2026 March 11 - CG 4: The Globule and the Galaxy

0:00Greetings and welcome to the Astronomy Picture of the Day podcast. Today's picture is titled CG4, the globule and the galaxy. So what do we see here? Well, here we see a galaxy off to the left and it may look like it is about to be consumed by a giant space creature approaching it from the right-hand side. And of course, these are actually two very different objects very far apart in space. They just happen to look close together on the sky. And one thing we have to remember there is that we lose the three-dimensional image when we look out onto the sky. It looks like everything is in a great celestial sphere around Earth. And that everything is at the same distance. We don't really see that perspective here. How do we tell what is closer and what is farther away here? We can see stars, we can see gas, we see our globule, and we see a galaxy.

1:02Well, we know that galaxies are farther away, but just by looking at it, you really can't tell that. Now, the galaxy itself is more than 100 million light-years away, which is a much greater distance than the mere 1,300 light-years for the cometary globule. Now the cometary globule here to the right-hand side, so named because it may resemble a comet with a head here to the left and a tail stretching back off to the right. Of course, it has nothing to do with comets, which would be part of our own solar system. And this is well beyond our solar system over 1,000 light-years away. Now the globule itself is what is known as a molecular cloud. That is a denser area in space where molecules can form. Normally out in space, you don't form molecules, atoms combining together. And that's because space is filled with high energy particles, high particles themselves,

2:08light, things that will rip molecules apart. So they won't last for a very long time if they form, unless they're shielded. So forming within something like this where material is denser, then shields that from the external energy and allows molecules, and in fact, in some cases, very large, complex molecules to start to form. And we can see some of those when we study molecular clouds like this in, say, the radio part of the spectrum, which is where a lot of molecules will emit their energy. That allows us to detect various complex molecules in regions such as this. Also within those dense knots, stars begin to form. As denser areas form and molecules form, more and more material will start to clump together. And the densest knots here are likely in the process of beginning to form stars. So here we see a galaxy that appears as though it's going to be eaten, even though it isn't,

3:13by a cometary globule, which really isn't a comet in any sense, but a molecular cloud and star-forming region. So that was our picture of the day, titled CG4, the globule and the galaxy. We'll be back again tomorrow for the next picture, previewed to be Uranus. So we'll see what that is about tomorrow. And until then, have a great day everyone, and I will see you in class!