0:21:06 > 0:21:08This is Blue Peter, but mini.
0:21:08 > 0:21:10Expect epic adventures,
0:21:10 > 0:21:12makes, bakes, badges, pets,
0:21:12 > 0:21:14presenters and your host.
0:21:14 > 0:21:17We've only got five minutes, so get ready for your Blue Peter adventure.
0:21:19 > 0:21:21Time. It's constantly ticking, isn't it?
0:21:21 > 0:21:23And we use it every day, we use it to organise our lives
0:21:23 > 0:21:26and our schedules and it kind of keeps us all in sync.
0:21:26 > 0:21:29Sometimes it even lets us know when we're a little bit late for school...
0:21:29 > 0:21:31You know who you are.
0:21:31 > 0:21:33Erm, so if I'm going to talk about time, I'm going to need a clock.
0:21:33 > 0:21:36But this is Blue Peter, so I'm not going to use any old clock face.
0:21:36 > 0:21:40I've brought you to see the most famous clock in the world.
0:21:40 > 0:21:42Ha-ha. Oh, yes.
0:21:44 > 0:21:48We've been invited to parliament to help with a very special task.
0:21:48 > 0:21:49The changing of the clocks.
0:21:50 > 0:21:53Taking me through each important stage in the process
0:21:53 > 0:21:56are the clock mechanics, Ian, Hugh and Paul.
0:21:58 > 0:22:01All the work happens at the top, which means climbing 334 steps.
0:22:03 > 0:22:06This is one of those times when you've got to speed the film up.
0:22:06 > 0:22:08'I'm actually climbing Elizabeth Tower.
0:22:08 > 0:22:10'The name Big Ben refers to the bell at the top.'
0:22:10 > 0:22:11BELL RINGS
0:22:11 > 0:22:14But why do we change our clocks in the first place?
0:22:14 > 0:22:16To explain that, we need to go into space.
0:22:18 > 0:22:20The earth is tilted as it orbits the sun.
0:22:20 > 0:22:22During the summer we have longer days
0:22:22 > 0:22:24because we're facing towards the sun
0:22:24 > 0:22:26and in the winter we have shorter days
0:22:26 > 0:22:27because we are facing away from it.
0:22:29 > 0:22:32A British builder called William Willett first suggested the idea
0:22:32 > 0:22:35of changing the clocks in 1907 in order to make
0:22:35 > 0:22:37the most of our daylight hours.
0:22:41 > 0:22:44'Phew! I'm finally here.'
0:22:44 > 0:22:47- Here it is, the great clock of Westminster.- It is great, isn't it?
0:22:47 > 0:22:48Look at that.
0:22:48 > 0:22:50It may not look like the clocks you have at home,
0:22:50 > 0:22:53but this 161-year-old mechanism turns the hands
0:22:53 > 0:22:55on the world-famous clock face.
0:22:55 > 0:22:57It weighs a whopping 4½ tonnes.
0:22:58 > 0:23:01That's the same as a fully grown elephant.
0:23:01 > 0:23:03Now, we know Big Ben is the sound that you hear,
0:23:03 > 0:23:06but the bit that you recognise of course is the clock face
0:23:06 > 0:23:07and we're actually behind it.
0:23:07 > 0:23:09It's huge, it's massive, isn't it? Do you know how big?
0:23:09 > 0:23:13Seven metres across. And you've got 312 panes of white glass in it.
0:23:13 > 0:23:17This is our inspection hatch, we can actually look outside,
0:23:17 > 0:23:19make sure that there's no panes of glass broken.
0:23:19 > 0:23:21I think maybe we should probably inspect the outside
0:23:21 > 0:23:24and have a quick look while we're here, you know.
0:23:24 > 0:23:26Lovely view of London.
0:23:26 > 0:23:29Oh, I can see our camera crew down there. Hello!
0:23:29 > 0:23:30Now, you see that is just awesome.
0:23:30 > 0:23:32Now, we can't get this camera out there
0:23:32 > 0:23:34to show you what the view's like,
0:23:34 > 0:23:36but I have one of these little cameras that will do just the job.
0:23:36 > 0:23:38So, have a look out here.
0:23:38 > 0:23:43That is me hanging out of this huge monument in London.
0:23:43 > 0:23:45Isn't it beautiful?
0:23:45 > 0:23:47Do you know what time it is?
0:23:47 > 0:23:49Right, enough dangling out of this world-famous building,
0:23:49 > 0:23:51I've got a job to do.
0:23:51 > 0:23:53First, we have to turn the lights off.
