Caoimhín's Content

In this video, we take a look at Deep Sky Objects, those things lying outside our solar system, or even outside our galaxy, which we can see. Having dark skies with no light pollution helps and most of these objects require telescopes to see at all. From clouds of gas to groups of stars, we’ll take a quick overview of the different types of objects that you can find out there.

As we are looking at deep sky objects, this whole video takes place in a dark sky free from light pollution, and we will be ignoring the Moon and the planets. Most of the objects will will look at occur in or galaxy, or at least around our galaxy. Other galaxies also have instances of the deep sky objects we will observe, but being in other galaxies makes them much harder (though not always impossible) to observe directly.

We begin with nebulae, the clouds of gas and dust we see hanging in our galaxy. There are a lot of types of nebulae, differentiated by where they come from and how they look, which are often connected. Generally, clouds of gas with uncertain origins can be broken up by colour. Dark absorption nebula appear black, obscuring any light beyond them. Pale, bluish reflection nebula reflect the light of stars, appearing bright for a similar reason as planets or the Moon. Reddish emission nebula are hot, heated up by stars until they glow with their own light.

The first nebula we look at is a three-in-one, the Trifid Nebula appears to have its red emission nebula center split in three by dark lines formed by an absorption nebula, all bordered by a pale blue reflection nebula. This is really one big cloud of gas, but different parts are effected differently by the stars inside due to distance and our perspective. It sits roughly in the direction of our galaxies center when viewed from the Earth.

Dense clouds of hydrogen gas, usually warm ones, are often where we find stars forming. These nebulae are unsurprisingly referred to as star forming regions, and above the Eagle Nebula is one such region, featuring spikes or pillars with new stars forming within them. These nebula are eventually blown apart by the light and heat of the stars inside, causing the nebula to become more diffuse and even disappear, leaving behind a cluster of stars.

Star clusters also come in multiple types, starting with young open clusters like the Pleiades or Seven Sisters. After blowing away their originating nebula, young stars are still bound together by their gravity as they drift through space as a group. These groups usually have quite a bit of space within them and are usually well within the galaxy, letting us see them and the empty space within them quite clearly, leading to the name open clusters. As the stars age they often drift apart, pulled away from each other by massive objects, like other stars and black holes.

As stars drift apart and move through the galaxy, some drift towards its edges. Stars orbiting a galaxy may clump together, and the gravity of many stars together can pull more loose stars out of the galaxy. These clumps of older stars are known as globular clusters, and they orbit the galaxy proper like Moons around a planet. Taking a look at the Great Cluster in Hercules, we can see that these clusters get quite dense, making the core of the cluster appear to blend together. These globular clusters are globular and significantly less open than the clusters of young stars that we see.

We have found globular clusters orbiting around other galaxies as well, and here we take a look at the Triangulum Galaxy. The Triangulum Galaxy is close to the Andromeda Galaxy and the next closest galaxy to the Milky Way and Andromeda after each other, making it a fantastic target for telescopes. It is a spiral galaxy like the other two, and another type of deep sky object. Other galaxies also have nebulae, sometimes birthing new young stars, and the next kinds of nebulae left behind after stars.

All stars age, whether they leave the galaxy or not, their nuclear fusion producing heavier elements as they go. These heavy elements do not produce as much energy when they fuse, if they can be fused by the star at all. This causes the star to cool down and swell up, and almost all stars seem to go through this part of the aging process in a reasonably similar way.

Small stars like our Sun eventually fall apart, shedding their outer layers of different elements, and leaving behind a white dwarf. These nebulae are called planetary nebulae due to their round shape, and we will look at the Ring Nebula in Lyra as an example, very close to the star Vega in the Summer Triangle. The Ring Nebula is aptly named, appearing as a circular ring of gas. Really it is more of a sphere, but appears disk like to us, with a white dwarf shining in the center. White dwarfs are still hot from being at the center of an active star, but once the star falls apart the white dwarf begins the slow process of cooling down, eventually ceasing to glow at all.

More massive stars collapse at the end of their lives. The implosion of an ancient star can produce neutron stars or black holes depending on their size. When the outer layers collide at the center, they rebound in a massive explosion, a type of supernova. Supernovae still spread elements out into space, but they often appear more disordered, the shell-like layers mixed together and spread out by the force of the explosion. We take a look at Cassiopeia A or Cass A, a supernova remnant in the constellation Cassiopeia. This kind of nebula can only be created by massive stars, or Sun is instead destined to be a planetary nebula like the Ring in Lyra.

Now that you have some idea of how these different objects look, you might be able to find recognize them through a telescope. Finding them, especially the fainter ones not visible to the naked eye, can be tricky. Software like the Stellarium software I use for these videos often includes a search function, as do some of the smartphone apps you can use to label things in the real sky.

Until next time, I hope you get a chance to see some of these objects and recognize some of the features that I’ve mentioned.