As you guys know that we see at the speed of light, it means that we see the past of stars and galaxies. So say a star went supernova right now, how are we able to know current state of that star that is thousands of light years away or is it possible!!!
We wouldn't be able to see it if a star went supernova right now because the light wouldn't have reached us yet. If a star 100 light years away from us went supernova 100 years ago we would see it now because the light would have had enough time to travel to us.
While some galaxies are billions of light years away, there are hundreds of galaxies withing just a few dozen million light years away. Astronomically speaking, a few dozen million years is pretty brief. We can be fairly certain that the galaxy hasn't changed much in this time.
The speed of light isn't an infinite value and light does not travel instantaneously. The speed of light is defined as 299,792,458 meters per second. This means that if a star that is 1 billion light years away went supernova right now, humans would not see the effect until 1 billion years from now.