so today we're on the roof of the
physics building at the university of
nottingham in a rare moment of english
sunshine
uh to talk about
some of the light that comes from the
sun so this is one of our two 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 all right you can take me in
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
accession 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 the 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
wavelength of light it's
656.28 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
classical bore atom where you'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 two 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 sun spots 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 a range of say 100 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
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 at it this camera over here is
connected to this computer that does all
the image acquisition so this isn't a
live picture this is not unfortunately
live picture because the camera's 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 around the side all i can
see is a smiley face a smile
i'm sorry it's like the sun's smiling at
me it is like the sun smiling
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 telescopio
canarius or grand canyon we were awarded
90 hours on the telescope spread out
over a period of a few years to 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 a 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
etalon 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
wavelengths match the phase of the
wavelength 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 they're 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 rain 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 at a much
more vigorous rate than others and part
of our job is to figure out why that is
why that why not just the light from the
stars themselves well we do that as well
that's another so we
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's 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 they heat up
the dust but we can still see that
because you can't hide that radiation it
just comes out re-radiated at longer
wavelengths say in the submillimeter 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
only i can get it to the middle of that
stack
and you find
where the peak of that spectrum is
that's what that galaxy looks like in h
alpha