- Good afternoon, everybody. I'm Katherine Blundell,
Gresham Professor of Astronomy. And the title of my talk this afternoon is, "Attentive Eyes." I'm going to be talking
about what we humans can see in the night sky
and what some of it means. So I'm going to be starting
with this beautiful picture taken through some
Australian eucalyptus trees by my friend and colleague Steven Lee. You can see right in the
center, a slender crescent Moon, the rest of the Moon being illuminated very, very faintly by Earth's shine. The crescent bit of the Moon of course is illuminated by the sun. What else can we see in this picture besides eucalyptus trees? Well, we can see Jupiter
up close near the Moon. And hiding in the trees,
we can see Mercury. It's a delight to study the
pattern and passage of planets through the night sky. And these are some delightful
examples, Mercury and Jupiter but I want to talk a little
more today about Mars. While this is a very
beautiful conjunction, conjunction meaning
the appearance together of particular planets in the night sky, I want to talk about Mars on it's own, what we can see and what we can
learn about the planet Mars, the famous red planet, the
fourth planet out from the sun. It's got a very thin atmosphere. But interestingly, days and seasons are very comparable to those of Earth because it's rotational axis and the orientation of that axis are very similar to those of planet Earth. A year on Mars is getting
on for twice that of Earth. So by astrophysical standards,
that's pretty comparable. So how do we go about looking at Mars and what can we actually see when we pointed telescope at it? Well, pointing a telescope at Mars is exactly what I did on Monday night, which those of you living
in the UK may recall, was a very humid night, we'd had a huge amount of
rain before the weekend. It's not at all easy observing something that's fairly low towards the horizon, so is looking through a lot of atmosphere above houses that are giving off heat and causing their own
turbulence and unsettlement to the atmosphere itself. So a standard technique, if
you want to look at Mars, is to take a whole movie,
a whole sequence of images and then pull out the best. This technique is formerly
known as Lucky Imaging. And so if I show you from
this entire movie sequence, some of the best ones, I hope you'll agree that they are distinctly better than some of the fuzzy ones we saw while the movie was
actually bobbing around. So this is a rather nice one. You can just about, I hope, get a sense of the slightly
different colored rock on the planet Mars. Slightly grayer towards the bottom left, slightly more muted apricot
towards the top right. In the bottom left corner, not that a planet has
corners I hasten to add, but at approximately the
eight o'clock position you can see some whiter light and that's actually
coming from the ice caps that are on the South Pole of Mars. Well, here's another still, taken from that blurry,
bouncy, bobbly movie, I was showing you earlier
and another one still. And I hope you get a sense
that these features on Mars are actually rotating as
we look throughout time. So these movies were
taken during the course, of perhaps, a couple of
hours on Monday evening and these are the best
ones that were pulled out. Now, an astronomer called Rob Tilsey has turned this into an art form and with an immense tour de force he has made 77 separate videos of Mars, 924,000 frames between them, and he's pulled out the
best 1300,000 or so. And he has been able to get an entire rotational period of Mars. And this shows you, I think, that you really can see these features propagating around on Mars, despite the limitations of observing during not tremendous weather from the UK. Now, the details of the
surface structure of Mars have been the source of some controversy and indeed confusion in past years, and the past century or two. So the Turkish astronomer, Antonaldi, who was a highly reputed observer, in many ways, a very skilled
empirical astronomer, for a while supported the
notion of canals on Mars. This was until he used a
larger, better telescope at the Meudon Observatory,
which is south of Paris and a telescope that has made
many important discoveries in the history of astronomy. The main proponent of the idea
of canals on the planet Mars was Schiaparelli, the Italian astronomer. Now he reports his
observations of seas and canali on the surface of Mars. Now canali actually means channels, but it was taken to mean canals. The significance of the difference between canals and channels
is that canals are artificial, they're made by humans, whereas channels one can
imagine those being formed by the various geological processes in the formation of the planet. However, the idea of channels,
canals sorry, on Mars was popularized and folklore about intelligent life on Mars abounded. Fake news is not new, it would seem. Well the American businessmen, turned astronomer, Percival Lowell who founded the Lowell
Observatory in Arizona, devoted his astronomical endeavors
to searching for evidence of intelligent life on Mars. But after his death in 1916, when there was no longer
a living proponent for the existence of the canals and therefore the existence
of intelligent life on Mars, the consensus of opinion
really turned against it. But I think we can have a
sense of how that idea grew up because we know that eyes
can play tricks on us. We know that optical illusions
can confuse the brain. Let me show you an example of that. So just a kilometer or two
away from where this lecture, here in Bernard's Inn,
