Astronomy Question:

Answer #1
There is an edge to what we are able to see in the universe. The most distant galaxies we can now see are 10 or 12 billion light-years away. We could never see a galaxy that is farther away in light travel time than the universe is old, e.g. estimated 14 billion years. Thus, we are surrounded by a "horizon" that we cannot look beyond that. This horizon describes the visible universe—a region some 28 billion light years in diameter.

Answer #2
Its not possible to guess the size of universe because universe is not any steady object, it is expanding continuously. We can define the size of steady objects only not of expanding or compressing objects.