The Hidden Galaxy (Caldwell 5 or IC 342) - Deep Sky Videos

Okay, Professor. — You've been out with your telescope again. — I've been out with my telescope looking at Caldwell 5. Since we're working our way through this Caldwell catalog, and we've got to number five. How lovely is that? — I mean, that is pretty good. — It's a beautiful galaxy. It is the third largest galaxy in the sky. — Oh, okay. So, it was an easy one then. — Yeah, although it's a galaxy that no one's heard of for it. It's not, you know, the famous ones like the Andromeda galaxy, the biggest one in the sky everyone's heard of. No one's heard of IC 342. — What's the second biggest one in the sky? — M33, the Triangulum galaxy, non-spiral galaxy. — And then this one, has this one got like a cool name like the dragon or anything? — It's sometimes called the hidden galaxy for reasons which we'll come to. But, yeah, it's not a particularly well-known galaxy. So, you remember the galaxies are generally put into catalogs, and most of the famous ones, some of them are in the Messier catalog, but actually most galaxies don't make it to the Messier catalog. They're in a thing called the New General Catalog, which is why a lot of them are called NGC something or other, which was a catalog compiled kind of towards the end of the 19th century. This one didn't make it into the NGC. It was too late. So, after the NGC was made by a guy called Dreyer, and I think it was published in 1888, he published a couple of kind of supplements to the NGC that were called the Index Catalog or the IC, and this made it into the Index Catalog. — Wow, third biggest in appearance to us, not third biggest in actual size. — No, third biggest in angular size. It's kind of a It's a little bit smaller than the full moon. — Okay. What do you want to tell me about it? — I'll tell you Well, let's go back to its discovery. As I say, he cut slightly missed the boat in that he didn't make it into the NGC. That's because it was discovered in Let's get the date right, 1893 by a guy called William Denning, who was an amateur astronomer. So, the reason why kind of various things didn't sort of quite make it into the NGC, but then there were a whole bunch of more galaxies were found, is really because photographic astronomy was coming along at that point. So, people were taking photographs of things that hadn't made it, you know, weren't really that visible just through telescopes, but as soon as you started taking pictures, suddenly you could see much fainter things. This galaxy is a bit interesting cuz it wasn't a photographic discovery. Um it was an optical discovery, which is the discovery of somebody looking through an eyepiece by this amateur astronomer from Bristol in the UK who was mainly looking for comets and he was interested in meteor showers and all sorts of things he's quite famous for, but in one of his sweeps for looking for comets, he found this galaxy. And it was published in this short-lived journal called Astronomy and Astrophysics. There's a current Astrophysics without the hyphen, but there was this short-lived journal at the end of the 19th century. So I sort of dug down and managed to find the original copy of his claiming to have discovered this galaxy and it's quite entertaining cuz it's this wonderful piece of um passive-aggressive writing, I think it's fair to say is the way to describe it. It's nice to know that astronomers haven't actually changed in the last 100 or so years. So let me read a bit from this. It says, "Professor Swift writes in the August number of Astronomy and Astrophysics about a new nebula independently picked up by Professor Barnard and myself. " some coordinates. Blah blah. He claims to have seen this nebula many years ago with his 4 and 1/2 inch comet seeker. My purpose now is not however to discuss the question as to priority of discovery, but to mention that while hunting for comets, I found another one. So basically he's you know, wants to just put it on the record that he actually found that other object as well, but actually he's past that now. He's not going to raise that again even though he's just raised it again. And here's this other object that he found in passing. And then he goes on to describe it. He talks about this new object he found. It's rather faint with a nucleus about 12 magnitude and very small. It's kind of interesting cuz I just told you it was the third largest galaxy on the sky, but it was sufficiently conspicuous to be discovered with his 10 inch reflecting telescope and then he goes on to give the coordinates of the right ascension and declination of where it is in the sky. Turns out the coordinates are quite important for this galaxy and so that's where they were and again I went and checked and indeed that's exactly where this galaxy is on the sky. What's going on? Why has it been so elusive? So it actually interestingly it kind of comes down to its coordinates. And so, there are various ways you can measure where something is on the sky. Basically, you know, you need some way