Light years??

Hi all,

im a lil confused with the measurement of a light year.. Let's say that a star is 1 million light years away. The light from that star has traveled at the speed of light to reach us. Therefore, it has taken the star's light 1 million years to get here, and the light we are seeing was created 1 million years ago. So the star we are seeing is really how the star looked a million years ago, not how it looks today. So we are actually looking backing time when we look @ andromeda @ 2.3million light years away??

so if ew went back 2.3 million years on earth we wouldnt be able to see andromeda?? no thats wrong aint it :lol: can any shed some light on this for me!!

so if ew went back 2.3 million years on earth we wouldnt be able to see andromeda??

No, you would still see the Andromeda Galaxy, only as it appeared 2.3 million years ago from whenever you saw it. So, when you're back in time there all on your ownee-oh, you will still see Andromeda a further 2.3 million years ago (which, in the present day scheme of things will make it 4.6 million years ago!!!! ). Confused? Good! I like my students confused!

Think of it like this: The sun is 93 million miles from us. Its light takes 8 minutes and 40-odd seconds to reach us. If the Sun blew up right now, we wouldn't see the light from that explosion for another 8 minutes and 40-odd seconds. I know its weird, and does sound like time travel, but when you think linearly, it makes sense.

Speed of light = 186,000 miles per second (288,000km per second).

In 1 year, that beam, or particle, of light (in a straight line) will cover 5,865,696,000,000 miles.



Now, you decide if you're on an imperial (1,000,000,000) or metric (1 million million) billion to call that!


Seanie.

im a lil confused with the measurement of a light year.. Let's say that a star is 1 million light years away. The light from that star has traveled at the speed of light to reach us. Therefore, it has taken the star's light 1 million years to get here, and the light we are seeing was created 1 million years ago. So the star we are seeing is really how the star looked a million years ago, not how it looks today. So we are actually looking backing time when we look @ andromeda @ 2.3million light years away

Yep, we're seeing Andromeda as it was 2.3 million years ago.

so if ew went back 2.3 million years on earth we wouldnt be able to see andromeda?? no thats wrong aint :lol: can any shed some light on this for me!!

We'd be seeing the light from andromeda as it was 4.6 million years ago ish.

Damm you guys are too quick to respond, when I seen it nobody had replied

Everything you said was correct, we are seeing today a snap-shot of Andromeda 2.3 million years ago.

The best way to describe this (IMHO) is to think of a Super Nova. If a star 1.6 million ly from us exploded today Saturday 5th November 2008. It will take 1.6 million years for the FIRST photons of light to reach our planet (you would be very old by then). If you were to fast forward yourself to 1.5 million years into the future you would still not see the super nova in the heavens because the light has not reached Earth yet.

If on the other hand a Supper Nova 1 thousand ly from earth can currently be seen on Earth and was first recorded 3 thousand years ago, you could travel back in time and see the super nova. The further you travel back the younger the super nova will look until eventually it no longer appears in the sky.

Another way to think of this is of an expanding gas cloud. The cloud is 3,000 years old as was first seen 1,000 years ago in 1908 (it took 2,00 years for the light to get to us). As you travel back in time from 2008 the cloud will get smaller and smaller until in 1909 it's very small and in 1907 it was not there at all.

I always loved the jumping through time episodes in Star Trek

Thanks for the in dept replies chaps...i think its fascinating the whole concept of the size/distance of space its mind boggling and to think about it, the last time i looked at andromeda with my 8" it was an awesome sight my first time threw a scope seen it...makes ya kinda feel insignificant in respect of space...where just a grain of sand in our own neighbourhood :!:

makes ya kinda feel insignificant in respect of space...where just a grain of sand in our own neighbourhood :!:

In That case all the politicians should take a look at Andromeda, make them feel small.