is coming to you from, is St. Paul's Cathedral. If we imagine the Moon
high in the sky above that, we see it as a very big object, subtending quite a large angle
in our view of the landscape. If the Moon is a lot closer
then a great many folk report that the lower down Moon is
rather smaller than the Moon that's at the top of this photograph. In fact, these two images of the Moon are absolutely identical in angular size. But because when we look at the sky, we're not just dealing with our
eyes as inanimate detectors, we also very much involve the brain which sometimes helpfully,
sometimes unhelpfully, puts it's own interpretation
on what we see, then there is scope for humans
to get a little bit confused. Well, for a really definitive answer of what the surface
landscape is like on Mars, you can't beat a satellite, ideally one costing a billion US dollars to give you a good picture
of what's going on. So this is NASA's Viking Orbiter. And it has revealed that Mars has craters, just like on the Moon,
although fewer of them, because the Moon, sorry,
Mars does have an atmosphere albeit a rather thinner atmosphere
than the one on the Moon. The Viking Orbiter found
quite a lot of evidence of geological forms,
including volcanic activity, or at least past volcanic activity. It also confirmed the
idea that the polar caps, again, we're seeing the South Pole here, very much capture ice, water
in it's solid form of ice. So a billion dollars certainly gets you some pretty impressive images from another planet in our solar system, another rocky planet. But I'm going to show you next, an image from the ground from Australia, which is approaching the kind
of state of the art image that you can indeed hope to
get of this particular planet. So it's very rewarding to get to know Mars and to study it as it rotates and as it moves through the sky. But Mars is a rather bright planet. Relative to some of the other things that I'm going to be talking about, it's very bright indeed in the night sky. It's one of the brightest
things that we can look at after Jupiter and so on, of course. But how do we look at fainter
things in the night sky? Specifically, how do we go
about seeing in the dark? Well, when you first go
outside, on a dark clear night, free of clouds, free of raindrops, even if it's beautifully dark
and the sun has long set, you probably won't see
a thing straight away. And that's because
you're not dark adapted. But if you stand for a few minutes, then sooner or later, it becomes possible to discern different
objects in the night sky. It can take a while. It's usually better to
look at the night sky when the Moon isn't there, unless you want to study the Moon itself, because we get a huge amount
of light from the Moon. The Moon reflects something
like 7% of the light that is incident upon it from the sun. The Moon itself is a big lump of coal a spherical lump of coal, by the time you're squirting
a lot of sunlight at it, and we know the sun is dangerously bright, when you reflect 7% of that light, it's still very bright indeed. So you may just be able to make out that the top of the image, Venus. And then further down
to the right, Jupiter. It takes a while to be able to
see things in the night sky, even when it's clear, even when it's dark. And that's for two reasons,
the process of dark adaption which is the means by which
humans can see things at night is for two reasons. So the first crucial ingredient about getting dark adapted is time. You need to allow time, you
need to give yourself time before your eyes will re-engage gear from being adapted for
your modern household, presumably with electric lights and all that kind of good stuff, you need to allow time to
get dark adapted in two ways. The first of which is your
pupils need to dilate. When light levels are low, then pupils typically dilate,
acquire a larger diameter to let more light in and
to see fainter things because they can collect more light, because they have a larger aperture. This typically doesn't take too long. I'm talking a few minutes or so, perhaps even in an extreme case. But the bit that takes a long time, but that gives you the most advantage, is when something called
rhodopsin kicks in to our retina and plays it's role. This is something that massively increases the sensitivity of our retinas
to very low intensity light. This cannot be rushed. You really do need to
wait 30 or 40 minutes, if you want to look and
see things in the night sky in order to feel the full effect. But the rhodopsin in
our retinas is amazing, it can increase what we can see by a very significant amount indeed, if we allow time for that
process to take place. But there's a second thing that we can do to massively increase what
we can see in the night sky. And that is to use averted vision. So we don't want to
use direct vision here. We want to use averted vision. Why am I saying this? Well, the eye has two
different types of detectors, two different types of cells. So the first one of these
that I'm going to describe are the so-called Cones. So the Cone cells in our eyes are the cells that are
responsible for color vision. They can be sensitive for those of us blessed with good eyesight, in the red or the green or the blue. Collectively those signals
then get synthesized together, by our brains, into a color image. These are the cells
that are working for us delivering images to our brains, if we are looking at
something straight on. However, the second type
of cells in our eyes are known as Rods. There are vastly more Rods
throughout our retinas in the periphery of the
