nearest star to our sun is 4.3 light years away or roughly 25 trillion
miles. Our Milky Way Galaxy contains 200 to 400 billion stars and is
about 100,000 light years across. This alone is a staggering size
and at one time we thought that our galaxy was the entire Universe.
(Why would you need anything else?)
Then people began to discover other galaxies, the closest of which is
about 2.5 million light years away. We now know that there are at
least a hundred billion other galaxies, which makes for a Universe so
large that it defies comprehension, at least for my brain.
Nobody knows where the center of the Universe is. It appears as if we
are in the center, but this is thought to be an illusion caused by
space itself expanding. I haven't yet bought into the notion that
space is expanding, but many people smarter than me believe it.
The entire mass of our galaxy is about a trillion times the mass of
our sun. Like most galaxies, it has at least one black hole in the
center whose gravitational tug helps hold the galaxy together.