The Daniel K Inouye Solar Telescope is the largest solar telescope ever built. With a
whopping four meter diameter mirror, it reveals the Sun at the highest resolution ever attained.
It's currently finishing up construction and commissioning atop the 10,000 foot summit
of Haleakalā, Hawaii. When it commences science operations in 2022. DKIST will be capable
of examining the Sun in unprecedented detail from its surface, all the way out to its corona,
and it joins NASA's Parker Solar Probe and ESA's Solar Orbiter just in time to catch
the Sun waking up from a decade long quiet period.
Welcome to Launch Pad, I'm Christian ready, your friendly neighborhood astronomer. And
there's a new big player on the solar telescope front. The Daniel K Inouye Solar Telescope,
or DKIST as the cool kids call it, is very much under construction, but even its early
first light images reveal the Sun's surface at a level of detail never seen before. Despite
being stuck here on Earth, DKIST's resolution is higher than ESA's Solar Orbiter, which
gets to within 1/3 Earth's distance from the Sun.
So today we're going to talk about how the world's largest [solar] telescope works, and
what it can tell us about our home star. But first, I'd like to thank Magellan TV who are
very kindly sponsoring today's video. Their documentary called "Set Course for the Heart
of the Sun" tells the story of the Parker Solar Probe, which flies so close to the Sun
it actually passes through its atmosphere! You can enjoy this and many other documentaries
on Magellan TV. It's a new streaming service that features topics on art, nature, history,
and of course space and science. And now Magellan TV is offering my viewers 30% off an annual
subscription. That's a full year of Magellan for just 350 a month and this offer applies
to both new and returning subscribers alike. Simply visit the link in the description of
this video to claim your discounted membership today.
The Sun's explosive behavior is driven by magnetic activity. Solar flares and corona
mass ejections can actually damage satellites, disrupt communication networks, and knock
out electrical grids. So being able to predict solar storms well in advance means understanding
the details of how the Sun's magnetic field works. And that means monitoring small scale
changes on the Sun to see how they develop over time. Much of the Sun's extreme activity
takes place in its outer atmosphere, called the corona.
Yeah, I've heard the joke before. Corona...good one... Even though it's high above the Sun
surface, the temperature is actually millions of degrees hotter. And that doesn't make any
sense. It's like raising your hand away from a hot stove and then it suddenly heats up
and burst into flames. So understanding how the Sun's internal energy gets transported
into the corona is one of the biggest questions we have about the Sun, and by extension about
stars in general. One idea is that energy gets carried via twisted filaments called
magnetic flux tubes. Of course, the sun's magnetic field is invisible, but it traps
charged particles just like a bar magnet traps iron filings. And not only that, but the magnetic
field polarizes the light that's emitted by those trapped particles. The stronger the
magnetic field, the greater the polarization. DKIST is designed to take images, spectra,
and polarimetry of the Sun all at the same time, and it can do it at a high enough cadence
to actually watch the magnetic field change.
The observatory is named after Daniel K. Inouye, the late senator from Hawaii. It's 4 meter
primary mirror collects more than six times as much light as the previous record holder.
It might seem a little strange to need such a large mirror to study the Sun. I mean, after
all, it's so bright you can even see it during the daytime. So what do we need a large mirror
for? Well, the bigger the mirror, the higher the resolution and therefore the smaller structures
it can see. The magnetic flux tubes are thought to be less than 100 kilometres across.
With a four meter mirror, DKIST can resolve features as small as 25 kilometers, so it
should be able to spot them without much difficulty. A large mirror makes the telescope a lot more
sensitive to light. Now that sounds really strange given that they're looking at the
Sun. Yes, the Sun is very bright, but the Sun's corona is very faint and it can only
be seen by artificially blocking the Sun's disc. The bigger the mirror, the more photons
it can collect to make out those fine coronal details.
More photons, collected quickly means more light for the cameras, which means short exposure
times, and that allows DKIST to image the Sun once every five seconds and build up a
near real time view. Instead of a traditional telescope design. DKIST uses an off axis Gregorian
optical design to eliminate any central obstruction that would otherwise scatter light, and this
is especially important for observing the corona.
The primary mirror is only 75 millimeters thick and it's polished to an accuracy of
less than two nanometers. In other words, if the mirror were scaled to the size of the
continental United States, its largest imperfection would be less than the thickness of a dime.
Since DKIST will observe the Sun all day long. It's mirror is supported by 120 actuators
behind it, and 24 additional actuators around its rim, These actuators push against the
thin mirror to prevent it from sagging as it moves throughout the day.
But looking at the Sun means that the mirror and the telescope gets very, very hot; hot
enough to damage the mirrors an render the telescope useless. So the primary mirror is
actively cooled from behind with chilled air. The mirror sends the beam off to the secondary,
but by this time the beam'ss diameter is shrunk from 4 meters to less than 1 meter, and that
means about 13 kilowatts of energy is bearing down on the secondary. Tat's enough to pop
a bag of popcorn in about 3 seconds.
