Caoimhín's Content

In this video we are back to taking a look at something we can see in the sky when the video is published, Orion. Probably one of the most famous constellations in the sky thanks to Orion’s Belt, the three bright stars in the middle, Orion is really coming to the fore in December and January. In the long dark nights of winter Orion is nice and easy to observe. We’ll concentrate on what there is to see in the sky, rather than the mythology behind the Hunter. If you are interested in Greek and Roman mythology, there is a video all about the story of Perseus and Andromeda up on the channel, and we will take a look at the story of Orion in the future. Many features of the constellation are visible with the naked eye, even in the city, and it is those easy features that we will start with.

Orion contains some very bright stars, and the shoulders of the Hunter, Betelgeuse and Bellatrix, as well as the ankles or feet, Rigel and Saiph, form a visible box around the famous trio that make up the belt. Orion extends much further than this, with a club raised above his head and a lion skin hanging from his extended other arm. Those extremities are quite faint and a bit harder to see, a little easier might be Orion’s Sword. In most cities, it is only visible as a slightly fuzzy patch underneath the belt, but that fuzziness is the tell tale sign of our first deep sky object. In the above video, the lines of the constellation are brought up, followed by the image of the mythical hunter, to give you an idea of the full extent.

The Sword of Orion is really a nebula, a cloud of gas in space with some stars in and around it, but a slightly fuzzy star-like object is certainly all we’ll see if we are dealing with light pollution, so we’ll push out to the countryside to leave that glow behind. As soon as we are in a dark location, Orion’s Sword becomes much more obvious, and a lot of fuzziness becomes visible, even to the naked eye. There are a few Deep Sky Objects visible to the naked eye, you can take a look back at the video about deep sky objects if you’d like to learn a little bit about seeing the Andromeda Galaxy or the Pleiades. That video also explains the difference between different types of nebulae, but I’ll go over that here as well.

Nebulae are just clouds of gas in space. Clouds often block out light, and dark nebulae are exactly that kind of dense cloud. A blue colour indicates that the cloud is reflecting star light, where as red nebulae are emitting light themselves thanks to being hot, usually heated up to the point of glowing by some nearby star. Taking only a slightly closer look at Orion, we can see all three types are present. Orion is a fantastic target for long exposure astrophotography for this reason, as the faint glow from the gas clouds get’s more pronounced. Some of the nebulous regions in Orion are visible to the naked eye, so not much magnification is usually needed.

One of Orion’s nebulae is huge, a big red arc of gas all along the left side of the hunter’s form. This shape may be faint, but it takes up a huge part of the sky. This is Barnard’s Loop, a nice nearby example of a supernova remnant. The curve of hot gas that we see here is part of a cloud ejected by a collapsing star and blasted out into this rounded shape. We’ve seen supernova remnants before, but they looked a little more condensed, partly due to their age, but also due to how far away they were, Barnard’s Loop is comparatively closer. It’s so big, you might catch it with your naked eye.

Zooming in on Orion’s Sword will give us a better look at the Orion Nebula, mostly a bluish reflecting nebula, as well as a region where stars form. Travelling up along the Sword into Orion’s belt brings us to a couple of more reddish nebulae. The leftmost star in Orion’s Belt, Altinak, is right next to a very red looking pair of nebulae, the aptly named Flame Nebula, also called the Burning Bush Nebula, and the very aptly named Horsehead Nebula. We can see a lot of dark blobs here against the red, these dense gas clouds are star forming regions as well. The Flame certainly looks fiery, but the Horsehead Nebula must be one of the best named, it really does look like a horse’s head, or maybe a knight from a chess set. Not all nebulae are so obvious, sometimes a good name, or a distorted view through an old telescope, takes precedence over an accurate description. If accurate visual descriptions were the important part, then we’d have a lot of nebulae called “reddish fuzzy blob”, and that would be a real pity, given the name of this next nebula.

A little higher up, still on the left side of Orion, just a bit above the Belt, is a wonderfully mixed nebula, with blues and reds as well as dark clouds. In the blue region at the bottom of the cloud, we can see what might look like a ghostly face. This is the Casper the Friendly Ghost Nebula, and while it does take a fair bit of imagination to see Casper, or any ghostly face really, it is still a nice memorable name.

We follow Barnard’s Loop all the way around from upper left to bottom right, down to the bright star Rigel, and just a little past it to the next wispy cloud of gas. The Witch Head nebula depends on negative space for its name to make sense. the upper left edge of the nebulae seems to outline the profile silhouette of a cartoon witch, complete with bulbous nose and warty chin. It’s a rather easy shape to imagine, though not quite as clear as the Horsehead, and it is a little different from other nebulae, who are normally named more transparently for how they look.

Zooming back out from Orion, there is one more thing to point out, though not a nebula or a deep sky object, or even a constellation. Instead, we have another asterism. The Summer Triangle is no longer a major feature of the sky and will be missing for most of the night. Here we have its wintery counterpart, the Winter Hexagon. We start with the brightest star in the sky, Sirius in Canis Major, and head up to Rigel in Orion. From there we head over to Aldebaran, the eye of the bull Taurus, and then we continue up to the bright Capella in Auriga. From there, we drop down to Gemini and the star Pollux, before continuing down to Procyon in Canis Minor. Then we close the ring by joining back up with Sirius. The Winter Hexagon is a massive asterism, almost too massive to easily see all at once, especially if there are buildings around you, Sirius is rather low in the sky from our perspective here in Ireland, but if you have a clear view and a high vantage point it can certainly be seen.

So that is a little about what we can see in Orion and I hope you get to see some of those things yourselves. We will come back to deal with the mythology and you can expect future videos that also focus on the distant objects that we can see in particular constellations. I hope you’ll join me back here when those videos go up.