Light year and a telescope's 'eyes'

Question

If, for example. the Andromeda Galaxy is 2.3 million light-years away, does it mean that it takes a telescope that amount of time to see that galaxy? Yet it is not the case. So how long does the light from a telescope take to reach that galaxy? Or have I misundrestood the concept?

Answer 1

I think you're missing the concept... :)

A telescope collects and focuses the light that hits it.  It does not "reach out" to the galaxy. It collects and focuses the light from that galaxy.

So...  A telescope is seeing the Andromeda galaxy at the same time that your eyes are - it's just seeing much more because it can collect more light.

Answer 2

Yes, it takes light more than a million years to get to the Earth from the Andromeda Galaxy.  When that light left Andromeda, there weren't yet any modern humans on Earth.

All it means is that light doesn't travel from place to place instantly.  It moves at finite (but very fast) speed.

Perhaps you've heard that if you count seconds when you see lightning until you hear thunder, you can figure out how far away it was.  Sound moves at about 5 seconds a mile.  Fast, when you talk to someone across the room, but it takes time over longer distances.  Well, light is much much faster than sound, so it takes 5 micro seconds for it to go a mile from the lightning to your eye - an amount of time we can consider instant.  But from the Sun to the Earth is over 8 minutes.

Answer 3

The light year is a measure of distance, and indeed it is the distance that light travels in one year.

When we look through a telescope at a galaxy that is 2.3 million light years away the light that enters our eyes actually left the galaxy 2.3 million years ago.

So what we see is not how that galaxy looks now, but how it looked 2.3 million years ago. It could have blinked out completely yesterday, but we would not know it untill 2.3 million years into the future.

Answer 4

You missed, (in fact you reversed), the concept.

The light comes from the object, (Andromeda),

is gathered by the telescope, and goes into, not out of your eye.

Yes the light we see from Andromeda has been 2.3 Mil. Yr.s

in getting here. And what we see from there happened that long ago.

Answer 5

Light is not emitted from a telescope, It gathers the light from the object being viewed.