So to protect the secondary from melting down, the light has to first pass through a heat
stop. The heat stop is a donut shaped pipe that's fed by large hoses that pump liquid
coolant through it. The coolant carries away something like 90% of the heat energy. Now
if the heat stop were to suddenly fail, an emergency shield closes to disperse the light
away from the secondary. But the shield can only do that for a few minutes before it disintegrates,
so during that time an emergency cover deploys over the primary mirror and the dome's aperture
door closes.
In fact, the entire dome is specifically designed to keep the telescope from overheating. It
does this with a combination of a white paint job, shielded shutters, and it uses a single
4 meter circular aperture door instead of the traditional open slit.
Now back inside the beam enters into the heart of the observatory, the Coudé lab. This is
where the science happens. The beam reaches the deformable mirror of the adaptive optics
system. 1600 actuators adjust the mirror surface 2000 times a second. This removes the atmospheric
distortions from the light in real time and allows the telescope to see features as small
as 25 kilometers across. The corrected beam can then be split.
To enter into multiple instruments, and this allows DKIST to image and take spectra of
the Sun at different wavelengths simultaneously. Different wavelengths of light correspond
to different layers of the Sun's atmosphere, so this technique allows a 3 dimensional picture
of the Sun to emerge in real time. The entire lab rotates to follow the Sun throughout the
day and keep everything lined up in the instruments. Its rotation system is so precise it maintains
the lab's position to an accuracy of just three ten thousandth of a degree. That's less
than the thickness of a human hair.
The entire lab is a clean room that keeps the dust levels down to just one part in 10,000.
Clean rooms typically you can do this by sealing off its doors, but the Coudé lab must let
the light beam enter through the roof. assing it through a glass window could introduce
more distortions and would require regular cleaning. So instead the Coudé lab uses an
air knife that blows a continuous blade of air across the roof opening. The airflow is
laminar flow, so there is no turbulence to distort the image.
Speaking of which, it's first light images are stunning and there a real teaser of what
DKIST will deliver. These are the highest resolution images ever taken of the Sun. It
reveals structures as small as 30 kilometres across. The image shows a pattern of turbulent
boiling gas that covers the entire Sun. These convection cells, called granules, are each
about the size of Texas. Hot solar plasma rises in the bright centers of the granules,
cools off and then sinks below the surface in the dark lanes along the edges. Now if
you look along some of these dark lanes, you'll see that there are some tiny bright markers
of magnetic fields. These bright specks are thought to channel energy into the corona.
In other words, they may be the long sought magnetic flux tubes that heat the corona.
Now this image was just meant as a test of the telescopes camera and optical system.
It's not science quality, so nobody can draw any proper conclusions about what the bright
spots actually are. But it covers an area of 36,500 by 36,500 kilometres of real estate.
Yet it reveals details as small as 30 kilometres across. That's actually about a factor of
10 smaller than ESA's Solar orbiter will be able to see, even though it will close to
within 0.3 astronomical units.
However, Solar Orbiter is also carrying a number of different instruments on board,
including in situ experiments that can only be carried out near the Sun.
And it canmage the Sun at ultraviolet wavelengths and will eventually climb above the plane
of Earth's orbit and give us our first glimpses of the Sun's poles.
And then nothing will come closer to the Sun than Parker Solar probe, which will fly through
the Sun's corona at just 0.05 astronomical units. And then there's the Solar Dynamics
Observatory, SOHO and many others with their own unique capabilities. It's like they're
The Avengers of Heliophysics. In any event, the timing for all of this is actually pretty
great, because the Sun is starting to become active again. That means we're going to start
seeing more sunspots, flares, and corona mass ejections as the Sun's magnetic field starts
to tangle up. In fact one of DKIST's early images was of this sunspot, taken in January
2020. It really shows off the three dimensional structure of the sun spot, the dark central
region is where the magnetic field lines are so densely concentrated that they can open
up a huge gap in the surrounding convection cells. And by huge I mean about the size of
the continental United States.
But believe it or not, that's actually not really that huge for a sunspot. Many are actually
the size of Earth and some can grow to be even much, much larger.
Now that the Sun is starting to get active again, we can watch the sunspots evolve in
very fine detail, and this is going to help answer some long held questions about our
home star, not the least of which is why is its corona so hot? In fact, the Parker Solar
probe is getting closer to the Sun with each orbit, and it will eventually get so close
it will fly through the Sun's corona. But it's already made some surprising discoveries
about the Sun's magnetic field, and even translated some of its measurements into sound, I made
a video about that, so I'll tell you more about that and let you listen into those sounds
of the Sun in our next video. Thanks to my patrons for their generous support. An I'd
like to welcome Pete back and Geeta and Todd Vandermark. And if you'd like to join me on
this journey through this incredible universe of ours, will please make sure you subscribe
and ring that notification Bell so that you don't miss out on any new videos. Until next
time, stay curious my friends.