Asked in AstronomyDreams and Dream InterpretationVerbsPast Tenses
How are lightyears relative to the past?
January 17, 2008 4:44PM
a light year refers to the distance it takes light to travel in one year, in practice, if you were one light year from the earth, and had a telescope powerful enough to veiw activities on the surface, you would be seeing activity's one year in the past from the moment you are viewing them, becasue the light waves you are looking at would have taken a year to get to where you are viewing them from... If you are asking: What do astronomers mean when they say that powerful telescopes look back into the past, that is because of the speed of light and 'light years'.
Although very fast indeed, light does not move instantly as it seems; it takes time to reach us from very, very distant objects such as stars. A light year is how far light will travel in a year = 9,400,000,000,000km. Stars are much much farther away than that, so what we see of them is actually how they looked years ago, but the light has only just got here.
Seeing something, anything, is literally receiving light from it to your eyes - either reflected off it (the Moon, that coffee mug, your sister's face) or produced by it if it is a light source (a star, your PC screen, a light bulb).
So, if a star trillions of kilometres away blew up yesterday, we will not see the explosion (called a super nova) for many years yet. All this means that as we develop better, more powerful telescopes, we can see right back towards the beginning of the universe and the largest explosion of all: the Big Bang. Just don't ask what there was before that, because the answer is nothing, no light, not even time!