light receiving surface outside of the main density of the Cones. And the amazing thing about Rods is that they are sensitive to
very low, light, sensitivity, very low light levels indeed. There are a lot of them. And if you have a lot of detectors, even if you're only
getting one photon here, one photon here. If all of those detectors are feeding the signal to
the brain, then you end up being able to see a whole lot more, if you use averted vision. What do I mean by averted vision? Simply that you look off axis
by about 10, 12, 15 degrees, something like that, so you're no longer looking
directly along the line of sight to the astronomical object of interest. If you look off axis a bit, then the light from the
astronomical object of interest lands on the Rods, those cells
that are really sensitive to low intensity of light. And you really want to be able to do that because when you look with averted vision, rather than with direct vision, your eyes can then be
40 times more sensitive than direct vision. But again, you need to
allow that half an hour at the start of observing. So what sort of things can
you see in the night sky? Well, even in July, when in the UK it doesn't get astronomically dark, you could see some beautiful sites. And one such site, many
of us were lucky enough to be able to see was Comet NEOWISE, shown here in all it's colorful splendor. Now, you could do an amusing
experiment with a comet, if you looked at it in direct vision you could see it was there and it had a bit of a tail going upwards. If you then looked with averted vision, the tail became about four times longer. So it was a fun object on which to practice
using your averted vision. Of course, the image that
I'm showing you here, I took with my DSLR
camera, my digital camera. And I'm now here going to show you a different kind of Lucky Imaging, if I zoom in even further, while I was totally focusing
on the beautiful Comet NEOWISE, in this four second exposure, I was lucky enough to capture the meteor that you see heading
off towards 10 o'clock. I could not have planned
that, I could never repeat it. This is an unusual kind of Lucky Imaging. So averted vision is how you
see more in the night sky. So what might we be able
to see in the night sky in the coming months? Well, we're getting to the time of year where Orion and the Pleiades, that I discussed in quite some detail in my sixth Gresham lecture in May, the one called, "Perceptions,
Expectations and Discoveries." And at this time of year or as we go more towards the
end of the calendar year, we can see the beautiful
constellation of Orion, named after the hunter. We can see the very bright star Aldebaran and we can also see the Pleiades. These, remember, are that group of stars that always characterize
the last few months of the calendar year, and in the Southern Hemisphere, they are a signal that it's time to start growing crops for the Spring. This is a very important sign
in Latin America, for example. So I'm going to show you
now a beautiful image of the Orion constellation. This one is taken by Will Gater. This was taken just after the
new year at the start of 2020. And for those of you who do
know the constellation Orion, you'll recognize the two
stars in the top of the image comprising the shoulders of the hunter, the belt going across
the three stars there, the sword pointing down and
then the two stars at the bottom pointing to the tunic. This is quite a famous constellation and I gaze at it whenever
I get the chance. Will Gater took a number of images in the early weeks of 2020. And you may get a sense that there's something a bit different between these two images. I think these images
were taken in Dartmoor, somewhere, fairly dark. A few weeks later, he took another image. And I wonder if the transfer function of the various projection
software is up to it, whether you get a sense
that that orange, red star, towards the top left, is maybe a little bit
different in the left image, from what it is on the right image. This right image is
rather harder to discern because it was taken where there was greater light pollution, I believe in one of our cities. If I know show a zoom in
that Will Gater prepared, just of that star in the top left, whose name is Betelgeuse, by the way. And if I show you a movie based on this then I hope you'll get a sense that while the other
stars in the background remain very constant in brightness, Betelgeuse itself is going from bright to not so bright to fainter. The fact that the background light is brighter on the third image is a consequence of light pollution which is a great hindrance
of optical astronomy. So at the start of the year, many people were rather fascinated, how could this famous star in Orion, the wonderful orange, red Betelgeuse, how could it be going so dim,
how could it be fainting, what on Earth was going on? Excitement began to build. Some people wondered whether Betelgeuse was about to undergo
a supernova explosion. And that would have been pretty
exciting, had it happened. It is likely that one day Betelgeuse will go into supernova, but possibly not for another 10,000 years, we'll have to wait and
see, or at least wait. So why did the fainting
of Betelgeuse happen? Why did it go so faint? The most likely explanation seems to be that this star spat off a lot of hot gas. Now stars can do this from time to time, and our own sun is no exception. From time to time bits
of the plasma in a star are just spat out as that matter boils off and is injected and
launched into outer space. What happens to that hot gas once it's launched from the star? Well, that hot gas will cool
