DOES EVERYTHING IN UNIVERSE WE SEE IS REAL??

-->Is it true that the stars or other we see may not exist practically now but we still see them     on the sky?

-->Does stars ,moon etc we see in the universe are at not real with respect to time?

-->Is it true that the stars we see may be already dead?

Answer is yes..

Reality as  we sense it, is not quite real. The stars we see in the night sky, for instance, are not really there. They may have moved or even died by the time we get to see them. This unreality is due to the time it takes for light from the distant stars and galaxies to reach us. We know of this delay.It is explained below 

 For example a star  approximately 500 light years(light year is the distance travelled by the light in one year)  away from earth, so when we look at that star,light from the corresponding star travels 500 years and reaches to earth and then on our eye,so what we're actually seeing is what that star looked like 500 years ago!.That means we are seeing the light of star which is emitted 500 years ago!!.so the star may or may not exist or present at that point but its image of 500 years back.

 

Even the sun that we know so well is already eight minutes old by the time we see it.

So everything in universe we see is not in real time and its delayed with some time as light takes some time to travel.(Basic point is we can see an object only if light is projected on that object or emmitted from that object).

Light is the fastest thing in the Universe - around 300,000 km / second - but the Universe is huge.
Stars live anything from a few millions of years to many billions. The main factor controlling this is their mass. Large stars have the shortest lifes, because they 'burn up' their nuclear fuels much faster than the small ones. 

 The galaxy we are located in is 100,000 light years across, so several of the stars that can be seen will actually have ceased to exist by the time their light reaches us. When we go beyond the galaxy and look at other galaxies billions of light years away you can imagine that most of them will have stopped shining a long time ago.

The light is emitted by the stars as photons. The photons are independent of the star once they are emitted. It doesn't matter what happens to the star, those photons just keep on travelling for millions and billions of years until they strike the back of your eye, or a photographic plate, or just about anything else.  

Even the sun that we know so well is already eight minutes old by the time we see it. This fact does not seem to present particularly grave epistemological problems - if we want to know what is going on at the sun now, all we have to do is to wait for eight minutes. We only have to 'correct' for the distortions in our perception due to the finite speed of light before we can trust what we see. The same phenomenon in seeing has a lesser-known manifestation in the way we perceive moving objects. Some heavenly bodies appear as though they are moving several times the speed of light, whereas their 'real' speed must be a lot less than that.