Full transcript
0:00hi-oh this week we're looking at chapter
0:02five from your textbook and really it's
0:04all about light and the different ways
0:06we study light because we're gonna see
0:08an astronomy light is incredibly
0:09important also though you're gonna have
0:13a few surprises I think this chapter
0:15because you might be used to the idea of
0:16light I mean you experience it every day
0:18well at least most people do and thing
0:21is though it's quite a bit more
0:23complicated than it might first appear
0:25for one thing there's many different
0:27forms of light we're gonna see and also
0:29it has some incredibly strange
0:31properties so why is it that we might
0:34need to study light well the thing is in
0:37astronomy everything's really really
0:39really far away even if we look at the
0:41Andromeda galaxy which is a really
0:43nearby galaxy in our terms here it's
0:47quite close by that being said quite
0:51close by still means this two point five
0:53million light years away now that means
0:56we're probably never going to go there
0:59unfortunates probably inaccessible to us
1:01even if we looked at the new who new
1:04Horizons mission that ship it would take
1:08about 450 billion years to get there
1:12traveling at its current speed 450
1:15billion years and sure maybe we'll get a
1:18lot faster but still we're not likely
1:20gonna be travelling to any other
1:22galaxies probably ever to be frank but
1:26even if we somehow did get there the
1:29thing is any information we got would
1:31take 2.5 million years to get back here
1:35because it's 2.5 million light years so
1:38the signal we send back would take 2.5
1:40million years to get back to us so
1:43starts giving you an idea of the
1:45difficulties we face in astronomy we
1:47can't just go and visit these things so
1:50what we have to do is study the light
1:53and see what we can learn from that and
1:57again that's what this chapter is all
1:58about because I mean sure that was one
2:01galaxy but most galaxies are much
2:04further than that
2:05even so ok 450 billion years to get to
2:10that one
2:10imagine the ones even further
2:12because some of them are much much much
2:14much much further and so again we study
2:17the light or the electromagnetic
2:19radiation given off by these objects and
2:23we'll define that right now
2:25electromagnetic radiation well let's
2:27start off with the radiation part
2:29radiation got this definition here it's
2:32the idea of transferring energy I mean
2:34you might be used to the energy
2:36transferring in a wire to charge your
2:38phone well this is when we're actually
2:42transmitting energy for one space to
2:44another without physical connection so
2:46without a wire say connecting them so
2:50energy transferring from one spot to
2:52another even though there isn't a
2:54physical connection between those two
2:56spots great so what is electromagnetic
2:59radiation then well that's when we have
3:04electric and magnetic fields
3:07waves oscillating and transferring that
3:10energy so we have electric and magnetic
3:12fields that are transmitting energy from
3:15one point to another without a physical
3:17connection between them and one example
3:19of electromagnetic waves or
3:21electromagnetic radiation would use that
3:24term really interchangeably
3:25electromagnetic wave electromagnetic
3:26radiation well one example is left good
3:31old everyday light you take light from
3:33the Sun that is electromagnetic
3:34radiation what we're gonna see
3:37light is only one tiny example we also
3:41have radio waves we have UV rays when we
3:45were tanning the microwave you use all
3:48these things rely on electromagnetic
3:50radiation and so does your cell phone
3:51but again what you have is these
3:54perpendicular electric and magnetic
3:56field lines these waves that are
3:58oscillating into space so much like this
4:01image shows it's these propagating
4:03electric and magnetic waves that are
4:05transferring energy from one point to
4:07another without a physical connection
4:10between them we're going to talk more
4:11about waves in great detail but first
4:14let's talk a little bit more about
4:16electricity and magnetism and really
4:20we're thinking Maxwell for a lot of this
4:22information because he did a lot of
4:24experiments and saw that electric
4:26city and magnetism were very very highly
4:30related and you might be used to you
4:32again electricity the currents in the
4:34wires powering your house magnetism
4:36you're probably mostly used to the
4:38magnets you use to stick something to
4:39your fridge or the bar magnets well it
4:42turns out those concepts are incredibly
4:44intertwined because what we find is that
4:48if you have a magnetic field and really
4:51a magnetic field is you can imagine if
4:54you have a magnet a magnetic field is
4:56being exerted by this on any object
4:58nearby so it's these imaginary lines
5:01spreading out from our magnet that would
5:03exert a magnetic force on objects so
5:06similar to the idea of gravity we can
5:08define a gravitational field around any
5:11mass that would influence the other
5:14masses nearby so magnetic field is
5:17produced by say a magnet if you have a
5:20magnet it has a magnetic field around it
5:22and when we change that magnetic field
5:24say moving the magnet when we do that it
5:29produces an electric current so if you
5:32take a magnet and actually that's pros
5:34reasons you don't want to put like a
5:35magnet near your computer because it can
5:39induce an electric current you can
5:42actually hurt your electronics so you
5:45might have heard about the idea that you
5:46can take a magnet and use it to ruin a
5:48drive well yeah because it will induce
5:50electric currents so you have to be
5:54careful but we also find that if you
5:57have an electric current that's changing
6:00it can produce a magnetic field so there
6:03can be a slight magnetic field produced
6:05around the wires in fact that's why if
6:09you've ever say plus installed a TV you
6:12might see those magnetic couplers that
6:14are supposed to help dampen that
6:16magnetic field it produces um if you
6:18haven't seen it don't worry but the idea
6:20is that an electric current the changing
6:22electric current can produce a magnetic
6:24field so very related interchangeable
6:26ideas in a way so what does that mean
6:29well I'm gonna go back as a crass I'd if
6:33you had this changing magnetic field in
6:35this changing electric field oscillating
6:37through space they can help propagate
6:39each other
6:40that's why this continues on and we'll
6:43talk more about that in a sec but
6:45another important idea is that if we
6:49have a charged particle a charged
6:52particle so something in the Sun like if
6:57it's oscillating if it's moving it's
7:00vibrating what we can find is that will
7:03produce that electromagnetic wave and
7:05again as I just said then those electric
7:07and magnetic components spreading out
7:09from that charged particle are gonna
7:11help keep propagating each other so if
7:14we have a charged particle something say
7:17in the Sun that's vibrating it will
7:19produce an electromagnetic wave which as
7:22we alluded to really is light so that
7:30means we have all these distant objects
7:32and what we're gonna see that the idea
7:35of a vibrating charge is very very very
7:38very common so all these different
7:40objects these galaxies far away these
7:42stars they are producing electromagnetic
7:47waves so very distant objects produce
7:50these electromagnetic waves they
7:51propagate through space and eventually
7:54reach us and we can study them and we
7:57can learn them and what's very important
8:00is that these electromagnetic waves can
8:03actually travel through empty space
8:05which is really good because there's a
8:07lot of empty space between us and most
8:08these objects even between us and the
8:10Sun remembers an astronomical unit worth
8:13of distance between us quite a bit of
8:15space and all of the electromagnetic
8:18radiation the light travels through
8:20space and comes to us and by studying
8:23that light studying those
8:25electromagnetic waves we learn about
8:28these very very distant objects that we
8:30can't travel to if we can still learn
8:33about