as it goes into outer space and as it expands. And when matter cools it
can condense and coagulate into what we call dust. Dust is the word that astronomers use when they mean soot, i.e. black stuff, that absorbs light and attenuates light. So if that process has happened, a whole lot of hot gas,
hot plasma has been ejected and then it's cooled and
it's condensed into soot, along the line of sight to Earth, you will absorb the light, you will have attenuated the light. And that will cause
the star to appear dim. And so that's the current best explanation for why Betelgeuse went so
faint in the first part of 2020. It does oscillate around quite a lot. And so it's true to say that this object is still
being studied, in great detail, by telescopes around the world. We don't know for sure
what it's going to do next. Now we mentioned that the
third of these images, this one here, goes quite bright, it's got a bright background. And that's because of terrestrial lights. I don't know where the
third image was taken but I feel sure there would
be lights from nearby shops or residential houses or streetlamps, something of that sort, making it much harder to see
the faintest and finest stars that are possible in the darker images. So I want now to dwell on
the fact of the question of, how can we see the night sky? It really matters that you
look somewhere where it's dark, somewhere where you haven't got
pollution from street lamps, from houses and from
shops and school buildings and so on and so forth. If you're looking for something
of a hibernation project, you might like to get
familiar with everything that has been curated on this website by The Commission for Dark Skies. They present a compelling case of why it's important to keep the the skies dark for astronomy. That matters greatly to me
as a professional astronomer and also for everyone else who cares about being able to see the sky clearly. The night sky is an area of
special scientific interest, an area of outstanding natural beauty, and indeed it is if
you can actually see it and it's not overwhelmed
by terrestrial light. But light is not only important, or the absence of light is not only important for astronomers. Light pollution confuses
cute furry mammals, insects and bird life. And so, besides the astronomical reasons for which minimizing light
pollution is important, we know, many studies have shown, that both humans and animals
sleep much more deeply, which is important for good health, when it's properly dark. There's and organization in Canada who have collected together a different symptom of the
perils of light pollution, from cities at night. The organization called FLAP,
this is their logo here, which I always find very disconcerting because birds should not be that way up. But what FLAP has done
is to collect together all the dead birds that have been killed by flying into illuminated
buildings in Toronto at night. And they've laid them all out here. These are the cadavers
of all the dead birds that flew into illuminated
buildings at night. Artificial light from buildings and city scapes endangers birds. Many species of birds migrate at night, using light from the Moon and the stars and even the setting sun to navigate. But the bright lights of our
urban areas confuse these birds and pull them off course out of their way. And so actually it's thought
to be millions of birds that are killed annually on migration, when they become
disoriented and exhausted, circling and flying into
brightly lit structures. There are lots of reasons
why it's a good idea to minimize light pollution. So I do commend The Commission
for Dark Skies to you. But back to Orion, back to what we can see in our night skies in the coming months. So this is the sort of image
that can be seen or taken with a digital camera. At least if you've got it
on a very stationary support such as a tripod. If you live somewhere really dark, in the Outback in Australia, then you can see in this
same direction in the sky, a much deeper picture. This is actually taken
with a small telescope and you can see if I go
backwards and forwards, the same stars of the Orion
constellation are there, but because the constellation of Orion is spreadeagled across
the plane of our galaxy. When you are somewhere dark, you see vastly more than
you would have expected from a relatively light polluted sky. I wonder if you can see in
the region of Orion's sword, a rather bright Nebula, which I'm indicating with
this blue arrow here. This particular Nebula
is a very famous one, it's sometimes called the Orion Nebula because of it's location. It's sometimes called Messier 42, the 42nd object in Charles
Messier's collection. It's been studied for many years and admired and cherished for many years. One of the very early people
to study it, in great detail, was John Herschel, son
of William Herschel. And this is a drawing that he made of this particular region in
the sky, the Orion Nebula, referring to an eyepiece, which was far from the
pristine optical quality that's available to us today. And patiently, patiently sketched the stars that he
could see, those are the dots, and the extended plumage
or I should say Nebula, the gas that's radiating because of the light coming
from those hot stars. This is actually an inverted image. He would have sketched
with a pencil or something on white paper, but I
think it's a bit clearer to see in this very
helpfully inverted image, which was described in an article in Sky & Telescope, a few years back. It may seem to you that dwelling on and admiring
a drawing of the night sky is perhaps a little archaic
