>> Jonathan Fay: Welcome everybody. I'd like to welcome Doctor Jeffrey Hall to this I
Microsoft Research talks series. Since June of 2010 Doctor Jeffrey Hall has served as a director
of the Lowell Observatory in Flagstaff Arizona where Pluto, the dwarf planet was discovered.
He joined the staff of Lowell in 1992 as a postdoc research fellow and received his bachelors in
physics in 1986 from Johns Hopkins University and a PhD in astronomy and astrophysics in 1991
from Penn State. His research at Lowell has focused on solar and stellar activity cycles with the
goal of lending and astronomical perspective to solar influences on terrestrial climate. He
presently serves as a member of the Northern Arizona leadership alliance and is a former
president of the governing board of Northland Preparatory Academy College Prep High School
as well as Board of Directors of the Flagstaff Symphony. His principal application is music and
he has been a substitute organist in the Episcopal Church of Epiphany in Flagstaff for nearly 23
years. Please give a welcome to doctor Jeffrey Hall. [applause].
>> Jeffrey Hall: Thank you. All right. Thanks a lot. It's really a pleasure to be here with you
today. I'm visiting the Seattle area from Flagstaff, a place where I have really enjoyed living the
past 23 years, along with our staff member Lisa actors from Lowell.1:36. We are a private
nonprofit research institution. We have a number of supporters and friends who are members
of our advisory board here in the Seattle area. We are just in the area for a couple of days
making some visits and we got to know Curtis Wong here at Microsoft Research through
conversations about the WorldWide Telescope and when he heard we were coming up here he
said would you like to come give a talk over at Microsoft and I said I would love to give a talk at
Microsoft. So here we are. Lowell Observatory is first and foremost a research institution. We
were founded in 1894 by Percival Lowell. He was interested in observing what he thought was
evidence of intelligent life, the famous canals on Mars. And since our earliest beginnings we
have grown to be an institution that operates a campus on Mars Hill just west of Flagstaff. And
our research facilities have moved off-site to two separate dark sky sites, and most recently
we've opened up a brand new four meter telescope that cost us a cool $53 million. And I'll
come back to what we can do with that right at the very end. These days as the director of the
observatory I spend a little more time it seems on budget spreadsheets and administration then
doing science, but I am an astronomer by training and so I thought I would spend the bulk of
the day today talking about the research project that I have been involved with at Lowell for 23
years, ever since I came there in 1992. It's a program that is uniquely suited to the kind of thing
that we are really good at which are projects that take a long time to unfold and that require a
lot of observing time. Since we own all of our own facilities, we are uniquely set up to do these
kinds of things to look for patterns in nature that don't unfold on the time scale of say a threeyear grant cycle but you need a little bit more time to uncover what's going on. So we'll go
ahead and talk about the variations of the sun and stars like the sun and how that all connects
to the topic of climate change. I was born and raised on the East Coast, did all my schooling
back there. I didn't move to Arizona until I was 27, and one of the joys of living in the
Southwest are just these extraordinary vistas. If you have seen Forrest Gump or perhaps driven
this road, this will look familiar. Principally this picture is proof that I am crazy enough to stand
in the middle of a road in the interest of getting an iconic picture, but this is just up north of
Monument Valley just north of the Arizona border in an area that was inhabited back in the
1200s by a people locally referred to as the Anasazi, the old ones. They are remnants of their
habitations all over this area that we call the Colorado Plateau. One of those habitations is not
very far from Lowell Observatory in Flagstaff. This is only about 30 miles out of Flagstaff at
Wupatki National Monument, so we're Flagstaff is a cool ponderosa pine forests, you don't
have to go far out and far down to get into a rather spectacular open desert setting. This was in
2012 and it was on the day of the annular eclipse and the park service invited us out to the
Pueblo for a talk about eclipses. So I went out there and gave a talk right here. This is the old
community room at the Pueblo where they would gather for whatever oral history they were
recounting and it was an incredible environment to give a talk about the universe. The park
superintendent told me they had more people there that day then probably ever in history.
There were about 1500 people. And sort of to stand there and talk about a eclipses in the ruins
of this Pueblo where probably 1000 years ago a people long gone did exactly the same thing
was really a neat thing to do. As you can see, it's just ruins. The whole area of the Colorado
Plateau was abandoned by the Anasazi between about 1270 and 1300. The archaeology books
that I've looked at say that there was possibly a little bit of strife and fracturing society, but the
tree ring records of the time also indicate there was a protracted three-year drought in the
period that no doubt would have stressed the environment severely and quite possibly
contributed to the abandonment of the area. Given what Arizona is normally like, three
decades of drought could be a pretty severe thing indeed. So there's an example there on time
scales of decades very near where I live now of significant climatic changes coming and going.
So we'll just file that away and come back to it a little bit later. 2012, Flagstaff doesn't always
look like this. Sometimes Flagstaff looks like this. This was 2010 which was the last really
strong El Niño year. We've been hearing about El Niño lately. What it tends to do is create a
higher probability of wet winters in the Southwest due to the impact on the location of the jet
stream. This was late January of 2010. It was unquestionably in El Niño link event. We had a
series of three storms come through that dropped about four feet of snow in Flagstaff and out
where our four meter Discovery telescope is we had about six feet of snow and that was when
we authorized the purchase of a bobcat because we just couldn't plow that stuff to actually lift
it out of the way. So severe snowstorms are certainly known to strike and not just in 2010, but
there was a whole spate of them in the late 1880s. This is New York City after the great blizzard
of 1888 back in a time when civil services were much less equipped to deal with this kind of
thing. And this was part of a series of extremely harsh winters in the 1880s that hit the United
States. You'll find that recounted in the history textbooks as well is in popular literature. The
late James Mischner used this in a couple of his novels describing the harsh conditions in the
upper mid West where trees were literally exploding as they froze in the night. There were
massive cattle die offs and so forth. This was another period, the 1880s of unusually, cold
severe winters in the United States. Going back into time a little farther, this is Louis the
fourteenth, one of the longest reigning of French kings, 1643 to 1715. Sometimes he was called
a sun king. And there is a very interesting connection here. A period of about 70 years of very
long severe winters in Europe stretching almost perfectly coincident with the reign of Louis the
fourteenth. Short growing seasons, heightened crop failures, famine, a very difficult time, we
will see the significance of this in just a minute. As an interesting aside, I mentioned my
interest in music which has been long-standing, there has been some discussion in the
literature. This was the era when the Stradivari family and the Guarneri family were building
the violins that now sell for $20-$30 million apiece. I had the privilege of hearing Rachel Barton
Pine just a couple months ago playing the Brahms Concerto on one of the Guarneri violins that
Brahms himself picked out for that concerto. It was kind of cool to hear. There's been some
theorizing that the unusual climate affected the tree growth patterns in Europe at the time and
created would with a slightly different density and characteristic that leads to the extraordinary
sound of those particular instruments. Just a little interesting aside. Here we have evidence
shown in three different slides of different types of undeniable climatic shifts all within fairly
recent history, 30 years in Arizona of drought, a decade of severe winters in the United States.
