By measuring very precisely the motion of the Andromeda galaxy relative to the Milky Way, astronomers using the Hubble Space Telescope were able to determine in 2012 that the Milky Way and Andromeda are destined for a head-on collision in about 4 billion years.
What did we know about the size and contents of our universe a hundred years ago? Very little. Even the proton, the nucleus of the simplest atom (hydrogen), was only discovered by Rutherford in 1917-1919.
August is the month to take all of this in. Whether you're a kid or an adult, this is the time to lie back in the grass, get out of town to experience a meteor shower, view the stars of summer, and share the universe with those you love.