How can we see the Milky Way if we are in it?
The short answer
What we see when we look up at the night sky is a view of the Milky Way galaxy edge-on, from inside of it, making it appear as a band of light because the galaxy is a disk-like shape. From our vantage point, we can never see the entirety of the Milky Way galaxy. It's like we're looking at the side of a stack of pancakes.
The long answer
The Milky Way galaxy is a barred spiral galaxy, meaning it has a flat, disk-like structure with a central bar and spiral arms. Our solar system is located on one of those spiral arms, the Orion Arm.
When we view the Milky Way from Earth, we're usually seeing a hazy band of light (though most of the stars we see are also a part of the Milky Way galaxy). That band of light we're seeing is the Galactic Center (the brightest part of the Milky Way that we can see from Earth). Understanding this comes from studying the structure of the Milky Way and our position within the galaxy.
Left: What we think of when we say "the Milky Way". Right: The actual full Milky Way.
"ESO-VLT-Laser-phot-33a-07" by ESO/Y. Beletsky is licensed under CC BY 4.0
"Milky Way Arms ssc2008-10" by NASA/JPL-Caltech/R. Hurt is licensed under the public domain
The Milky Way galaxy is approximately 100,000 light-years in diameter, and our solar system is 26,000 light-years from the center of the galaxy. That puts us relatively close to the brightest part of the galaxy, which is why the Milky Way appears so prominent in the dark night sky from Earth.
But there is a tremendous part of the Milky Way that we're not able to see with the naked eye, including most of the spiral arms and the far side of the galaxy. This limited view is due to our galactic perspective from within one of the spiral arms, where cosmic dust and gas obscure much of the view.
As for the parts of the Milky Way that we can’t see? Astronomers have other tools, like infrared astronomy and radio telescopes, to observe our home galaxy we can’t see with the naked eye.
Sources
NASA. (n.d.). The Milky Way Galaxy. Imagine the Universe! Retrieved December 29, 2022, from https://imagine.gsfc.nasa.gov/science/featured_science/milkyway/
Rothstein, D. (2015, June 27). How can we see the Milky Way if we are inside it? (Intermediate). Ask an Astronomer. Retrieved December 29, 2022, from http://curious.astro.cornell.edu/about-us/93-the-universe/the-milky-way/general-questions/491-how-can-we-see-the-milky-way-if-we-are-inside-it-intermediate