and belonging to yesteryear. Not a bit of it. Let me show you a modern day drawing of this exact same
region in the night sky. This beautiful image,
which surely is a of love was drawn by Howard Banich
in the United States. And the exquisite attention to detail here is something I am in awe of. You can see in great detail, some of the details and structures
in this beautiful Nebula that is illuminated by the stars within. I think it's a safe bet to assume that Howard Banich has rather better optical quality eyepieces than were available to John Herschel. But there's no getting away from the fact that the hours and the dedication and the attentive eyes he must've used to create this beautiful
image, are truly breathtaking. I'm now going to show you the same image but in a multicolor format. And I hope that that again,
reproduces reasonably clearly by the time it gets from
my computer to yours. I want to draw your attention
to something that tells me of the attention to detail
that Howard Banich showed in producing this image. I'm going to focus on the
stars at the very center. These are often known
as the Trapezium Stars, on account of the four bright ones form the shape of a trapezium. I hope you might be able to see that just outside these four bright stars and a few fainter ones that are nearby, it's as though, on this drawing, they're sitting in a slightly dark halo. That is the signature of an
accurate drawing by a human. Why do I draw attention to that? Well, there's an interesting detail here. Those stars stand out
against a dark background, but if I know show you an
image of this same Nebula taken with a telescope. And this one I'm showing you here is taken at the Global Jet Watch, school observatory in India that I described to you
in my third lecture, the one that was entitled,
"The End of Matter" just over a year ago. You can see the very bright region where those trapezium stars are. If I zoom in even closer using a slightly different camera system then you can see there is no
evidence of that dark halo around the stars, that
were faithfully reproduced in Howard Banich's drawing
and also in the drawing, centuries earlier, by John Herschel. What's that all about? Did they make a mistake? On the contrary. They both drew, Howard
Banich and John Herschel, they both drew exactly what they saw. The important detail here is that when you look
at very bright things, when human eyes connected to human brains look at very bright things, our eyes and our brains are overwhelmed by the bright signal from
the stars being looked at. And so no light is detected from their immediate surroundings. Those drawings faithfully show what the human observer sees. But in reality, there is
no dark pool around them, there is no dark halo around them, just radiating light reflecting, in some sense, re-radiating the light from those
young, new, hot stars. The Orion Nebula is a region
of ongoing star formation in our universe. And while I have never had
the time or the patience and indeed probably I
lack the drawing ability to do anything approaching what John Herschel or
Howard Banich have done, I'm in awe of it and I greatly
admire that important detail that authenticates the
way their human eyes work and being faithful to the
data as they observe it, at the same time as being able
to understand and reconstruct the astrophysical reality. It is fascinating how eyes work. It is fascinating how for
all their imperfections, their non-linear responses and their vulnerability to miss
interpretation by the brain, it is nonetheless
fascinating the contribution that eyes can make to
astronomical endeavors. I'm showing you here an image which I showed in my lecture in May, the one on "Perceptions,
Expectations and Discoveries" of Messier 1, number one in
the catalog of Charles Messier. You definitely need a telescope for this particular object, by the way. This particular object came
into existence a millennium ago, it was observed by the Chinese in 1054 as a supernova explosion that then ejected into
outer space, all this debris that we now observe as the Crab Nebula. This particular object
is a favorite to look at, if you've got a reasonably
good size telescope. This particular object,
the Crab Nebula, Messier 1, was being observed at
the McDonald Observatory, one night in 1957, when
there was a public open night for the telescope that they had there, which is 82 inches in diameter, it's about two meters in diameter
longer than I can stretch. This particular telescope was
focused on the Crab Nebula that I had in my previous slide. And I'm showing her a picture
of Jocelyn Bell Burnell because she told me a
very interesting story about something that
happened on that open night, that observing night, in 1957. She relayed to me a story
told by Elliott Moore of how the public stepped up in turn to take their turn at
looking through the eyepiece on this huge telescope,
at this particular object, the Crab Nebula, in particular,
Minkowski's star within it. So one member of the public
stepped up to the telescope and said to the night assistant,
"That star is flashing." So the night assistant started to explain to that member of the
public about scintillation. Scintillation is something we're probably all fairly familiar with. Another name for it is twinkling. When we look out and see
twinkling in the night sky or scintillation in the night sky, that's the phenomenon that was giving rise to the blurriness and the
bouncing around and the bobbing in my movie sequence of Mars
at the start of this lecture. Twinkling is kind of all very gorgeous when you're looking at the night sky, but it's not so great