Now seven decades, these unusual periods can persist for a very long time. What might be the
reason here? Let's switch from climate anomalies and talk about our nearest star and having
gone back in time let's go forward through time and survey a couple of the things that we've
learned about the sun and how it's activity changes. Sunspots, the well-known phenomenon on
the surface of the sun, had been observed for millennia. There are occasional naked eye
sightings of sunspots going way back into the records from the Orient, but they're very spotty
because it's not really easy to observe the sun directly. 1610 which is about the time of the
invention of the telescope began the first series of really systematic observations beginning
with Galileo and his contemporaries. And one of the first things he noticed was the spots
weren't always in the same place, but from day to day they would move across the surface of
the sun. And Galileo reached the brilliant intuitive notion that the spots were associated with
the sun and that the sun rotates. As you may know this got him into a whole lot of trouble with
the religious authorities of the day for suggesting that not only was the sun not perfect and
stationary but it had these ugly black blemishes on it. But nevertheless Galileo derived a
rotation period for the sun remarkably close to what it actually is. He was a fairly sharp guy. So
1610, so what you do if you are aware that sunspots exist? You count them. And people ever
since 1610 have been tracking how many sunspots there are. So let's look at the evolution of
that record. By 1845 a German astronomer named Heinrich Schlabach made the observation
that there was a periodicity, that on the timescales of about 11 years the number of spots
would rise fall, rise fall, rise fall. I guess I do have a pointer. By 1900, you might ask, here we
are 1845, we are about two centuries after the first observations of Galileo. Why in the world
did it take so long? I mean this looks pretty obvious, so why did it take so long for that to come
out? There are basically two reasons. Number one, this was slightly before the invention of the
internet, so we didn't have quite the level of information exchange that we have today. People
were keeping records in more isolated areas. But beyond that, here's 1610 and the first
observations from Galileo, but then look here. There is a period when basically there were no
sunspots at all into the seventeenth century. So after nearly a century, if you were an observer
of sunspots, you would never have the remotest idea that there was any kind of cycle going on.
So it was really only until up in here that it really started to become obvious that there was a
cyclic pattern. Now, remember Louis the fourteenth. This is about 1645, 1715. This coincides
precisely with the period of unusual, severe weather in Europe, Siberia, the United States. So
here you have a very interesting compelling set of circumstantial evidence for an apparent
cessation of the solar cycle creating a substantial climatic impact here on earth. And this, by
the way, is an astronomer in England named E Walter Maunder and his name will come back
shortly. And then to complete the tour of our understanding of the sun, this is a fellow named
Charles Greeley Abbot who lived to an admirable age. He died in the 1970s at 102 or
something but he spent virtually his entire career trying to observe what he thought were not
just changes in spots, but changes in the entire brightness of the sun. Astronomers throughout
the twentieth century were interested in measuring how much energy are we really getting
from the sun. What is what we called the solar constant, because the assumption was that the
sun was constant. And if you look at it from day to day, it certainly has that appearance. It's
this nice bright light that looks pretty steady. Abbot was using the best equipment available to
him of the day to try to see if the sun actually was not constant. Maybe it various. He came to
the conclusion that it was. This is an example of getting the right answer for the wrong reason.
He didn't have the equipment that can detect the solar variability we know today, but he was
convinced that there were solar effects on climate and that the sun varied. His work led him to
tempting vacation spots like Algeria here and this is nothing if not a study in perseverance and
dedication for the duration of a career. But he did conclude something that we have then been
asking ourselves ever since. Let's look at what the sun, our variable star actually looks like in
different guises. This is a white light picture of the sun. It looks reasonably featureless except
for the spots. You see these prominent spot groups. For reasons we can go into in the Q&A, if
you like, they tend to come in pairs. They tend to be a little bit angled, tilted like that and they
appear in both hemispheres. In between it doesn't seem like there's much going on. But today
we have instruments with the capability of observing stars in particular areas of the spectrum,
and when we look at the sun and other spectral regimes or specific spectral regimes, we get a
very, very different picture. For example, in the light of the hydrogen atom, the sun is mostly
made of hydrogen, a very interesting and dynamic surface appears. You see dark areas that are
associated with spots, but then these very bright areas, features hanging up in the atmosphere.
There's little pillars and loops off the lem. There are these dark features running here that we
call filaments and these basically, these are these except instead of looking across them now
we are looking down them and so they are looking dark. So these features are all over the sun.
You can see a little more clearly in the light of the calcium atom. You can definitely see the
spots, but suddenly we see around the spots are all of these areas of denser, hotter plasma that
we call plage, and these are areas of increased energy and increased emission that accompany
all of the sunspots. And finally, now that we're in the space-age, we can send spacecraft above
the atmosphere and observe the sun in wavelengths inaccessible from the ground, so the
ultraviolet, the x-ray, all of that radiation that fortunately doesn't reach the ground in great
quantities. And when we look in the sun in the light of the iron atom, it looks very different.
