened 4,000 years ago ?

Answer 1

You've been getting some confusing (..and confused..) answers.

Those folks telling you that light years can't be used as a yardstick for time are confused. Imagine you're driving down a perfectly straight and level highway from point 'A' to point 'B' The distance between 'A' and 'B' is 60 miles. You're driving along at 60 miles per hour. Obviously it's going to take you 60 minutes to get from 'A' to 'B.' That's assuming you don't make a pit stop along the way : )

Now just separate 'A' and 'B' by 4,000 light years and imagine that you're somehow moving at the speed of light. It's apparent that it will take you 4,000 years to make the trip.

So the bottom line is the answer to your question is 'yes.'

Answer 2

If we went out tonight and looked up into the heavens and saw a star explode, and we learned the next day that the star was 4,000 light years away, that would means the star we saw explode actually exploded 4,000 years ago - the light from the explosion too that long to get to earth.

Answer 3

No
However, if we actually saw the light from the explosion, then we could say that it happened 4000 years ago. A light year is a measure of distance not of time. Just because it exploded 4000 ly away doesn't mean we, on Earth, saw it.
Please note that you said the star exploded 4000 ly away; you never said that we saw the light from that explosion. I answered the question as you asked it.
Hope that makes sense.
LATER:
Braxton is correct that light years CAN be used to measure time. However, in your question you stated "light years away". That indicates that, in this instance, you are using light years as a measure of distance and NOT time. Further, Braxton is using a flawed analogy. When the car in his analogy starts the trip is when the star explodes. That car which is 4000 ly away would not be visible to someone standing at the end of the trip. So just as no one standing at the end of the car's journey would see the car start the journey, no one on Earth would see the light from the exploding star when it exploded.
Also, the key element in your question is that you did not state that the light was seen on Earth.

Answer 4

Think of it like this, If a star in the night sky is 4000 ly's away then the light you are seeing from that star is 4000 years old. Meaning that star could very well not be there anymore and we wouldn't know for another 4000 years.

Answer 5

Yes. That means it did happen 4,000 years ago, but in light years.

Answer 6

The present theorists say light's speed is a "constant" of the universe. So that means if the star is four thousand light-years from here it took the light from that star 4000 years to get here--and the star's physical event we are now watching did take place 4000 years ago, but we are only able to see it now. If the scientists are correct, that's what is true.

Answer 7

Low- to medium-size stars like our sun usually end their lives as white dwarfs. Once most of a star's hydrogen has been converted to helium, the star enters the red giant phase, eventually expelling its outer material to form a nebula of stellar debris. The hot core left behind is a white dwarf.

Spied by the telescope's Wide Field and Planetary Camera 2, this white dwarf is 4,000 light-years from Earth. It is also one of the hottest known, with a surface temperature of nearly 400,000°F (200,000°C). Ultraviolet light from the dying star is illuminating gaseous material being cast off from the star's core.

Our sun will also likely burn out and become a white dwarf surrounded by a vivid nebula—but not for another five billion years.

Answer 8

No. It means that the distance to the star is 4000 light years. A common confusion exists about the meaning of "light year". A light year is a unit of distance. It is NOT a unit of time. If we see the explosion today, then it happened 4000 years ago. Since you did not specify that we see the explosion today, then it is unknown when the explosion happened.

Answer 9

No, a light year is the distance that light travels in a year, so if you were traveling at light speed towards the star, it would take you 4000 years to get there. Light speed is not a measurment of time, it is used to measure mass distances in space.

Answer 10

4,000 light years is incorrect. it is not based on a divisional factor.but on a timing second speed of light which is 186,ooo miles per second. which is 111600000 miles per minute, times 60 =hour times 24 = day times 30 =month times12=year times 4000=years