of saying left to right, up and down. You just basically need two coordinates to specify where something is on the sky. So, the ones that astronomers typically use, and so the ones that we used in this discovery, are these things called right ascension and declination, which are essentially related to the Earth. They're to do with how far north or south the thing is relative to the Earth, and how far east or west, having to allow for the fact that the Earth rotates, which complicates things a little bit. But basically, it's a sort of Earth-based coordinate system. There are other coordinate systems that astronomers sometimes use. For example, sometimes they use this thing called ecliptic coordinates, which is a measure relative to the solar system. Essentially, it's how far along things are in the plane of the solar system, or how far out of that plane they are. That's useful for measuring planets and asteroids and those kinds of things. But there's another coordinate system, so I looked this up in this other coordinate system. So, here are the various ways you can measure the coordinates of this galaxy. So, we talked about right ascension and declination, and there were these ecliptic coordinates, but the one I wanted to talk about are galactic coordinates. So, another way you can measure where something is in the sky is you can set your zero point for your coordinate system to be the center of the Milky Way, and then you can measure how far out of the plane of the Milky

Way they are, or how far along are. And again, that gives you these two directions. And so, in this particular case, this galaxy is at a galactic longitude, that's how far along the plane it is, of 138 degrees, but a galactic latitude, that's how far out of the plane it is, of only 10 degrees. So, it's very close to the plane of the Milky Way, and that's why it wasn't discovered for so long. Because close to the plane of the Milky Way, you've got all this dust, all this obscuration, all this material, which makes anything that lies behind it appear very faint. So, that's why when this object was discovered, it was small and faint, cuz you could only see a little bit of light from the center of it. — So, you're look what you're saying is like basically, you're looking through a big, thick chunk of the Milky Way, like almost looking straight through the whole thing. — Absolutely. I mean, you're 10 degrees out, so you're not quite in the plane of the Milky Way, but even so, that's looking through a lot of Milky Way. And in fact, you can sort of see that just by looking at it cuz there's an awful lot of stars here. And these are just stars from the Milky Way that you're looking through. But not only are you looking past the stars, but you're looking through all this dusty material. — So, Denning wasn't seeing much of it. He didn't realize just how big a thing he was looking at. — Right, because he didn't have the luxury of integrating for a long time by taking a picture. He was really just looking through his eyepiece. And with the eyepiece, even with a moderately large telescope he was using, you really can't see much of this galaxy. It's only when So, I think this was a 2-hour exposure I ended up taking. It's only when you take a relatively long exposure of it, you see quite what a big, dramatic galaxy it is. It's about the same size as the Milky Way. So, it's actually kind of a twin of the Milky Way. — Nice. — I mean, it's not really a barred galaxy. The Milky Way has a one of these sort of rectangular barred structures in it. But other than that, in terms of it's a spiral galaxy, it has roughly the same kind of a spiral structure as the Milky Way. It's the same luminosity as the Milky Way. So, it's pretty much at least a close cousin of the Milky Way. — One last question. It's in the Caldwell catalog, and we've discussed the Caldwell catalog before that Patrick Moore cataloged these objects that he thought were good to look at. They were good sport. This sounds like this isn't though. Unless you're using the tech that you were able to use, this isn't one you're going to have fun in the backyard with, is it? Like, you're not going to see much. — You can just about glimpse it with a telescope just with an eyepiece. But I think the Caldwell catalog was at least in part designed with taking pictures in mind. So, actually, yeah, it And it's big enough that if you're prepared to look for long enough, it does make a pretty dramatic picture. It is a beautiful spiral, I don't deny it. — Mhm. — So, yeah, for all purposes, you know, I'm going to be traveling around the solar system with my dad, which is kind of nice, really, isn't it? — It is nice. Have you looked up anything more about them? Are they big? Are they small? Are they Is there anything about them that's special? Are they pretty, you know, run-of-the-mill, average Joes? — I mean, what's interesting about them is they're both very similar. They're on very similar orbits. They're very similar sizes. I think they're estimated to be about 6 or 7 km across each.