I'm going to show you two images of the sun in the light of iron. This is in the far ultraviolet, 17
nanometer light. And this is taken near the minimum of the sunspot cycle. So when the sun is
relatively quiescent and you can see that there are a couple of active areas. See these beautiful
like loops of material over here? But otherwise it's mottled. It's clear there are some striations
in there, but overall, fairly quiescent. However, just a couple of years later near activity
maximum, it looks like this. So now you can see clearly that there are active latitudes. Look at
the size of that loop. On this scale the earth would be a little bit bigger than the laser pointer
dot. It would be, but not a lot bigger. So this loop is considerably larger than the Earth. These
are right here as well. If you could superimpose the white light image, you would see sunspots
at the base of this loop. That's why they tend to come up in pairs. There's a region. You see
spots here, spots here, spots here. So this is the active Sun and you can see that the sun is
wildly different as it goes from its activity minimum to its maximum. This lent some credence
to the fact. What is climate? Climate is the thermal environment of Earth's atmosphere. The
fundamental driver of that environment is the sun. We have this interesting possible relation
with solar activity and climate. And finally, 1978 we began to answer the question rigorously
that Abbot could not answer with his equipment. This is a little satellite called Nimba 7. It was
launched in January 1978 and it was the first of a series of satellites that had aboard it an
instrument that simply looks at the sun and measures its total brightness, whether it's optical
light, infrared, ultraviolet, the integrated brightness of the sun and how much energy is hitting
Earth. The reason you want to do this from above the atmosphere and the reason that Abbot
couldn't reach the conclusion he wanted to reach was the interference. If you go out on a night
and you see twinkle twinkle little star. Astronomers hate twinkle. It might be kind of a
romantic image of a star, but what you're getting is that nice pencil beam of light from the star
that has made its 60 trillion mile trek across the universe to earth and in the last 50 passes
through Earth's atmosphere and the turbulent motions of the atmosphere start reflecting it and
refracting it and so you get this and if you see stars like Sirius in The Big Dog low in the
atmosphere and you'll see it flashing green and that's the colors being refracted in the Earth's
atmosphere so that every now and then it almost appears to change color on you. And that
was the effect that made it impossible from the ground. Even today, almost impossible to try
to do those kinds of measurements, you need to try to do them from above the atmosphere.
This was the first satellite to do it. Since then there have been a string of satellites that have
continued that record and they show incontrovertibly that as the solar activity rises and falls
the entire sun gets brighter and fainter. So it's total energy output rises as it gets more active.
Actually, what I will do is backup a couple of slides and explain how that works. The basic idea
is as the sun gets more and more active there are more spots, so there are the spots. And spots
are dark, so it would seem like more activity would make it fainter. And the reason the spots
looked dark is that they are cooler than the surroundings. The visible surface of the sun is only
10,000 degrees Fahrenheit or so. The spots are may be 7 to 8000. So they look darker than the
surroundings, but then look around the spots. There's all this bright stuff that comes with the
spots. And the going idea is that there's this two component model that as the sun gets more
active you get the spots darkening and all of the associated regions making it brighter and the
bright regions win. So there's an offset but the bright regions more than offset the dark ones,
so it gets brighter as it gets more active. So the fact that the solar energy changes as its activity
changes led this fellow, Jack Eddy, who published a wonderful paper in 1976, in which he called
attention, so this was published in Science. If you Google, sorry Bing Jack Eddy Science 1976
you might find this paper. It's totally readable. It's wonderful. He calls out this period of solar
cre-essence and coined the term Maunder Minimum after E. Walter Maunder who was the first
astronomer who first noticed it. He presented the entire sunspot record, one of the great
achievements of modern observational science. You can see what happened here. The cycles
kind of went away. This period is very well documented. There were not many spots, very few
reports of solar aurori, which in that time which solar activity causes. Then it comes back into
gear, but you can see that there are lots of patterns beyond just 11 years. There's this, sort of
an 80 to 100 year pattern. Let your eye trace the peaks of the cycles which we now call the
Glysberg cycle. There's even a general overall tendency for steadily increasing amplitudes of
the cycles, so the sun is clearly doing things on timescales much longer than 11 years, longer
than 100, and in all probability, longer than even 400 or 500, but we haven't had the window to
observe them. That's one of the real things we struggle with, I think, in doing science is
scientists trying to be rational and objective and logical and yet we're looking at these grand
patterns with our 70 or 80 year window onto the universe or whatever we are blessed to get.
Yet there are things that operate on such grander timescales. You might notice some
interesting things in here we can discuss a little bit at the end. Here, you may have read about
the year without a summer. It was right here. Now in this case, it was probably a volcano. It
was probably a volcanic eruption and not the sun. Here's the 1880s. That's probably more
volcanoes. We'll get back to that, but there are reasons for things to change other than the
sun. Nevertheless, these interesting correlations remain. Here are the modern solar cycles.
This is the sunspot number from 1960 up to about the present. One thing you will notice is
here's a strong cycle, slightly weaker one in the seventies, stronger, stronger and now weaker
and now the current cycle that started in 2010 is one of the weakest on record. It's actually a
very sedate cycle and there have been studies published in the literature starting in about 2006
that predict that the next cycle might be almost nonexistent. There's interesting evidence that
we may be transitioning out of a period of strong cycles and back into possibly even another
grand minimum akin to the one of 400 years ago. If that were to happen it would be extremely
interesting. We learn a lot from nature when it does something unusual, because it lets us
explore the boundaries of the parameter space. To see another solar minimum would be very
interesting to observe. We have to be extremely careful with this kind of science, however. As
we have learned, there is a really compelling correlation between the Maunder Minimum and
climate and possibly between other periods of solar cre-essence and climate. For example, you
can trace the solar activity record back beyond 1610 and try to reconstruct the sunspot
behavior. You can't do it with telescopes because they had been invented yet, but you can do it
with tree rings and you can do it with ice scores and isotope records. And when we go back and
reconstruct one thing we find is there appears to have been another little solar shutdown
between guess when? 1270 and 1300, precisely corresponding to the Anasazi abandonment of
the Colorado Plateau. Now, you wouldn't publish that as a formal claim in a scientific paper.
