Caoimhín's Content

For the latest video, we are taking a look at galaxies again! We had a brief look at galaxies in an earlier video, very generally, where as this time we are concentrating on galaxies that are visible at the moment. As the sky changes from month to month, new constellations come into the sky earlier and earlier, and they bring new deep sky objects with them. Leo the Lion has technically been visible for a few months now, you may remember seeing Venus in the morning with Leo a few months ago. However, I find it’s easier to stay up late than it is to get up early, and Leo has now begun to make its way into the earlier evening sky. We are going to be focusing on the deep sky objects within Leo, so maneuvering to a time of the month when the Moon is out of the way is particularly important.

As with any constellation, Leo doesn’t look exactly like a lion. Many constellations can be tricky to spot, especially in a city sky with light pollution blocking out some of the stars. Some constellations, such as Cancer the Crab, are practically invisible in the city. Luckily, a good number of constellations are visible in the city, and have distinctive arrangements of stars that are easy to recognize. Orion’s Belt of course is one of the clearest features of Orion and Taurus has the distinctive V of the Hyades with the big red star Aldebaran, as well as the Pleiades. Leo is thankfully another such constellation, though it’s distinctive region is a little smaller and harder to spot than the Plough or Big Dipper for example, and is similarly an asterism. The “head” of Leo, the most western portion closest to Orion, forms a distinctive curvy hook shape. It looks almost like a question mark without the dot, and I mention in the video that it looks a bit like an epiglottal symbol from the the International Phonetic Alphabet. If you have the capacity to display IPA symbols, this is what I mean: ʕ the symbol for a voiced pharyngeal fricative, which is commonly epiglottal in languages that have it. This shape is the Sickle, and it is the asterism covering what would normally be the head and mane of the lion. The bottom of the sickle is Regulus, which is conveniently the brightest star in the constellation.

With the lines of the constellations visible, the body of the lion stretches east of the Sickle and tapers to a point at the end. This does look a little like a lion that is lying down, viewed from the side. In the picture of the constellation, the lion is shown standing, with the legs stretching below the stars that are joined together to form the constellation. This may seem a little strange, but the pictures of the constellations often extend a little beyond this line drawings. Furthermore, the boundary of Leo extends pretty far beyond those lines, particularly at the back. The boundaries of each constellation need to fit together like a jigsaw puzzle, ensuring that the entire sky is covered. This helps for naming things or locating things based on their constellation, if there was gaps then there would be parts of the sky without any corresponding constellation to use.

Leo has quite a few galaxies visible in its direction, mostly at the tail but also some towards the head or Sickle. Starting with a view from a city sky, looking towards the tail is the best bet, as it is a slightly more dense region in terms of galaxies. This region of the sky, extending into Virgo, is one of the best places to point a telescope with a wide field of view if you are trying to catch a few galaxies, especially if you aren’t too worried about what ones in particular you are going to see. Even with a smaller telescope, you may begin to see some slightly fuzzy shapes a little fainter than the surrounding point like stars. They will certainly appear fainter than most of the stars, but their fuzzy, diffuse appearance should help you to recognize them. In the countryside they will look a little brighter, but still faint compared to most of the stars. The same fuzzy patches are visible around the Sickle, though they are a little more spread out.

All of these galaxies are a lot easier to see in the countryside, as is part of the reason why this is such a good place to look, the Milky Way. Once we’re in a dark enough part of the countryside, you’ll begin to see the outer limb of the Milky Way stretching down through Orion, significantly West of Leo. Not only are we looking away from the brighter center of the Milky Way, we are looking at an angle away from the rest of the disk stretching behind us. The Milky Way is full of wonderful things to look at, nebulae and clusters of stars, but it blocks our view of anything more distant, such as other galaxies. Looking out in the direction of Leo and Virgo ensures that the Milky Way is out of the way, giving us a good view of these galaxies. It helps that the galaxies in this direction are often relatively close to us, part of the same cluster. Galaxies in space seem to group together into clumps or clusters with relatively emptier intergalactic space in between. As the universe expands, the distance between these clusters grows, but the gravity of galaxies near to each other can still attract them together.

