 Welcome to our final segment on the Milky Way. In this segment, we'll go over our current understanding about the structure and size of the Milky Way as a whole and our place in it. We'll examine the galactic center with its supermassive black hole. We'll go a little deeper into the nature of a black hole and show a few of the stellar black hole candidates we have found. We'll explore the galactic disk with its spiral arms and we'll cover the latest information on the galactic halo. And as usual, we'll discuss how we came to know these things from our viewpoint deep inside the galaxy itself. On January 1, 1990, from its orbit around the Earth, the Goodard Space Flight Center's cosmic background explorer created this edge-on view of our Milky Way galaxy in infrared light. Here's a newer inside image of our galaxy. In fact, it's the most detailed map ever made. It was released in 2018 by Gaia, the European Space Agency spacecraft, that recorded the position and brightness of 1.7 billion stars, as well as the parallax, proper motion, and color of more than 1.3 billion stars. The map shows the density of stars in each portion of the sky. The galaxy has a center with a central bulge, a disk of rotating stars and dust, and a halo without dust clouds and peppered with globular star clusters. The disk is at least 100,000 light-years in diameter and the halo is much larger than that. We'll go into each of these galaxy components, starting with the galactic center. We'll cover how images like these are created from inside the galaxy and how impossible it is to get an image from outside the galaxy later on in this segment.