It's a correlation. Here's a really strong correlation that persisted for about 20 years back in the
second half of the twentieth century, the number of sunspots. Here's two full solar cycles going
up and down and up here you'll see these little elephants. This is another striking correlation.
There is a striking anti-correlation with the number of Democrats in the Senate. This is a
slightly absurd example, but there are plenty of papers in the literature back in the early part of
the twentieth century comparing solar activity to things like commodities prices, which if you
are talking about climate effects maybe, but the stock market? So the road to ruin is littered
with the bones of a lot of people who have looked a little too hard for things that maybe
weren't there. Can we do? If we want to understand, yes or?
>>: I don't know if you want questions are not.
>> Jeffrey Hall: Yes, anytime.
>>: You're talking about the brightening and dimming. How much is the brightening and
dimming?
>> Jeffrey Hall: It's about one part in 1000, so one tenth of one percent. It's below of what
Abbott could have measured. Yes?
>>: You mentioned 1270 to 1700. Is that a little Ice Age?
>> Jeffrey Hall: Yeah. Let's just talk about that for a bit. The little Ice Age is a climatic period
the goes from about 1300 to about 1700. It was a period of generally cooler weather, not
globally. It's spatially complicated. And there were severe episodes and lulls. And some of the
severe episodes appear to be associated with some of these sensations in solar behavior. The
severe winters of the Maunder Minimum were one of the severest and last episodes and after
the end of the Maunder Minimum, we seem to be coming out of what was called the LIA.
>> Jonathan Fay: Just to let the people online know that they can post an online question and
repeat that over the mic so they will know.
>> Jeffrey Hall: Right, we are broadcasting to millions here.
>> Jonathan Fay: But let them know that they can use the interactive tool to post the
questions.
>> Jeffrey Hall: Okay. The point there is the listeners online can post an interactive question at
any time and we will be happy to answer that as well. The problem if we want to understand
the behavior of the sun and one of the fundamental questions that has been asked when we try
to understand modern climate is what was the sun like during the Maunder Minimum. If the
sun gets brighter and fainter as the activity rises and falls, what if the activity shuts off for 70
years? What happens? Does the sun get, sort of just start dimming and the solar energy hitting
Earth goes way down and possibly explain a cooling of climate in certain areas? What is the sun
like? What was its brightness behavior like? The problem is we didn't have a whole lot of
satellites in orbit in 1645, so there's not much you can do. Or is there? Every night there's this
beautiful laboratory that goes by overhead. And you've got lots and lots of stars, many of them
are very dissimilar to the sun. The stars in Orion, you would not want to put any of those down
where the sun is or we would be crisped rather rapidly. But there are lots of humble little stars
up there that are fairly similar to the sun. Since about 1960 there have been two very longrunning programs. One is ours and another is that Mount Wilson Observatory. They were set
up to observe the behavior of a whole ensemble of stars to use them as test particles for what
the sun might be like on long-time scales. The analogy I like to use when I go to elementary
school classes is suppose your teacher asks you to write a report about people and you don't
know anything about it, but you try to write a report by observing one person. If you just
observe one person you're going to have a really skewed view. You want people of both
genders, all ages, all races and you want to understand people. So using the stars we can try to
get a much more informed picture on our own sun. This is been going on for about 50 years
now at Mount Wilson Observatory using the hundred inch telescope and two telescopes at
Lowell, one of our rather older ones and a somewhat newer one. This is the one I've been
using. These are telescopes set up as we'll see in a minute to observe the activity cycles, like
the sunspot cycles. The question in 1960 was we didn't even know. Do other stars have cycles
or is the sun just a complete weirdo? It was possible it might be. And then these telescopes
are robots. They are completely robotic. We program them at the start of the night and they
just observe all my and then e-mail you the data. It's wonderful because you don't have to pull
an all nighter to get the data. These observe the brightness changes. So what we been trying
to do all these decades this measure the spot cycles, measured the brightness changes and see
what they do. Here's a brief history of these programs. This is Mount Wilson Observatory, the
pristine dark skies of Los Angeles California. This was a program initiated by a gentleman
named Olen Wilson, purely coincidental relative to the name of the Observatory. In 1966 he
set up an instrument and started observing a set of about 100 stars, just over and over again,
night after night, month after month, year after year using the 100 inch telescope. The reason
he could do this is because Mount Wilson is an institution very much like Lowell. It owns all of
its own telescopes. It's not a competitive peer review process to get a one-week slice of time
on the instrument which is say like Peak Observatory, some of the competitive facilities work.
Even if your proposal was successful, you couldn't do this kind of project because you can't get
the telescope time. So Wilson patiently observed for about 12 years and found three
overarching types of behaviors in the stars. You can see the inventive, romantic names that we
give to our stars. HD1835 is a fairly young star and it varies a lot. There is nothing really
identifiable there. These are the irregular ones. HD81809, look here, here's a nice well
identified up and down, about two thirds.
>>: This is 10 years?
