Spirals in Space - Sixty Symbols

0:01 [music]

0:10 Professor Jim, what do we got today?

0:12 What do you want to talk about?

0:13 So, we've got another edition of one

0:15 of these things is not like the other today.

0:18 So, I have three pictures here.

0:19 Maybe I'll let the viewers linger for a moment

0:22 and see if they come up with their own ideas.

0:25 Definitely got a like spiral galaxy look happening here.

0:28 So, spiral galaxy is a good guess because we have

0:31 made literally hundreds of videos on objects that look like these.

0:34 And in fact, two of these objects are spiral galaxies.

0:38 So, the usual thing that we talk about collections

0:40 of hundreds of billions of stars and gas and dust,

0:44 beautiful spiral pattern way out in the distant universe.

0:49 But one of them is a more local phenomenon.

0:52 It's this one.

0:53 It is a bit more diffuse that is.

0:54 a bit more diffuse, but it it it could pass for sure.

0:58 And indeed, this is something that rather than being a tiny tiny thing

1:02 that you need a telescope to see very faint in in the sky,

1:05 this is one of these "Oh my god,

1:08 what is that thing in the sky?" kind of phenomenon.

1:11 And it's something that's happening more and more frequently.

1:14 And that's because rather than being an astronomical object,

1:18 it's an atmospheric object.

1:20 And in fact, it is formed from the condensation

1:24 of propellant from the upper stage of a rocket launch.

1:28 And because these rocket launches are happening more frequently,

1:32 and because so many more people carrying around

1:34 phones and video cameras in their in their pockets,

1:37 we now regularly get stories and images and videos

1:41 of these phenomenon being seen in the sky.

1:45 One of the first ones I ever saw was actually this one,

1:48 which was pretty spectacular.

1:50 This happened in Norway in 2009.

1:53 And I have to be honest,

1:54 I am not sure what my reaction would be if I saw that in the sky.

1:58 I hope I would put my logical brain on and say,

2:01 "Something interesting is happening up there.

2:03 I wonder what the physics is behind that." What would your illogical brain say?

2:06 My illogical brain would be be thinking, "My god,

2:09 that's a portal to another dimension or we're being visited by aliens."

2:13 [laughter] So, what's there to say about this?

2:14 What's going on?

2:15 Why doesn't every rocket do it or what makes

2:16 it happen or what what are we looking at?

2:18 So, to see a phenomenon like this, you need a couple of criteria to align.

2:24 If you're going to view it from the Earth,

2:25 you need to be viewing it at the right angle.

2:27 You need to be viewing it at the right time.

2:29 Usually around twilight cuz what you're seeing are ice

2:32 crystals that are reflecting sunlight in the very upper atmosphere.

2:36 It's a very short-lived phenomenon,

2:37 so you need to see it uh shortly after the rocket has launched.

2:41 The kind of rockets that produce this are two-stage rockets.

2:45 And I meant to bring a rocket and I forgot.

2:46 Do you have any dry erase markers here?

2:49 Right.

2:50 So, the kind of rocket that produces this is a two-stage rocket.

2:54 So, it's got two separate stages,

2:56 each with its own fuel supply and its own engine.

3:00 The first stage, the booster, is responsible for getting it up.

3:04 So, getting it to a sufficient velocity and a sufficient altitude,

3:08 and then it's done its job, and then it usually detaches.

3:11 This first stage then falls back to Earth.

3:14 And and now, technology is sufficiently sophisticated that it

3:17 can be caught and reused and used again another time.

3:21 So, now we've got the second stage, which is carrying the payload,

3:25 the thing that you're actually trying to get into orbit.

3:28 This engine ignites, and the job of the second stage is

3:31 to get the payload into the appropriate orbital parameters,

3:35 wherever it's meant to be.

3:37 Sickness separation confirmed.

3:39 When that happens, payload goes off and does its thing.

3:42 Now, you are left with the second stage.

3:45 This isn't going to be reused, so it's got to come back down to Earth,

3:49 but it's got to come back down to Earth safely.

