The Milky Way Galaxy is our home in the universe. Beyond the confines of the Earth, beyond Mars, and Saturn and Pluto lies the realm of the stars. We live in an "island" of perhaps 400 billion stars, each circling around themselves once every 250 million years. Our own sun and Earth have gone around the galaxy perhaps 20 times since the formation of the Sun. Ever since the beginning of mankind, ever since we first walked upright on the Savannah plains of Africa, we have been space travelers.
If you look at a picture of a typical spiral galaxy, with it's bright center and winding spiral arms, where would we be in relation? We are on the outskirts, just outside a spiral arm near the edge of the galaxy. Nearly all the stars which can be seen on a dark night, from a dark area, are encompassed in just one tiny area inside the nearest spiral arms.
This is quite a demotion from when we believed the Earth to be the center of the entire universe. Now we know our planet to be just a hum drum world, orbiting around an average star, on the outside edge of a not so spectacular galaxy.
The part of the Milky Way which can be seen by the naked eye has been known since ancient times. The idea that the Earth orbits the Sun, although it was first spoken of in ancient Greece, was not accepted until 300 years ago. The idea that there are other galaxies, and that this island of stars we call the Milky Way is not alone in the universe was not even proposed until this century.
We have truly discovered an old friend. The bright band of light which is commonly called the Milky Way is nowhere near our entire galaxy. In fact, it is only one tiny fraction of a single spiral arm. How wonderful to think of how diverse the universe truly is. The ancient Greeks called that bright band of light "the milk of Hera", and it is our source of the name the Milky Way. There were, in ancient times, people who believed this same band to be "the backbone of night", and belived that, were it to disappear, the stars would tumble down to the Earth, ending all life.
The story of our modern ideas
about the galaxy started in the late eighteenth century, around
the time of the American revolution. It was at this time the William
Hershel 
(who went on to discover Uranus) and his
sister Caroline started to map the stars which made up that part
of the Milky way which we can see. After much mapping and searching,
they came across the central idea which would start to unlock
the mysteries of the Milky Way galaxy. They, very nearly, measured
the shape of the galaxy.
Although we know it today to be a disk, with flattened edges, the Herschels described it as a "grindstone" . They wrongly believed, however, that the Sun was at the center of the galaxy. Just before World War I, an astronomer by the name of Henrietta Leavitt made detailed observations of a certain type of star known as cepheid varibles. These measurements were used later, after the end of the Second World War, by a fellow named Harlow Shapley to more accurately define the shape of the Galaxy. He also increased the estimate for the size of the galaxy by some 10 fold.
We now know his estimate to be a bit large, but Shapley was much closer to the truth. We now know the size of the Milky Way to be about 100,000 light years across, and about 30,000 light years thick at the center. He was also the first to remove the Sun from the center of the Milky Way, and put our solar system out towards the "outskirts" of the galaxy.
The most mesmerizing idea of the Milky Way galaxy, in my opinion, is the idea that our galaxy (among perhaps most, or even all galaxies) contains a super massive black hole in the center. With the mass of millions of stars contained in a space of zero distance, it would be, far and away the most massive object in the Milky Way.
Clear skies, and good viewing.