if you want to focus in, in great detail on one particular object. So as the night assistant,
the telescope operator, at this public open night
at the McDonald Observatory was about to launch forth into an explanation of
scintillation and twinkling to this member of the public, who was saying, "I can
see that star flushing." She politely pointed out to him that she knew all about scintillation because she was a pilot and
was used to flying by night. This is rather amazing
by the way that in 1957, a young woman should
hold a pilot's license. So this member of the
public flies at night, knows the night sky, because what else is there
to do in a dark cockpit, in a plane by night? And so she knows about scintillation. And she's very insistent
that what she sees, through the eyepiece, attached
to this huge collecting area of an 82 inch telescope, she is insistent that
that star is flashing. Why have I drawn your
attention to the fact that it was Jocelyn Bell
Burnell who told me this story? That flashing star turned
out to be the Crab Pulsar. So human eyes can see ahead of their time. If they're very clear and very
honest about what they see, then that can lead us
to remarkable insights into what's going on in the night sky. So it's in the center of this Crab Nebula, in the center of Messier 1, that resides the Crab Pulsar, which Jocelyn later discovered, some years after this young
woman at that public open night, at the McDonald Observatory,
reported it to be flashing. Well, it is certainly
true to say that our eyes, if appropriately trained and well adjusted to seeing at night,
can see amazing things. Back now to John Herschel and a different, very beautiful Nebula in the night sky. This is possibly one of my favorites, not so much in this early version, because again, in the
times when John Herschel was observing, the optical
quality of his eyepieces and indeed telescopes were
really not that great, relative to modern standards. This is really an object
to see in all it's beauty with a telescope. And I think this really is
one of my favorite Nebulae in the whole sky, Messier 8. Again, gas surrounding a region of current ongoing star formation being illuminated in all
it's glorious swirls. This is one just with a very
slightly different color scheme taken from my Global Jet Watch
school observatory in Chile. So telescopes and eyes together can help us form a really good picture of what's going on in the night sky. What are the analogies, I wonder, between how telescopes see
or cameras on telescopes see and how I see? What are those analogies and
how does this all fit together? Well, this movie was prepared
with the help of Lucy Wright. And I hope it shows very clearly, or will show when I start playing, how the eye and the brain function compared with how a telescope
and a camera function. So let's watch this movie now and you can see that
light obviously passes from the apple, or whatever,
through the cornea, through the aperture formed by the iris, being focused a little bit by the lens onto the back detector of the eye that I mentioned earlier, the retina, and then that light
signal goes to the brain and gets interpreted there. Whereas, for a telescope and a camera, let's say that we're looking at the Moon, we've got rays of light passing onto the primary mirror,
onto the secondary mirror, being focused onto the
detector, in this case, a camera controlled by, stored by a computer. How much the eye and the
aperture actually see depends on the size of the aperture. The more your pupil is opened, the more light you will collect. That's why you need to
dark it out at night. For a telescope, you
can't change the aperture, you can't change the aperture, you can't change the collecting area. You couldn't buy or borrow or look at someone else's larger telescope but really your collecting
area is fairly fixed. But there's one key advantage that using a telescope
and a camera system has compared with using the eye. And that's the following. With a camera you can
expose for a long time. So when light impinges on the eye and lands on the back of the retina, typically it's the light averaged
over 1/10th of one second or 2/10ths of one second that gets collected and then interpreted as an image by the eye. Whereas, with a camera you
can set the exposure time to quiet a range of different values. So the image that I
showed you a bit earlier of the comet with the
meteor nipping nearby it, that exposure time was four seconds. With a camera, I've taken exposures which have been an hour long in length and of course seen very, very faintly, very, very deeply into the night sky. There's basically no chance
of saying to your eye, "Look, come on, integrate for longer "than a 10th of a second or
two, collect more light." If you want to increase the exposure time and collect more light to see more deeply, it's time to turn to a camera. But you can assist your
eyes in different ways. One way of collecting more light so that you get more light
landing on your retina is to use an eyepiece and
a telescope of course, or the very best way, if
you're just getting started in observing the night sky with your eyes, is to use a pair of binoculars. Brains typically work best when they're using light
from more than one eye, two specifically, is quite
a good number of eyes. Binoculars collect that bit more light, they focus it and we then
get a stronger signal of fainter targets in the night sky. So there are important differences between observing the
night sky with our eyes or be it with some kind