>> Jeffrey Hall: Yes. This is 1967 to 1978 roughly. Sorry my axes are pretty small. And then
about 15 percent of them up here, absolutely flat. And so the question is, aha, is this a modernday analog of the Maunder Minimum and if so, can we now observe stars like this and transfer
the results to what the sun does? So the fundamental question that Wilson was able to answer
is yes, stars have activity cycles just like the sun, and yes, some stars appear not to have any
activity cycles for a long time. So we kind of see the ensemble of two behaviors that we see in
the sun and then this turns out to be a very young star. The younger the star is the more erratic
it is. Stars are like people, I think, in that regard. As they get older they kind of slowdown. Our
program is a compliment to the Mount Wilson program which is no longer running. It ceased in
2003. This is the 42 inch telescope. Before I switched from scientist to administrator, I spent
many a night out there from dusk to dawn. This is a 42 inch telescope, meaning the mirror is
about one point one meters in diameter and we do essentially the same thing that Wilson did
except where Wilson observed a very broad swath of stars, different types, different
characteristics, we have really focused our program very tightly on the most solar like stars we
can possibly find. We want to observe suns, because you don't have to get very different from
the sun to have a totally different kind of star. Our program differs from the Mount Wilson
program in that this is Lowell Observatory's smallest telescope. This is our solar telescope. It's
a fiber-optic that points at the sun, sees it as an unresolved disk, so we can pipe starlight into
our spectrograph from the telescope through a fiber and sunlight through this fiber and
observe the stars and the sun with exactly the same instrument. That's not a trivial thing to do
because the sun is many billions of times brighter, apparently, then the stars. So if you try to
observe the sun with your telescope, you'll rapidly melt everything downstream. So this is a
way of skinning that cat. Here are some of the major research observatories, on Hawaii I was
giving a talk at one of the astronomical conferences and they had their results. They were
bragging about their results that they had published 40 papers per square meter of aperture. I
couldn't resist pointing out we have published many trillions of papers per square meter of
aperture. I think some people thought that was funnier than others, actually. So what do we
do? The problem with observing activity cycles of the stars is we can't take a picture of a star
and see a spot. They are too far away. So all of those stars, or nearly all of them are point
sources. We can't take an image. We can't count spots like we do on the sun, so imaging is out
of the question. What we can do is to take their spectrum, which is like the star's fingerprint.
When you look at the spectrum of a star you'll see that it is shot through with all of these dark
lines, the absorption lines. Each one of those lines is caused by a particular element in a
particular atomic state. These two really dark ones are caused by calcium and you will
recognize there's the calcium image of the sun. That's the sun; this is the spectrum of the sun
here. This one down here is a star that's a little bit cooler and fainter than the sun and it's got
lots and lots of lines. And the calcium lines are not as distinct. There are tons of iron lines in
here. And then finally one of the hottest stars we observed, this is Altair in Aquila the Eagle. I
just done a graphic there putting it relatively to scale to show you how big it would probably be
compared to the sun and that's what it's spectrum looks like. The take away here, every
spectrum is a little bit different. It's literally like a fingerprint. With the spectrum you can tell
how fast the star's rotating, if it's moving towards you or away from you through the Doppler
shift of the spectral lines, its composition through the strength of relative lines caused by
different elements. And finally, these calcium lines, since the star gets brighter as he gets more
active, at the bottom of these calcium lines you see little spikes of bright emission and you
measure those, and as the star gets more active, that goes up and then it goes down. So you
can create these plots that are proxies for spots, flares and activity in the stars. You can graph
about stellar activity cycles using the spectrum even though the star itself is just a dot. There is
our instrument. This is a slightly vintage instrument at this point. It dates to about 1990, but I'll
just show you the basic optical train of how these things work. The fiber comes in here and the
light first hits this beam splitter and it goes in here and write there you can see a diffraction
grating and this is where the calcium like gets into the camera. That diffraction grating is using
kind of the same principle as if you hold up a compact disc obliquely and you see colors coming
off of the surface. That on this side is another type of dispersing system that collects a different
part of the spectrum, so we get a large swath of the spectral lines. There's the grating and then
there's the mother of all prisms right in here that splits up the light and is putting it on our
detectors. The detectors we use are the detectors of choice in astronomy today which are CDs,
so exactly what you've got in your phone. They were just coming into use in astronomy when I
got into the field in the early 1990s and revolutionized how astronomy is done.
>>: Why do you use both the grating and a prism for the same spectrum?
>> Jeffrey Hall: Yeah, that's really an excellent question. The reason for that is we want to
observe the stars at pretty high resolution. This is a special type of grating called in a shell and
so it gives you high resolution but as a result of that a lot of the orders of diffraction get stacked
on top of one another and so the prism is a cross disperser and it's actually really beautiful for a
CCD because you have all of these stacked orders and the cross disperser gives you a rectangle
of orders, so you get the whole thing on one little chip. I'll give you just a couple of case
studies. This is the start 18 Scorpii and all I'm showing you here is a plot of its activity. This is
the light going up and down in those calcium lines. This star is a fairly modest little fellow. If
you go out and look at Scorpius in the summer, you can just barely see it at the edge of naked
eye vision. It's a dead ringer for the sun, as close as we can find. It's got a cycle that is maybe
seven years long, so considerably shorter than the sun's. There is an example of a star very
similar to the sun but with remarkably different characteristics, at least as far as the length of
its activity cycle goes. Here's a young one, Epsilon Eridani, which has a planet around it, by the
way, very fast, a three-year cycle. Here's one that's almost close to a Rosetta Stone of what we
are looking for and I really wish we had a few more years of data on it. Look here. Nothing
going on and then pow. It starts going into a pretty vigorous for your cycle, but there's nothing
there. Question, is this an example of a star that did what the sun did 400 years ago? It wasn't
cycling and then when it was. To be really confident of it I would really like to have three or
more your years of a flat tail to demonstrate, but otherwise it really looks like it did what the
sun did in 1715, because if you see the cycles are gradually, it's like it's coming out and then
getting itself ramped up. Yeah?
>>: Is it your hope that the cycles will be faster with a star that only cycles every four years
versus 11?
>> Jeffrey Hall: That certainly helps not having to wait 11 years to confirm that it's actually a
cycle. The length of the cycle may have to do with the rotation rate of the star. There's a lot of
relationships between how fast the star is rotating and the characteristics of the activity and
the cycle, because rotation is one of the things that generate it. And then if you take our
program and Mount Wilson's I just love long series like this. Combined series of two stars that
we both observed. We pick out things that would be impossible to get on a short program.
