字幕表 動画を再生する 英語字幕をプリント happy Halloween. 60 symbols viewers. Okay, so Halloween is upon us on dhe surviving Carson around looking for something suitably astronomical. What's celebrates Halloween so are stretched today is to talk about the witches broom nebula because some people think it does resemble a witches broom, perhaps out of Harry Potter. I don't quite see it so much, but, uh, I other people do well, in this case, we're looking at a supernova remnant. So this is the expanding shock wave from a star that probably exploded, or 5000 and 8000 years ago. When a star explodes, it sort of throws its guests out into space on that gas, then interacts with the interstellar medium that's already out there on Heated up on makes it glow. So you have this big, almost spherical ball sphere, so hollow sphere of material that's glowing. That's how far the explosions got on one of the sections of this. You think about us. Fear the bits that you're seeing. A John you'd be looking right through my hand right there. You're seeing face on you just be seeing through my hand. Whereas here you'd be seeing the full width of my hand So actually, you see the ages much more clearly because you're looking through more stuff. And the witches broom is one small part of a much larger nebula called the Veil Nebula, which is actually quite large. It's about three degrees across. And to put that in perspective, your thumb outstretched covers an AnAnd Gle of about two degrees on the sky. So it's slightly larger than your outstretched thumb. And when you think about it, the full moon itself is only half a degree, So this is actually quite a large object on the sky. It's really like a bubble. Words like a big bubble you're looking at is not perfectly spherical bubble, because different bits of expanded by slightly different amounts. But basically it's a big, big, hollow sphere you're looking at. You're talking about anything which is expanding at sort of 1000 kilometers per second or thereabouts. It's cracking along at a fair old speed, and that's the reason why it glows at all is because you got this material. It's expanding outwards and basically smacking into the material is there and shock eating it. So it's only because there are these very high speeds involved that the thing gets hot enough to glow in the dark. It is quite bright, but that brightness is spread out over this very large area, which means its surface brightness is actually quite low. So it's very difficult to see and in fact what you are seeing. If you look closely at the pictures, you're seeing these sort of phylum entry rope like structures. The shockwave has hit this diffuse gas, and although it's happening in a three dimensional shell, you're really only seeing it when, when you look down enough of it that it becomes visible. And that only happens on the edge. When you're looking down a fair amount of material along the line of sight, it's just chance. So if you look at enough places in the sky, you'll start picking out shapes, and this one just happens to end up looking like a broomstick. If I was in a spacecraft like the space shuttle and I flew into the the Shockwave, I flew into this thing head on, which looks like this big, beautiful, gentle thing. Any any ideas what to expect, what I go through it, like flying through a cloud. It would be good night rain. It's a good question as one of those tricky ones that you'd have to do a lot of calculations to figure out in detail. My guess would be You probably wouldn't notice, because the density is pretty low. I mean, still pretty much the vacuum of space. It's only the only reason you see it because you know it's spread out over a huge area. It's over that huge area. There's an awful lot of atoms. So there's another one called the Which Head Nebula, which is in some ways it's the same kind of thing. It's another of these clouds out there in space, which looks remarkably like a witch. His head. I think this is one of those cases where the human eyes really good at picking out faces, even where there isn't anything to see you like that famous face on the moon and those kinds of things on. So this is Ah, this is that kind of feature that this Ah, a face like object in the cloud on really what you got. There is a thing called a reflection Nebula. You got a relatively bright star, right jewel nearby, and then it's just this cloud of gas next to it on the light from right, always lighting up the cloud and then some of that light is, is just being absorbed by the cloud and then re emitted in our direction. So if that's a rather blue ish sort of tinge to it, which also adds to its vaguely witchy, spooky nature. But the reason for that it comes out the shade of blues and start interesting piece of physics. Which is that the right jewel, the star that's lighting it up? Of course, it's emitting light from all across the spectrum. Red light, green, light blue light. But the red light tends to go straight through. It's only the blue light that gets scattered towards us, and in fact, it's the same kind of physics is why the sky looks blue when you look at the sky. Because, of course, when you're looking at the sky, you're seeing scattered sunlight on sunlight gets more scattered by the molecules in the atmosphere at the blue end of the spectrum than the red end of the spectrum. On here, it's the same kind of physics, but here, what's doing the scattering is actually dust grains, little dust grains. But they have the same property that they much more to scatter blue light than red light. Red light goes straight through the blue like it scattered the warders. The howling itself is actually an astronomical date. It's known as a cross quarter date in the calendar, so it's halfway between the equal Knox and the winter solstice. So the equinox being where there's equal amounts of day and night, the solstice being the longest night of the year. And so this is halfway in between, and traditionally it kind of marks the beginning, the real beginning of winter.