of optical assistance like binoculars and using a telescope. But it is important to emphasize that even this bottom route, using a telescope, using a camera, those camera images, nonetheless, still get interpreted by the brain. This arrow here says to the computer, but who operates the computer? That's a human. And so interpretation of astronomical data is a really big deal and is something else that one could, in principle, bring non-linear or
prejudicial perspectives to. But the big difference
between using the eye and using the telescope,
as I've indicated, is collecting area. So I'm going to show you something of a self portrait right now. This is taking a photograph
with my digital camera looking at the primary
mirror of my telescope at the school observatory, part of the Global Jet
Watch network in Chile. So the diameter of my
retina is a few millimeters and that can see so far at night. The diameter of the aperture
of that particular camera lens is a few centimeters, so
that can collect more light and I can see more deeply into space than I can just with my eyes. But the diameter of this
particular primary mirror is half a meter. And so that's why we can see
that very beautiful Nebula of Messier 8, that I showed
you a few slides ago. Collecting area really
does matter for astronomy. Size matters, when you're talking about the size of the light bucket with which you are
collecting light signals from different parts of
the galaxy or beyond. Let me talk about something
a little different that we might hope to
see in the night sky, in the coming weeks and months. So I started this particular lecture with a conjunction of Mercury
and Jupiter and the Moon. A conjunction again, is where two planets or other known stars come very, very close
together in the night sky. They're only close together
in an angular sense. They're not close together
in a radial sense. But close together as they
appear to us on the sky is a very beautiful sight indeed, as you saw from the
first astronomical image that I showed you in this slide. I want to talk about a very
special kind of conjunction now. This is one that astronomers refer to as a Great Conjunction. So a Great Conjunction is specifically where the two planets
that come close together are Jupiter and Saturn, the most majestic of the
planets in our solar system. When they form a conjunction it's called a Great Conjunction. Now the last time that we
had a Great Conjunction, visible from Earth, was in 1623. In 1623, Gresham College was still only on it's third professor of astronomy. 1623 is quite a long time ago. The last time Jupiter and
Saturn came close together was 1623, a few centuries ago. The next time it's going to happen is in just a few weeks time. So what I would suggest is
that if you have a good view to a Southwest horizon,
you start looking out for where Jupiter is in the night sky and where satin is in the night sky. Don't worry if you haven't
yet practiced and mastered the dark adaption techniques or the averted vision techniques that I referred to earlier in my talk. Jupiter and Saturn are super bright, they are in your Southwest horizon. And if you watch them whenever
you got a clear night, in the coming few weeks, you will see them get closer
and closer and closer together. Closest approach will be
at about 6:00 p.m, UK time, about 6:00 p.m on the 21st of December. So if you're looking for
a hibernation project during lockdown Winter, I really recommend looking at
the night sky with your eyes. Let me give a health warning that warm coats and warm boots have been known to be an asset
when looking at the night sky from this particular part of the world. If you want to look at
this great conjunction on the 21st of December, start looking now while you get used to what your eyes are seeing. Seeing and understanding
what is in the night sky takes practice and takes training. And if you want to have a
context for the special event that's happening on the 21st of December, less than two months from now, the last example of which was in 1623, start looking now and watch them getting closer and closer together. This particular image
shows Jupiter over there, Saturn there and a couple of bright stars. So if you see that
rhombus gradually forming and you may well find it easier with binoculars or something, Jupiter and Saturn will be
only 1/10th of a degree apart on the 21st of December. Then if you can see it,
you're in for a treat. But prepare yourself for it by watching them come close together. What else can human eyes
do in terms of astronomy? Believe it or not, what human
eyes see in the night sky can contribute to research
in professional astronomy. Let me show you how this happens with a few slides kindly
given to me by Stella Kafka who is the director of the AAVSO, The Amateur Astronomers
Virtual Observatory. So what Stella has been
a great advocate for and a very successful advocate for is people who look at a
particular group of stars, flagged up on their
website as being important for professional astronomers,
on a particular night, and to capture and record faithfully and honestly what they see. So the way it goes is the following. Imagine that the star that's delineated by those two horizontal lines has newly appeared like a Nova explosion. What we in the world of
professional astronomy really want to know is,
how is that changing, in what ways is it changing
and how fast is it changing? Now the problem is not all
telescopes, far from it, are available to observe
changing phenomena in the night sky. That's why I instigated the
Global Jet Watch telescopes. But even then telescopes,