Here's a star that has a primary cycle, we pick back up, so we are expecting another one out
here that's about 17 years, but then superimposed is this really fast two year one and then it
kind of settles down. There's this little gap where Mount Wilson wasn't observing it. It comes
back up and settles down and then starts back up. So you see the same behavior getting
recovered. There is actually a little bit of something like this going on in the sun. There's the 11
year cycle and then there's a little lower amplitude two-year thing. So putting all this together,
where do we end up? We can ask a couple of questions. From what we've been able to
observe as we observe the activity of the stars and then we observe their brightness, do stars
get significantly fainter when the cycle turns up? What are the climatic implications of the cycle
turning off? Here's where science gets really, this is why I like working in science. These are
plots of the stars from the Mount Wilson program and from ours. Mount Wilson, the Mount
Wilson data suggested those are cycling stars and those are non-cycling stars. So when I start
turns off its cycle, it slides into a really low state of activity and thereby you infer that it might
become significantly fainter. If a star becomes significantly fainter, then there are implications
for how much solar forcing you might plug into climate change models since the 1700s. We
couldn't recover the result, so we are using stars much more like the sun and we were using
close to 60 stars in this study, 57. And this is based on 13, so you've got statistical weight
coming in and here in the blue, these are our cycling stars. The red were our non-cycling stars
and the yellow is the sun, so we've got the sun as well and we couldn't find any statistical
difference in the samples. So our initial conclusion was that the Maunder Minimum sun was
probably like the modern sun except without the cycle and it wasn't really sinking into a very,
very deep minimum, granting that there were significant effects on climate. At least from what
we have now, we think when stars, when the cycle seems to turn off it sort of just is ceasing
and not really changing its basal magnetic state until it gets going again. Does the sun affect
climate? Yeah?
>>: I'm sorry. On the previous graphs you said that the red is the stars that were not cycling.
Those are the stars that you saw cycling and then are just the measurement of the flat or these
are the ones that you never saw cycle?
>> Jeffrey Hall: Right. These were the flat ones. We've got that one star where we think we
may have seen a transition, but that's only one. What we really need to observe are more
transitions. But this is the set of stars where we look at them and it's like if you looked at the
maunder minimum and you happen to catch that section, just like that.
>>: But you don't know whether when it goes from cycling to flat maybe it's different for
starters that are just always flat?
>> Jeffrey Hall: Maybe it is, that's right. That's going to be a next step here at the end. Does
the sun affect climate? It does. This is from a paper I think published around 2001 or 2002.
Just to demonstrate the differences in global temperature between a solar maximum and a
solar minimum, so measure the temperature of the earth spatially resolved at solar max, solar
min and color code it. The red areas are warmer. The blue areas are a little bit colder. So a
solar max is a little bit warmer out here, a little bit warmer in Seattle, Western U.S. Eastern U.S.
tends to be a little bit colder. We are talking a tenth of a degree here. It's not profound but it's
measurable. You can see it. It does, and here there is a pretty significant affect in Siberia. So
even though the overall variation's pretty small, if that were to cease for not a year before
rising up for 70 years, you can imagine that there could be significant climatic effects. Since
1700 we think of climate change or global warming has kind of a modern-day problem or issue.
Earth has actually been warming since the end of the Maunder Minimum in 1700. And here's
how that kind of stacks up from another paper published in nearly 2000s. Here's the 400 year
sunspot record again. And here was the best conclusion from the folks who tried to do the
climate reconstruction. To do a climate reconstruction you look at all the variables, you plug in
the changes in the atmosphere, the circulation patterns in the atmosphere, you use solar
forcing. So how much has a sun changed over the last 400 years? And that's kind of where we
plug in. I'm not a climatologist, but from an astronomical side, we're trying to say the stars
indicate the sun has may be changed this much since it came out of a grand minimum, not this
much. So when you do that you can put together an irradiance reconstruction for the solar
brightness and the conclusion here was that after 1700 this solid dark line is temperature, right
here. It is slowly rising after the 1700s and then there is a little down and then it starts coming
up. And then if you continue this it would continue on up until about here, so it's going up
rapidly at this point. And then the reconstructed solar brightness tracking it reasonably well
until very recently. So mostly solar forcing. Solar activity does influence climate and it does
influence global temperatures, albeit in a spatially complicated way. Then notice right here,
mostly volcanic forcing, so in the nineteenth century there were some very large volcanic
eruptions, Tambora, in the early 1800s. Krakatoa, in the 1880s right, that period of severe
winters. You can see a brief dip in the record in 1991 after Pinatubo went off. And what's
going on there is volcanoes are throwing large clouds of aerosols into the upper atmosphere
which tend to lower the temperature because they reflect sunlight, but the difference between
aerosols and carbon dioxide is aerosols precipitate out quickly, whereas, carbon dioxide and
methane and other greenhouse gases stick around for a long time. Evidence from the
twentieth century and particularly from the last 40 years, the continuing,, the generally
strengthening solar cycles up to the 1970s probably contributed to some of it, but the best
guidance is 25 to 30 percent of modern warming in the last four decades or so can be
attributed to solar forcing. The most of it must be due to anthropogenic or man-made effects.
So that's kind of the suite of things since the end of the Maunder Minimum and the stellar
guidance from the long-term observing programs is that recently the sun is not the principal
contributor. So now where are we going from here? It's a very interesting time, as I alluded
before. We had long Maunder Minimum. This has come to be called the Dalton minimum. It
was a period of some really weak cycles and then it came back up. We had a period of very
strong cycles in the twentieth century and now it's really settling down and people are
hypothesizing that we might be headed into another period like this one. Is that going to
happen for sure? I don't know. But the people who are arguing this are measuring the strength
of the sun's magnetic fields right around the sunspots and finding that they are rather weak.
