 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 slash apod. In today's picture, for September 18th of 2023, well, it is titled The Red Sprite and The Tree. So, what do we see here? Well, here we see two very different objects. In the foreground we see a tree, and in the sky we see an example of red sprite lightning. Now, there may be some similarities in terms of how they appear, especially in that we see the tendrils stretching down from the lightning in many ways, much like the branches stretch upward from the tree. However, the lightning is something occurring within our atmosphere, and it's a very unusual type of lightning, and in fact, one that had been seen for a long time, but had not been very well known and very well understood. In fact, there are reports of it going back to the late 1800s, but it was not actually photographed until 1989, and since then, many times it has been captured, but it's a very elusive type of lightning, very difficult to catch, one of the reasons that it has its name of sprite lightning being difficult to detect. Now, when we look at it, it's kind of a different type. This one looks almost like a jellyfish perhaps, with the kind of a blob on the top, and then the tendrils coming down below. Now, but even though it looks like it's rather close to this tree, it is not, it is very high up in Earth's upper atmosphere, and it is a type of lightning much like any other, much like other lightning that we get, it can be associated with thunderstorms, and in fact is often well above those storm clouds, which are much closer down to the ground. So, while you can see some clear skies here, we're close to the region around that sprite lightning, it is really well beyond, and actually probably out over those storm clouds, off in the distance. Now, these can be very fast moving, so when the discharge begins to occur, the lightning in those tendrils can move downward at a large fraction of the speed of light, about 10% the speed of light. So, they zip down there very quick, very quick, and we see that excitation within the atmosphere from the discharge. But again, it's only a fleeting view that we get of these, so you have to be looking for the right conditions as to when they might occur, and then take some very fast frames to be able to hopefully catch some of the red sprite lightning that can occur in Earth's upper atmosphere. So, that was our picture of the day for September 18th of 2023. It was titled, The Red Sprite and the Tree. We'll be back again tomorrow for the next picture. So, until then, have a great day, everyone, and I will see you in class.