 Greetings and welcome to the Introduction to Astronomy! One of the things that I like to do in each of my introductory astronomy classes is to begin the class with the astronomy picture of the day. From the NASA website that is apod.nasa.gov.apod. And today's picture for November 20th of 2023, well, it is titled the Horsehead Nebula. So what do we see here? Well here we see the nebula known as Barnard 33, which is a dark nebula, a dark dust cloud blocking out the light from behind it. And this is more commonly known as the Horsehead Nebula for its distinctive shape that looks like perhaps the night piece in a game of chess. And that is again a dark nebula that is dark dense areas that are blocking out the rest of the light from behind it, and just happens to have something resembling that kind of shape. Now the darker, denser material will be in the process of forming stars, and the Horsehead Nebula is within the Orion Star-forming region. So we are seeing stars that would be forming in this region again. Now we also see, in addition to the dark nebula, we see another nebula down toward the lower left, and that is an example of a reflection nebula. A reflection nebula occurs when a bright star has formed and still has dust around it, not as dense as within the dark nebula, which completely hides material from view, but still some dust around there, and the dust is very good at scattering the shorter wavelengths or blue light, giving it a distinct blue color. As we see in our image today. So those are two of the prominent types of nebulae that we see within a star-forming region. The third we see all around, and that is the red glow of hydrogen gas, and we call that an emission nebula. So we see all three of these different nebulae, and they would look very different as we study them, but they're all related with star formation. The dark dense areas are where stars are currently forming. Then we have the reflection nebula, which has young stars where the light is being scattered off of dust grains remaining, and then the red glow is the scattered hydrogen gas around the whole region that is energized by ultraviolet radiation from those hot stars that have recently formed and caused to glow. And when hydrogen gas glows, it gives off a distinct red color as we see in our image today. So again, all of this is part of the Orion star-forming region, which is a nearby star-forming region, in fact, one of the closest to us here on Earth. So that was our picture of the day for November 20th of 2023. It was titled The Horsehead Nebula. We'll be back again tomorrow for the next picture, previewed to be Supernova Wisp. So we'll see what that is about tomorrow. So until then, have a great day, everyone, and I will see you in class.