0:23:53 > 0:23:55This takes place just after 10pm
0:23:55 > 0:23:58and it allows the team to change the time without anyone outside noticing.
0:24:00 > 0:24:03- Here we go, west is going off. - Yeah, west.
0:24:03 > 0:24:05- South.- Yeah.
0:24:05 > 0:24:07That's done, you've switched off the lights.
0:24:07 > 0:24:09- And we can now set the clock. - Yes, we can.- Amazing.
0:24:09 > 0:24:12Now, with Ian's help we need to stop the mighty Big Ben from ringing.
0:24:12 > 0:24:13BELL RINGS
0:24:13 > 0:24:16This is the fantastic piece of equipment that we have to use.
0:24:16 > 0:24:18- Yeah, I reckon I can work out where this goes.- Yeah.
0:24:18 > 0:24:20- Until it's nice and tight.- Yeah.
0:24:21 > 0:24:23- Now, that's not going anywhere. - Nope, that's it.
0:24:23 > 0:24:26That's barred off now, it's not going to make a noise.
0:24:26 > 0:24:29With Big Ben silenced we can get on with changing the time.
0:24:29 > 0:24:32Unlike a clock at home that you simply wind back one hour,
0:24:32 > 0:24:34this mechanism can only go forwards,
0:24:34 > 0:24:37so Paul has to move it on to exactly midnight,
0:24:37 > 0:24:39where it will be held until real time catches up.
0:24:42 > 0:24:44- Are you ready?- Yeah, ready.
0:24:46 > 0:24:49So, what's actually happening on the outside of the clock face now
0:24:49 > 0:24:52is in complete darkness you'll just see the silhouette
0:24:52 > 0:24:53of the hands moving round.
0:24:55 > 0:24:58Time flies when you're having fun, eh?
0:24:58 > 0:25:01Three, slow it down a bit. Two...
0:25:01 > 0:25:03Bang on, there you have it. Midnight.
0:25:04 > 0:25:07Midnight is chosen to allow for several hours of maintenance work
0:25:07 > 0:25:11to take place. And one of the most important jobs, winding the clock.
0:25:11 > 0:25:12There we go.
0:25:12 > 0:25:15Years ago, my grandma used to have a watch and it used to have
0:25:15 > 0:25:17a little wheel on the side you would wind up and that would give
0:25:17 > 0:25:20the watch energy, it would give it power, so it would keep working.
0:25:20 > 0:25:23This doesn't have batteries in it, which means we effectively
0:25:23 > 0:25:25- have to wind this up, don't we?- We do.
0:25:25 > 0:25:27OK, before we start, how many of these have I got to do?
0:25:27 > 0:25:30You've got to do 120 to make it last three days.
0:25:30 > 0:25:32Quite a work out, isn't it?
0:25:32 > 0:25:33Bit more sweat.
0:25:33 > 0:25:34Harder.
0:25:36 > 0:25:38That's it. Excellent.
0:25:38 > 0:25:41'Phwoar. I never thought this would be so tiring.'
0:25:41 > 0:25:43Although the clock starts running from midnight,
0:25:43 > 0:25:47it isn't until 2am that everything is switched back on.
0:25:47 > 0:25:50And then Big Ben can do its thing once more.
0:25:50 > 0:25:52Now, you know me and you know that I love gadgets.
0:25:52 > 0:25:55This is probably the oldest gadget I've ever seen
0:25:55 > 0:25:59and it is by far my favourite. Look at it. Isn't it beautiful?
0:25:59 > 0:26:01Ladies and gentlemen, boys and girls, that is Big Ben.
0:26:01 > 0:26:04So, the clock face has now been turned back on
0:26:04 > 0:26:07and we're now going to head over to Big Ben himself, herself,
0:26:07 > 0:26:10and we're going to find out if what we've done downstairs has worked.
0:26:10 > 0:26:13We've literally got a few seconds left before these dongs,
0:26:13 > 0:26:16so I better get these on.
0:26:16 > 0:26:20All right, here we go. Three, two, one...
0:26:20 > 0:26:24BELL STRIKES
0:26:24 > 0:26:26DONG!
0:26:26 > 0:26:29Ho-ho. So, there you have it. Now you know why it's called Big Ben.
0:26:29 > 0:26:32Not because it's big, but because it's huge and sounds amazing.
0:26:32 > 0:26:33I want one.
0:26:33 > 0:26:37DONG!
0:26:37 > 0:26:39Join in every Thursday on CBBC.