The large number of relatively nearby galaxies gives us a chance to see a huge variety of them nice and close together. A lot of popular galaxies are face on spiral galaxies, where we see the rings. However, spiral galaxies are almost disk shaped, they are pretty flat with a bulge in the middle. This makes them appear very different from the side, which we can see with the Needle Galaxy. Spiral galaxies often have a dark cloud of dust and gas around the outside of the spiral rings. This is hard to see when looking a t a galaxy face on, but from the side the dark region is backlit and highlighted by the glow of the galaxy. That helps to give the Needle Galaxy its sharp, straight appearance. The bulge in the center of the galaxy is generally a lot thicker than this surrounding ring, causing it to stick out on either side, helping to inspire the galaxies other name, the Flying Saucer Galaxy. Another side on galaxy is the Hamburger Galaxy, one of the Leo Triplets. It distinctly has that dark band, which I believe is meant to be the burger patty of the hamburger, with the galactic bulge forming an undersized bun on either side. The other two Leo triplets are right next to it, and even quite powerful telescopes may be able to show all three in one image. The other two are closer to face on, but still at a little bit of an angle. One of them is faint enough that it’s difficult to see the arms at all, though it is easier with the other. It’s hard to tell when looking at a face on galaxy that it has a disk of dust, and of course it’s impossible to see the spiral arms in an edge on galaxy. It’s only by observing both angles that we can get a full picture of how these galaxies are really structured. By learning about these other spirals, we get a better idea of our own spiral galaxy. Of course, spirals aren’t the only type of galaxy.

As we look into the region between Leo’s tail and Virgo’s head, we get to see some of the other types of galaxies, the big round balls, believed to form when smaller spirals collide (for more on that, you can check out the last galaxy video). In Stellarium, a galaxy type code comes up when you click on galaxies, and we can see some here such as S0 for a spherical galaxy, and E1 for an elliptical galaxy. These galaxies may not look as interesting, being huge white balls with out arms or dark bands. However, these galaxies are impressively big, some hundreds of times bigger than spiral galaxies like the Milky Way, and they provide a possible insight into the future of our galaxy, after it fuses with the Andromeda Galaxy.

Moving into Virgo, there is a particularly dense patch, with objects like the Markarian Chain which is composed of many galaxies itself. This region hosts many different types of galaxies, big round elliptical and spherical ones, bright blue grand design spiral galaxies with distinctive arms, like the Virgo Cluster Pinwheel, barred spirals like the Lost Galaxy of Copeland, and spiral galaxies of a more reddish colour. M90 is one such galaxy in this region. M90 has a distinctive warm colour, reds and yellows, rather than the cool blue or white we see with many other spiral galaxies. The reason for this is star formation. Blue stars are generally short lived, blue stars are hotter than red stars. Blue stars, and many other colours, will eventually become red as they age, and red stars, particularly smaller ones, can last incredibly long times. If there are many new stars being formed, enough of them will be young and hot, giving a white or blue colour. If star formation stops, these stars will die out or turn red, and these cooler reddish stars will be all that’s left, giving the galaxy a reddish colour. This may happen due to a lack of hydrogen, necessary for the formation of stars. As galaxies age, this hydrogen gets used up, though it can also be ripped away by passing massive galaxies.

Many galaxies have many names, or even no common name such as M90. The Weaver’s Shuttle Galaxy is an alternate name for the Silver Streak Galaxy, and personally I prefer the Weaver’s Shuttle. Tjis is an edge on galaxy, with a dark band visible along the edge, giving it a narrow appearance. This does make it look like a streak, but if you’ve ever seen the shuttle of a loom zipping back and forth between between the, between the threads, that seems like an even more apt comparison. The nearby Blowdryer Galaxy looks nothing like a blowdryer. It’s a clear spiral galaxy, and its Messier number, M100, is just as appropriate for its shape. The French astronomer Charles Messier catalogued hundreds of deep sky objects, and their number in the Messier Catalogue has become a convenient way to refer to these objects. They are often quite visible, being discovered by an astronomer way back in the 1700’s.

The Messier Catalogue has inspired the Messier Marathon, an all night astronomy event where you try to spot as many Messier objects as possible. It won’t be the subject of the next video, but it may be the subject of a much longer than normal video in the future. Even spending just a couple of minutes on the 110 objects would give a video close to four hours long. There’ll be a fair few typical 10-ish minute long videos between now and then, but it’s something you can look forward to, and I hope you stick around to catch it.