Using that to project a very low sunspot cycle, sunspot number for the next solar cycle. So I
think everybody kind of pooh-poohed this idea when it was first floated in 2006, but there has
been increasing acceptance of the idea that we might be transitioning into another period of
solar cre-essence. One other thing sort of arguing in favor of this is the folks who look at solar
activity on really long timescales have done some analyses of when there is a period of strong
cycles, how long do they usually last? And they based that on the ice core records and the
isotope records. It seems to be typically about 80 to 100 years before the things change. This is
kind of where we are. If the current set of strong cycles started around 1920, we are coming up
to that. So it's an interesting time to be in the field and the thing to do now is coming back to a
question from before, we need to observe transitions and we need to observe stars that are
really like the sun. And the problem is that once you narrow down the parameter space that
much, you don't have a big sample, so you have to go to fainter stars and we can't go to fainter
stars because they take too long to observe. So like Roy Scheider in Jaws, we're going to need a
bigger telescope. And so there's yours truly here. There's some folks from Northern Arizona
University and this is Lowell's new telescope. It's called the Discovery Channel Telescope, so
you may be able to infer where we got a capital gift to help fund it. Otherwise, it was entirely
built with private funds. It has opened up a tremendous new era of opportunity for Lowell. But
one of the things we can do with it is reachable much fainter stars then we have before. Now
what we want to do is go from the studies I've been talking about today to more focused
studies of the small-scale magnetic fields on stars that are not cycling and try to understand
how they are different from the cycling ones to provide some guidance on what might happen
in the future should the sun actually go into a minimum. So stay tuned. Before the sun makes
any of us any sort of latter-day Anasazi we'd like to understand what is going on in the future
and it has been a really interesting project to be part of and we'll keep you posted. So it's
getting close to an hour. I definitely want to leave time for a little bit of Q&A if we have time
for some. All right. So I'll stop there and be happy to take any questions. Thank you very
much. [applause].
>>: The ice ages, can you do any correlation with the ice ages like from 10,000 years ago and
back?
>> Jeffrey Hall: Yeah. I always like to point out in a talk like this is that we are living in an Ice
Age. We happen to be in an interglacial, but where there is freestanding ice on the Earth's
poles. So now we are talking about phenomena that play out over long 40,000, you know, long
timescales and have been linked to slow changes in the Earth's orbit, so-called Malankevich
cycles. So these are effects that are playing out on somewhat faster timescales and the ice
ages. During the dinosaur, the era of the dinosaurs, which was not an Ice Age, all of the
continents kind of gathered in one big blob and oceans circulating around the poles. Now we're
in a phase where you got Antarctica, a landmass sitting at the South Pole which allows a lot of
freestanding ice to collect. And the Arctic Ocean is kind of hemmed off by North America and
Asia, so we're kind of in a configuration now where an Ice Age can exist. I think that Earth has
only been in an Ice Age for a smallish fraction of its existence. Right now within an Ice Age, so
there are advances and retreats and we're kind of in a retreat right now.
>>: Do they correlate at all with the sunspots cycles?
>> Jeffrey Hall: No. First, we can't…
>>: How would you know?
>> Jeffrey Hall: Right. We can't trace it that far.
>>: Could you say a word about current events? How do they correlate with sunspots and so
on?
>> Jeffrey Hall: That's a function of the solar activity cycle. But it's not directly tied with climate
connections.
>>: Do they appear at the peaks of activity or do they get stronger?
>> Jeffrey Hall: Not necessarily, no. There's more activity, more violent, more eruptive events
in the sun's atmosphere at an activity maximum, for sure. Yes?
>>: Do we know why sunspots even happen and why is there even a cycle?
>> Jeffrey Hall: We know the basics of that, yeah. The cycle is a combination of the sun's
rotation, so it's tied to the rotation, and the turbulent motion of the convective material below
the sun's surface. Since the magnetic field is a property of the matter in the sun, as the sun
rotates the magnetic field kind of gets twisted up. The sun is not a solid body, so the equator
rotates roughly once every 25 days and the pole once every 33 days. As it rotates there's this
twisting of the magnetic field that is then given a torsional component by the convective
motion and that produces what is effectively a magnetic dynamo. And that's what's producing
some of these looked like features you see. And so the solar cycle is the gradual ramping up as
that geometry gets steadily more complex followed by a settling down as the active regions
reconnect and diffuse and are recycled into the solar interior. The bulk nature of the cycle is
well understood. The full calculation has been beyond the reach of even modern computers.
The full details are not understood, let alone why it would appear to cease. One thing we can
tell, when the sunspots disappeared for 70 years, there is still ample evidence in the isotope
record that variations were going on. The dynamo was still operating, but it was just at a much
reduced level, at least macroscopically. So something was still going on and continues, but we
don't understand what would cause it to settle down and then ramp back into gear. There was
another question.
>>: How did you identify the, how did you decide on the list of sun like stars that you are going
to observe?
>> Jeffrey Hall: We are limited by the size of our telescope to stars of a certain magnitude, so
we go down to about eighth visual magnitude, which is maybe 60 times or so fainter than you
can see with the unaided eye. So what you do is you use stars that are measured to have
properties as near as possible to the sun. Every star has what we call a color, which is sort of
the difference in brightness in two different parts of the spectrum. So you look at stars that
have exactly the same color. They might be chemically similar as you can determine from the
spectrum, similar rotation rate. To the extent that you can determine a star's mass, which is
very difficult to do, so you just look for the nearest stars to the sun within that parameter
space. There just are not that many. When you are limited to really bright stars by your
instrumentation, you're limited down to a pretty small sample. By going to a much bigger
aperture, then we suddenly have a much larger sample to pick from, and we've got lots of stars
known to have planets and those would be really interesting to observe.
>>: What percentage of stars would that be?
>> Jeffrey Hall: Down to magnitude 8, 9, there are some stars that have been identified at eight
and nine that are even better than the one in Scorpius as dead ringers for the sun, so a handful
of them. If we could get to magnitude 11, you would have many 10s probably, so you would
have a much better sample to pick and choose from. And then what you would want to do is
design an observational program that would get you some more understanding quickly because
you don't want to spend another 50 years or 70. I'll be sick of this project by the time I'm 130,
so we want to find a way to infer what's going on a little more quickly than just sitting around
for 70 years and saying that's really not cycling. It's still not cycling.