3:51 So, it's going to have a little bit of leftover fuel,

3:54 little left leftover propellant because you always build in a margin of error.

3:59 We don't want to leave it in the stage

4:01 because uh of risk of over pressurization, could explode.

4:07 If it explodes, you've spread debris all

4:09 over that uh that level of the atmosphere, which is very very bad.

4:13 So, the next job for this stage is to get rid of that excess propellant.

4:18 And so, yes, the rocket is often spinning to stabilize it.

4:22 The excess propellant, uh which would be liquid oxygen and uh

4:27 refined rocket grade kerosene in most cases,

4:30 not all cases, um will be uh ejected often from the side.

4:35 And as it spins, this propellant comes out.

4:38 We're now up several hundred kilometers, so we're in near vacuum.

4:42 This uh this propellant comes out, and it immediately freezes.

4:47 And so, most of these phenomena

4:48 that you're seeing are pretty much frozen oxygen.

4:51 So, the liquid oxygen, the oxidizer for your engine,

4:55 that propellant being sprayed out while

4:58 the rocket is traveling forward and spinning.

5:00 And so, it it travels very rapidly, but it also diffuses very rapidly.

5:05 Don't have an exact time scale,

5:06 but it's not going to last a very very long time.

5:09 And it's also going to appear to be

5:11 moving across the sky as the rocket travels away.

5:14 So, you're seeing something in the sky that's both rotating,

5:19 changing, and moving across the sky.

5:22 And none of those things are are are usually what

5:24 we expect to see when we look up in the sky.

5:27 This doesn't sound good for the environment.

5:30 Like, should we be worried about this?

5:31 So, the answer is no, not really.

5:34 Um we're talking about a few,

5:37 maybe a 10 kg of propellant left over from, you know,

5:43 a ton, ton and a half uh in that stage.

5:46 It's not burnt, it's unburnt.

5:48 So, it's it's not been a product of combustion.

5:52 And it really is dispersing up into the level

5:55 of the exosphere where you're at full vacuum.

5:58 So, it's just being spread out, and then uh probably sublimating very quickly

6:02 because of the the solar uh radiation.

6:05 So, in that sense, it's not so bad.

6:07 What is worth considering though is the products

6:09 of all of the combustion that took the rockets

6:12 up to that stage and the number of rockets

6:14 that are now being launched on a regular basis.

6:16 I'm not going to quantify that in this video,

6:19 but it's something that as we develop into a more spacefaring species,

6:23 it's just something that has to be accounted for.

6:25 All right, what are you going to show us now?

6:27 Okay.

6:27 Well, since we're here, since we're in the the physics department,

6:31 it's always fun to play with liquid nitrogen.

6:33 Um so, we've got Paul here who is a wiz with liquid nitrogen,

6:38 and I know he's got a demo up

6:40 his sleeve that really illustrates this in a fun way.

6:43 So, I'm going to hand over to Paul.

6:45 Let's do it, Paul.

6:47 So, first we're going to fill it up with propellant,

6:50 which in this case is liquid nitrogen.

6:53 So, it's very cold, so it's turned into a liquid.

6:56 Okay, that's probably about enough.

7:00 Once we take that out of the liquid,

7:02 the liquid immediately wants to boil and expand.

7:06 And so, when we put it down,

7:07 the two little holes on either side turn into little mini jets,

7:12 and the liquid is propelled out,

7:14 and we see this condensing vapor in these beautiful spiral patterns just like

7:19 we see with the venting propellant from the rockets in the upper atmosphere.

7:33 on the globe.

7:33 Yeah.

7:33 But how would a compass needle know

7:35 to point at the geographic north or south pole?

7:39 In fact, they don't.

7:40 The magnetic North Pole and the magnetic South Pole

7:43 that our compasses point towards are actually in a different place altogether.

7:47 And in fact, that place actually moves.

7:49 So, to understand what's going on here,

7:50 you really have to understand how the magnetic field

7:53 of the Earth is formed in the first place.