Over centuries of philosophy and research, through the times of the classical astronomers to Galileo’s observations of the Milky Way, humanity’s understanding of our universe has evolved from a simple model of the sun and planets to a vast wheel of stars we now know as our galaxy.

And since the “discovery” of our Milky Way–or, more accurately, the discovery of what that hazy band of stars in the sky is–we’ve come to realize just how massive our home in the cosmos really is.

That scientific journey started with the Herschels’ mapping of what was then called the “star system.” Later astronomers began to realize just how far out from the sun the stars of our galaxy really reached. Determining distances across our galaxy was the first step to discovering its size.

Later, we began to understand its structure–mapping the extraordinarily thin disk, the chaotic central bulge, and the visible part of the halo, a sphere of stars that extends beyond the plane of the galaxy.

And since then, we’ve begun to master the next critical part of understanding our galaxy: its mass.

So, how massive is our galaxy?

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