 Greetings and welcome to the Astronomy Picture of the Day podcast. Today's picture for February 12th of 2024 is titled HFG1 and Abel 6, Planetary Nebulae. So, what do we see here? Well, looking toward the direction of the constellation of Cassiopeia in the northern sky, we see two examples of Planetary Nebulae. Now, a Planetary Nebulae is what happens at the end of the life of a star much like our own sun. And when we see the Planetary Nebulae, we're looking at the outer layers of that star which have expanded. Now, eventually our sun will expand, the core will begin to contract as it uses up its hydrogen, and the outer layers will expand outward. So, eventually it will fill much of the inner solar system up to and including our Earth. And at that point it becomes a giant and maybe later a super giant star. And as it becomes this, at the very end of its life it is unstable. It is not very hard for those outer layers to escape, so any instabilities can push that material out into space. And that's what we will see as the Planetary Nebulae is just the outer layers of the star expanding outward into space. They glow because the core left behind is emitting a lot of ultraviolet light which causes the area to glow and causes those gases to glow. Now that only lasts, that period only lasts a short amount of time. And that's because as that central core cools off and becomes a white dwarf star, it will stop emitting as much ultraviolet light and eventually will not be emitting enough to be able to energize the Nebulae. The material will still be there and will continue expanding out into space. We just won't be able to see it anymore because there is nothing to energize it and cause it to glow. In general, gases are clear. We can see straight through them much as we see through our own atmosphere. However, when they are excited, such as when you put gases in a neon in a tube and energize it, it can start to glow. So that's really what we're seeing here in these planetary Nebulae. Now in the lower nebula, the one known as HFG1 is actually part of a binary system and we can also see shock waves of the material. You can see that blue glow which is a shock wave as this moves through the interstellar medium. So it will pick up that, as it's crashing into that, we see the shock wave and it's moving incredibly fast. So this whole nebula is moving at a speed given here as about 300 times faster than the fastest train in existence on Earth. And that gives us that shock wave in the direction in which it's moving. And that, again, that is energized by the energy, the motion or kinetic energy of the nebula as it moves through space. So that's a different way it glows as compared to the nebula itself. So eventually we could be left behind as this cools off. If it's still moving through this portion of space, then the planetary nebula itself may disappear, but the shock wave could remain and still be visible around this since they are caused by two different processes. So here we get to see two different planetary nebulae in the same portion of the sky and get a little bit of a preview of what our sun might look like many billions of years from now. So that was our picture of the day for February 12th of 2024. It was titled HFG1 and Abel 6, Planetary Nebulae. 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.