Full transcript
0:00so I keep talking about how there's
0:02different types of light or more
0:04appropriately there's different types of
0:06electromagnetic waves where light is
0:10just one of them so this figure right
0:13here actually has a lot of information
0:15in it so we're going to take our time
0:16working through it
0:17but first things first it actually lists
0:19the different types of electromagnetic
0:21waves along the top and the different
0:23types of electromagnetic waves make up
0:26the electromagnetic spectrum the
0:28spectrum of all the different book types
0:30so we start off at the shorter waves all
0:33the way up to the longer waves and that
0:35means wavelength by the way shorter
0:37wavelengths to longer wavelengths
0:39remember a shorter wave would have a
0:42higher frequency and a higher energy
0:45whereas the longer waves would have
0:47lower frequency and a lower energy so
0:50starting at the very shortest ones we
0:53have gamma rays these are incredibly
0:55energetic waves and actually it would be
0:58very very detrimental to our health they
1:00would not support life they would be
1:03very very harmful then we have x-rays
1:06another high-energy type of wave and
1:09again this is something that's not
1:11exactly conducive for our health we use
1:13it to actually look at bones it can pass
1:16through our skin but not through bones
1:17so we use it image but there's a reason
1:19they're putting the lead shirts on you
1:21when you're getting an x-ray because we
1:23don't want to expose ourselves to a lot
1:25of x-rays then we get into the
1:27ultraviolet range which again pretty
1:29high energy and can be a little
1:32detrimental they can cause our sunburns
1:34they can cause skins cancer so we have
1:37to be a little careful with ultraviolet
1:39and then we're finding into the visible
1:41light visible light which is what we're
1:44used to the light we can see the rosy
1:48boob of the rainbow those are the colors
1:50making up the visible part of the
1:52spectrum after that on to the longer end
1:55we have infrared things that are used
1:58often in security cameras because well
2:01see later why that one might be but
2:03that's where they might be used
2:05microwaves after that which are still
2:07longer than infrared and are actually
2:09quite literally used in your microwave
2:11to help cook
2:13and finally into radio waves which are
2:15used to when you listen to your radio
2:17probably on the drive in so we also can
2:22look at this image and see this you can
2:26see it talks about the atmosphere and we
2:27have all these weird bars underneath the
2:29different types of wavelengths well what
2:32this is showing is how far into our
2:34atmosphere they actually pass and you
2:37can see we have the higher areas of the
2:39atmosphere down to our troposphere where
2:42we experience our weather and where you
2:45can see down to the ground where we are
2:47well you can see the different
2:50wavelengths only pierced certain
2:51distances when we're looking at camera
2:54rays thankfully they don't make it
2:55through our atmosphere down to us which
2:57is really good because as I said they be
3:00incredibly harmful to us they would kill
3:03us life wouldn't exist on this planet if
3:05gamma rays were passing into our planet
3:09x-rays are also blocked ultraviolet you
3:13can see is mostly blocked but part of
3:15the ultraviolent band does get down to
3:18us that's why we always have to be a
3:20little careful to avoid this UV light
3:23that can be harmful to us visible does
3:27pass and you can see it makes it all the
3:29way down to the ground this is the
3:31so-called optical window where we can
3:34see and that allows us to actually look
3:37all the light from distant stars distant
3:39objects will pass all the way to the
3:42ground so if we want to study it we can
3:44from the ground where as x-rays gamma
3:46rays we'd have to study it from higher
3:48up but visible light makes it to the
3:52ground and this is actually why we see
3:54visible light why humanity is evolved to
3:59see visible light or see later that our
4:01Sun happens to be brightest in the
4:03visible spectrum also that light makes
4:06it to the surface so we evolved to be
4:08able to see visible light because that
4:10was the most common light that was
4:11coming to us from the Sun see infrared
4:16mostly gets blocked again a little bit
4:18gets in microwave also a lot of it is
4:21blocked and then radio waves this is a
4:23huge part of the spectrum there
4:25large and part of it makes it down to so
4:28there's a radio window where we can also
4:30do and look at radio waves from the
4:33earth so this allows us to study certain
4:36types of objects objects giving off
4:38visible light and radio light or later
4:42radio electromagnetic waves here on
4:44earth whereas the other ones again we
4:46might actually have to do them either
4:47from high up in the atmosphere or from
4:49space so a lot of good information in
4:52here about the electromagnetic spectrum
4:55there's also a table in your book and
4:57you just a little bit blurrier than I
4:59wanted so you might want to look at the
5:01book remember it is free so you can go
5:03in take a quick look at this figure it
5:05I'm not really gonna expect you to know
5:07the values here I'm not gonna expect you
5:10to know the wavelengths though I would
5:12expect you to know say that gamma rays
5:15are the shortest wavelength highest
5:17energy highest frequency microwave
5:19longest waves and we're talk more about
5:23this temperature thing in a set a little
5:24bit later some of these sources that
5:27would produce these different types of
5:29light some of them we won't be studying
5:31right away we'll see but one thing worth
5:36mentioning is if you look at the
5:38spectrum the ranges are not even from
5:41one part to another there is some of
5:44these ranges that are much much larger
5:46look at this one goes from 10 to 3 to 10
5:48to the 6
5:49where as visible is only a measly little
5:53300 nanometer range and nanometer by the
5:57way it just means times 10 to the
5:58negative 9 meters so it's a very small
6:03wavelength but this means the visible
6:07light is only a tiny fraction of the
6:10entire electromagnetic spectrum that
6:12last figure didn't really do it justice
6:14in fact if we look this is a more
6:16appropriate figure because it shows a
6:18logarithmic scale of the electromagnetic
6:22spectrum and a logarithmic scale means
6:24it jumps up by 10 every one of these
6:26factories is a factor of 10 bigger so
6:29this actually this one's more than a
6:32factor of 10 from here to here so
6:35just increases very quickly and our
6:37visible range is this tiny little bit
6:39right here when you look at the entire
6:42electromagnetic spectrum and this one's
6:44flipped from the last one gamma rays are
6:45on this side radar on that side you can
6:48see we represent a tiny tiny portion of
6:50electromagnetic spectrum so we only see
6:54a tiny bit of the total types of
6:57electromagnetic waves that are out there
7:00meaning when we study astronomy we have
7:02to study all of these ranges or we're
7:04missing an entire huge portion of the
7:07picture there's some objects we want to
7:09see don't radiate a visible light if we
7:12didn't study the other parts we would
7:14miss them so it's important to study all
7:16parts of electromagnetic spectrum to
7:19really get a true appreciation for
7:21what's out there in our universe and
7:23again we happen to only see a tiny
7:25portion of it our eyes are sensitive to
7:28see invisible light only so we when we
7:31do visible astronomy when we would just
7:33look at those objects that our eyes can
7:35see we miss a lot but we actually do
7:38look at all these different parts of the
7:40spectrum to get a full complete picture