Hydrogen Alpha - Sixty Symbols

so today we're on the roof of the physics building at the University of Nottingham in a rare moment of English sunshine to talk about some of the light that comes from the Sun so this is one of our to teaching telescopes that we have here at the University of Nottingham but this is a special one this is a solar telescope so it's designed to look at the Sun not your usual telescope where you take it out at night it's actually a daytime telescope I mean yeah come on in well everyone knows that you never look at the Sun with your naked eye and you especially never ever look at the Sun through binoculars or a telescope the one exception being this kind of telescope which is a solar telescope this telescope allows only a certain wavelength of light from the Sun through and this is a wavelength of light I want to talk about today this is hydrogen alpha what we call h alpha in astronomy and this is a very specific way of length of light it's 650 6.28 nanometers and it marks the transition of electrons around the hydrogen atom from the third level to the second level so if you think of the atom as this classic of Borat and we've got nucleus and you've got electrons orbiting at fixed energy levels around that nucleus transitions from electron falling from the third level to the second level when they do that they release an amount of energy and that energy radiates at that specific wavelength and we call that hydrogen-alpha it's the first level in the Balmer series which is all of these different transitions that come down to that N equals 2 energy level well if we're thinking about the Sun in particular if we look at the Sun using an H alpha enabled telescope it allows us to peer into what's called the chromosphere literally the color sphere of the Sun which is one of the levels of the atmosphere of the Sun by narrowing down the light that you allow through your telescope till just this one interesting transition is seen that's where you get the beautiful detailed pictures of the Sun with the surface features the sunspots the big prominences and filaments and you wouldn't normally see that because the detail is just washed out I'll give you an example so in astronomy we often put filters in our telescope something like this that will restrict the wavelength range of the light that's allowed in this is a very crude filter it's really only allowing sort of reddish light in but we want even more specific light to come through we want not just a weight range of say a hundred nanometers to come through we want say only one nanometer around that specific wavelength to get down to our telescope so we can see that detail as it's set up now we can't look through this telescope because it's got a camera on the end of it unfortunately when we turned it on today that camera wasn't working yeah it is possible to fit an eyepiece to it and you can look through it and the only reason again for safety's sake that you can look through it is because it's got really heavy-duty filters in it this is a blocking filter that reduces the amount of light and the wavelength of light otherwise you would you would fry your optics and you would fry your eye if you looked through an eyepiece on it this camera over here is connected to this computer that does all the image acquisition this isn't a lot of picture this is not unfortunate live picture because the cameras not working today but this is a picture that's been taken previously with this telescope what you can see is the chromosphere of the Sun and you can see some of the details some of these light filamentary features these dark sunspots and this beautiful big loopy prominence as well as some more fuzz around it around the side all I can see is a smiley face a smaller ah I'm sorry it's like the Sun smiling at me it is like the Sun smiling at you but the Sun is just one star and I'm not a solar astronomer when I deal with stars they're in units of hundreds of billions and they're wrapped up in packages called galaxies so here at Nottingham along with some colleagues of mine we have used another telescope a much bigger telescope a 10 meter diameter telescope on the island of la palma called the grand telescope Jochen arias or kamme we were awarded 90 hours on the telescope spread out over a period of a few years do a very large project with an instrument on the telescope that works in a way not unlike the filter on this telescope works this is not entirely correct analogy because the telescope is different this is a refracting telescope it has a lens and not a mirror but it has a very special thing inside here which is called a fabry-perot etholon it's an interference filter and its job is to vastly restrict the amount of light coming in to isolate exactly the wavelengths that we want so it turns our wide filter into a filter with a width of just a nanometer or so and it's tunable so it's got two little plates inside a reflecting material and the light comes in bounces off those plates back and forth and forms interferences so constructive interference where the wavelength match the phase of the wave length of light matches and builds up the amplitude and destructive interference where it cancels out and that allows only specific wavelengths of light to get through this system the blocking filter takes care of the rest and out the other end comes only our wavelength of interest H alpha H alpha in extra galactic or galactic terms tells us where stars are forming in the galaxies and that's one of the really fundamental characteristics that we're really interested in in understanding how galaxies form and how they evolve so if you think of something like the Orion Nebula the big star forming region in the belt near the belt of Orion that's an emission nebula so that's lots of gas and inside that stars are forming and the stars that form are really hot really young stars they're radiating lots of UV light ultraviolet light there ionizing all of this gas around it so they're stripping the electrons from their hydrogen atom and then when those electrons fall back down they ran out radiation including this really important hydrogen alpha so hydrogen alpha when we look at a galaxy is a marker for where stars are forming and we measure that in terms of solar masses per year we measure a star formation rate of a galaxy and some galaxies are forming stars in a much more vigorous rate than others and part of our job is to figure out why that is why that why not just a lot from the stars themselves well we do that as well that's another so we try to approach this problem from as many angles as we can and directly measuring the ultraviolet light from young stars is one direct measure of the star formation rate and we do that using ultraviolet telescopes but to be very effective we have to get above the earth the atmosphere to do that because thankfully the atmosphere shields most of that UV radiation from from getting down to us so that's one tool in our toolbox h-alpha is very handy it's in the visible regime which is you know where our optical telescopes you know our flagship telescopes are built to operate and it gives us another direct measurement it's not the whole story because some of that star formation can be hidden it can be enshrouded in by dust and in that case the UV photons don't make it out they get the heat up the dust but we can still see that because you can't hide that radiation it just comes out reradiating at longer wavelengths say in the submillimetre and you need another different kind of telescope to look look at that but you put all these measurements together and you get a complete census of the star formation in a galaxy and then when we put them all together we get this cube that lets us do some really interesting things because it not only gives us a picture of a galaxy but it gives us a go to hoe only I can get it into the middle of that stack and you find where the peak of that spectrum is that's what that galaxy looks like in each alpha

Channel: Sixty Symbols

Views: 197,141

Rating: 4.966691 out of 5

Keywords: sixtysymbols, H-alpha, Hydrogen (Chemical Element), Astronomy (Field Of Study), sun

Id: CH880_VrxxU

Length: 8min 31sec (511 seconds)

Published: Thu Sep 03 2015