The Milky Way
![[url=https://pixabay.com/en/milky-way-rocks-night-landscape-1063305/]"Milky Way"[/url] by skeeze is in the [url=http://creativecommons.org/publicdomain/zero/1.0/]Public Domain, CC0[/url]](https://www.geogebra.org/resource/e2mgsvdr/LWMjCoFEFsVeKa8l/material-e2mgsvdr.png)
On a dark and moonless night if you look at the sky you can see evidence that we live in an arm of a flat, spiral galaxy. The evidence is a thick band of stars traversing the sky as seen in the photograph above. While a camera was used to gather more light than we can with our naked eyes in order to take the photo above, I have seen views almost as spectacular with my own naked eyes from high-altitude desert regions. The name of our galaxy, given by ancient astronomers, is the milky way.
The milky way is disc-shaped with spiral arms. It is around 100,000 ly in diameter and 200 ly thick. It contains around 100 billion stars, one of which is our sun. Our sun is located near the edge of one of the spiral arms. This is essential to our survival. Inside the arms are many energetic events that would end delicate life on earth. Near the center of the universe is a black hole surrounded by other energetic stellar processes that would make the core of the milky way uninhabitable as well.
We find ourselves in a location that is prime for survival and for doing science - two things which seem to have no logical connection, but which are true of our circumstance on earth across many disciplines of natural and physical sciences. This is noteworthy.
As an example, our solar system's location near the edge of a spiral arm near the outskirts of our galaxy is important in two unrelated ways: It allows for survival of biological life since we are far-removed from the energetic supernova explosions within the arms and the high radiation levels of the black hole at the galaxy's core. From other locations, we could neither survive nor learn about the shape of our spiral galaxy.
Photos like the one above could not be taken within a spiral arm or near the core. From those locations all directions in the sky would be uniformly filled with stars of our own galaxy. Views of any distant galaxy would necessarily be obstructed by stars in our own. In this sense a location that allows us to survive also allows us to do science and determine the extent of our universe and the structure of large astronomical objects including galaxies like our own.
Closer to home, the fact that we have a moon that is almost exactly the angular size of the sun in the sky makes solar eclipses possible in which only the luminous edge of the sun becomes visible. It is under these circumstances that we learned about solar spectra and composition as well general relativity in which the eclipse allowed for the testing of starlight being deflected by the sun's gravity. So having a large moon in the sky afforded scientific discovery which otherwise would be difficult or impossible.
That same large moon plays a role in the regulation of the earth's axial rotation - stabilizing it against gravitational precession - which is required for long term regulation of seasons and climate. The moon also controls tides and is thought to have possibly been essential to the formation of complex life and diversification of species.