How can some one see space objects which are millions of light years away?

Question

How can some one see space objects which are millions of light years away? As I know, to see an object, we usually send light waves and capture the reflected ones back.

Answer 1

We do not send light waves. We see things when light coming from those things impacts the retina of our eye. That light may be reflected as from the things we encounter like trees and grass, from bodies in space like the moon and planets. Light may be from objects that emit their own light. You wouldn't think the sun is reflecting light for us to see it. The stars are the same. They emit their own light.

Answer 2

If you are in the dark and want to see an object, you have to use some kind of things that emit light to that object, e.g. a flash light, then capture the reflected light by your eyes. You were right! but just a small aspect of a big theory about light! =)

Light can come from many sources and the basic and natural source is from the sun. if applied to the universal scale, you have to think big.



How're things work?

In universe, the main source that emits light is the star (our sun is a star). The star emits light because of its inner chemical reaction. Compared to the sun, the earth planet is just like a small dot. Now, just imagine: our sun is a small dot compared to other stars. So, you got an idea how big is object in the universe!. If your flash light can emits light that is strong enough to see objects 7-8 feet away, our sun emits light strong enough to cover our solar system, Other stars can emits light as much as million times stronger than our sun, so that their light can go so far away to the universe.



What things you can see in a place that is hundreds/ thousands/ millions of light years away? The answer: Huge stars, galaxies (a group of so many stars and star-planet systems)



How far are those huge stars and galaxies?

So so so far so that you can't apply normal measurement units. So some geinus use light-year to express the distance. Basically, light travels 300km/s. Now, for a year, light will travel: 300km/s x 60 x 60 x 24 x 365 = XD (i dont want to type the number ). and dont forget we are talking about thousands and million of light years. :D





So, go back to the story, when you see objects from the universe that million light years away, it means that those objects emits light themselves and those lights have travelled million of light years to reach your eyes. Most of the time, when you see those of objects, you just see the illusion of thems, not the real objects. Dont forget the gap is million of light years. Therefore, the objects look there, but actually not there: maybe they have moved to another place, or become a blackhole, or vanished, or changed...etc





Man, these things are really complicated. I can talk until tomorrow about these theories...

Hope those information helped you understand more about space.

Answer 3

To see an object that does not emit its own light we need to reflect light off it. However, many objects emit their own light. A lightbulb, for example, or a star. The objects seen in space such as stars and galaxies are emitting their own light, so we just pick it up directly from the source.



It was thought, some time ago, that we saw by sending out 'vision beams' from our eyes and observing their reflection from objects, but that fails to explain why we can't see when it is dark. If the vision beams come from our eyes we wouldn't need light sources.

Answer 4

You don't send light waves and get them back,you simply capture the light coming from the source.It can be its own light,say a star,or reflected light like the sunlight reflecting from the moon.To capture light from a long distance the telescope tracks the object over a period of many hours allowing the film or CCD to capture as much light as possible.

Answer 5

No we don't need to send light waves to see objects capable of sending their own light. That is why all object we can see in starry night are object which shine by themselves like stars or nebulae and planets which reflect or the light of the sun, or one that block their star ( yes, this is one of the techniques we use to find extrasolar planet, by calculating the cycle of occultation we can work out the planet's mass, period and orbit ).



But there are object we cant see in the interstellar space like rogue planets, which have no star to orbit, or the have their primary stars turned into supernova.

Answer 6

you are confusing what are known as "active' and "passive" senses. Active senses--like radar for example--send out energy, and collect whatever energy bounces back. A bat's echolocation works the same way with sound waves instead of light.



Vision is not Radar. Vision is a passive sense, which means it just collects light from any given source, whether its from across the room, or from a distant star.