The size of the Milky Way Galaxy, our home galaxy, is estimated to be around 100,000 to 120,000 light-years in diameter. However, it's important to note that this measurement is not an exact value and can vary depending on different estimates and observational techniques.
The idea that the size of our galaxy is coincidentally 100,000 light-years across is a misconception. In reality, the size of the Milky Way is not determined by any specific cosmic constant or mathematical principle. It is a result of the natural processes that govern the formation and evolution of galaxies.
Galaxies form through the gravitational collapse of vast clouds of gas and dust in the early universe. The size of a galaxy depends on various factors, such as the amount of matter available, the rate of star formation, and the merging of smaller galaxies over time.
The estimate of the Milky Way's size is based on observations of its structure, including the distribution of stars, gas, and other components. Astronomers use different methods, such as measuring the rotation of the galaxy and studying the motions of stars within it, to estimate its size. These measurements involve uncertainties and assumptions, leading to a range of values rather than an exact figure.
It's important to approach astronomical measurements with an understanding that they are subject to revisions and refinements as our observational techniques and understanding of the universe improve over time.