>>: Are there any data mining opportunities from projects like DIAH [phonetic] that are doing,
you know, many different observations, albeit they're doing it for astrometry, but they are
getting some [indiscernible] data.
>> Jeffrey Hall: There are, yeah absolutely, like say from Kepler. You can definitely use the
Kepler observations. In fact, I've got a collaborator down in Tucson and we've got a little
project going, or will have a project going next year, to observe some of the Kepler stars. So
yeah, for sure. And then from the Kepler data you also can identify which stars have planet
candidates and a number of those are quite sun like, so you can go start hitting them. The
problem is we can't do those stars with our current facility because they are too faint. But if we
can get a spectrograph that covers the right spectral features and we can go to those stars and
make some observations, it would get some interesting results pretty quickly on how they
differ. You can use a really neat inference. You can observe the current stars. We've got stars
that we know are cycling and stars that we know don't, so observe them in this new way and
see what they're doing and then observe some of the fainter ones and, you know, infer…These
do this if they are cycling and not, so maybe these are doing this and infer which ones are
actually in a quiet state and then you don't have to observe them for 10 or 12 or 15 years.
>>: When I was at your observatory I took a visit there and I saw this little dinky telescope and
they were showing the sun off of it. And I had a chance to look through that and it was sort of a
slinky sort of effect as the sun went across itself. Can you explain to us maybe what that is? It
kind of looked like you would watch the sun and it looked like a wave rolling across the front of
it.
>> Jeffrey Hall: That might just have been turbulence in the atmosphere. What you are
probably using there, it looked orange, right?
>>: Yeah, it was a little tiny scope, Coronado?
>> Jeffrey Hall: Coronado, yeah, so that's the solar telescope and it's equipped with a hydrogen
alpha filter and so that's exactly what I was showing you before, the hydrogen image of the sun.
And so often what you see there is you'll see motion and that's kind of like seeing the twinkle,
as you're seeing turbulence in the atmosphere that's creating this apparent motion on the
surface of the sun. Sometimes you actually see features evolving. You can see a flare and 15 or
20 minutes it will be different because they really do evolve on that kind of timescale. Yeah?
>>: How do you calibrate long-term brightness measurements?
>> Jeffrey Hall: Okay. Good question. Those photometric telescopes that are observing the
brightness of these stars, we observe them in quartets. And so you observe a program star and
then three stars that you kind of select for being completely dead, so their brightness isn't
varying and you do a differential between them rather than an absolute, because that's really
hard to do. And so what we typically do is we'll observe four of them and look at the
differences between all of them and then pick the two that are the flattest and then we'll
referenced the program stars to those. But what'll happen every now and then is one of your
program stars will be going along and then suddenly it decides and it's like oh man. You want
to make a star variable just pick it as a comp star and that'll guarantee that it'll start doing
something weird. So it's all differential photometry. It can actually be done very, very
accurately. We have to get down to milli-magnitude to make that work. That's a great
question.
>> Jonathan Fay: I have an online question. What is the approximate max distance from our
solar system of these eighth magnitude sun like stars, e.g. 100 parsecs, 1000 parsecs?
>> Jeffrey Hall: Very good question. The sun if it were 10 parsecs away, it would be about fifth
magnitude, so the stars we are looking at like 18 Scorpii is like 40 parsecs. So we're going up to
like 50 or 60 parsecs away when we're doing a star with solar luminosity. So that is 180 to 200
light-years, which in the grand scale of the cosmos we aren't even getting off our front porch.
So these are nearby stars. If we start doing the stars that Kepler is looking at, then you are
starting to get a little farther out. You're getting 500, 600, 800 light-years. Still, that's just the
local part of the galaxy. Galaxy is a big place. Yeah?
>>: Do the number of planets, the size of the planets, the orbital distances, do they detect solar
or stellar dynamic?
>> Jeffrey Hall: Great question. The answer is yes. We have observed some stars where there
are planets so close to them that the planet's magnetic field is interacting with the magnetic
field of the star. That doesn't happen with our sun because the planets are more spread out.
But when we first started finding XO planets, astronomy will always surprise you and the first
XO planet we found was totally not expected. It was just one of these hot Jupiters, a Jupiter
like planet, but really close to its star. The prevailing wisdom was solar systems would kind of
look like ours, with the small dense rocky ones having kind of formed near in and the big light
gas bags formed farther out, but here was a totally different thing. And now we have found
some of these stars that, in fact, do interact with the magnetic field and vice versa. These are
planets that have orbital periods of three days or something.
>>: Does the amount of fusion that goes on in a star stay pretty steady?
>> Jeffrey Hall: Reasonably steady for a healthy star like the Sun. The sun is using something
like 600 million tons of hydrogen to helium in its core per second. As the sun ages on the main
sequence it will gradually become more luminous. As it gets old and start using other elements
in its core then things start to become increasingly unstable and the timescales become
increasingly short. But the overall energy output of the sun is quite stable and as long as its
mass isn't changing that much you're going to have a relatively well-defined rate of fusion.
Yeah?
>>: You said from the spectrum you can tell how quickly a star is rotating. How does that
work?
>> Jeffrey Hall: Because you can tell that if there is a spectral line and the start is rotating, then
this part of the star is coming towards you and that part of the spectral line gets blue shifted a
little bit and this part of the star is going away. So as the star rotates more rapidly the line gets
broader and you measured the broadening. There will be a natural thickness to the line if the
star is not rotating at all and then you can measure the broadening. So that really actually gets
to be a mess if you have a very rapidly rotating star the lines are all thick and kind of blurred
together and it can actually be kind of difficult to determine what the actual rotation rate is.
Anything else?
>> Jonathan Fay: Let's thank the speaker. [applause].