if they're pointing at a different phenomenon
in the night sky, can't necessarily stop what they're doing and look at a newly appeared
star in the night sky. So what Stella Kafka and the AAVSO do is they ask people, they encourage people, to watch what's happening and to make a comparison
of the newly appeared star with nearby stars that are unchanging and whose brightness is
known and calibratable. So you can answer questions like, is the newly appeared star delineated by the horizontal lines, brighter or fainter than star 91? Today, the 10th of June in this example, it's quite a bit brighter than 91. Is it bright to the 85? Yes it is. Is it bright or the number 75? Yes it is. Is it brighter than number 64? Yes, it is. Brighter than 61? No. So you have then bounded the
brightness of the new star between number 64 and number 61. You do the same game, few nights later, you do the same game, even
if it's cloudy, by the way, you can still do this
same kind of analysis because as long as you haven't
got overly granular cloud then the relative
brightnesses of the stars will remain the same
relative to one another. On another date, you might see the brightness of the
star change even further. And you can capture this and then plot it. So a plot in astronomy, against
time, on the horizontal axis and with brightness, doesn't
matter what the units are, they're relative to the nearby stars, if you plot the brightness, that is something that is
known as a Light Curve, a time series of brightness data for a particular star in the night sky. If you keep going with that, and if you're joined by
friends all around the world who are either just using their eyes together with binoculars or
maybe with a digital camera or maybe they're lucky
enough with a telescope, collectively, lots of
points can be plotted to get the desired Light Curve. Let me explain to you
why this data collection, this light gathering and light
comparison game or exercise is so valuable. I'm going to show you now a Light Curve of the brightness of a newly
exploded star called a Nova, which went off in Sagittarius in 2015. As with all Light Curves, we've
got time on the bottom axis, the units here a days since detonation, and then I've got a particular axis which represents the brightness of stars. I don't know about you but I think that's a
pretty scruffy Light Curve and it's quite hard to
understand what's going on. These are the only Light Curve data that were available for telescopes in the first weeks after this
particular Nova exploded. However, if I now overlay on this plot, the data from human
observers all over the world, collected thanks to the work of the AAVSO, you can see much more clearly the zigzags and up and down changes in the brightness of this particular Nova explosion,
which is exactly what we, as professional astronomers
studying over explosions, really, really want. As time went on, this was in sort of late Spring, early Summer of 2015, things evolved really quite dramatically. There was a sudden drop in the brightness which is basically when
a whole lot of matter was thrown off the star, just
as in Betelgeuse's dimming, that I referred to earlier in my talk, the brightness of the star plummeted, it became a whole lot fainter,
you can see the dip there just after a hundred days, and then it gradually recovers. It was absolutely brilliant. It is absolutely brilliant to have the complimentary
data from the AAVSO, all the way around the world, filling in the gaps and
filling in the dots. There's more scatter
on these measurements, more uncertainty in them because
humanized are not perfect and all that sort of thing. But that still means they are
scientifically useful to us. So hurray for the AAVSO. One of my graduate students,
Dominic MacLaughlin and I are studying this particular
Nova explosion in Sagittarius, looking at all sorts of
changes in the spectra of this particular star, as it evolved, this is very early stage. As these signatures move
around and go up and down, it is massively helpful to have
those filled in Light Curves from friends and supporters
around the world. So again, if you're looking
for a hibernation project, I recommend that during
this lockdown Winter, you take a look at the
website of the AAVSO. I hope this has given
you a sense of everything that human eyes can see. And that despite the
imperfections of human sight, despite the fact that human eyes are non-linear in their
response to the light that lands on our retinas, despite all of that, observations, attention to detail of what's going on in the night sky can still be fantastically,
scientifically useful if we have faithfully attentive eyes. And that's the end of
my lecture, thank you. - Thank you very much Professor Blundell, for a really fascinating lecture. I do have a couple of questions
from our online audience. A couple of them deal with equipment. One of our audience members is interested in the size of telescope
used for the video of Mars. - So the, the telescope that was used for the particular video of Mars was a relatively large one, by amateur standards, it was
about 14 inches in diameter. But I'd like to hasten to add, you can get similar images that give you the same
qualitative features of the the different
colored surface across Mars and of it's rotation, even with a good digital
camera and a good lens, if you've got to tripod. I sometimes think that the
most important equipment for doing these kinds of observations isn't necessarily the fancy optics but it's the stability of your tripod and the warmth of your
coat and your boots. I hope that helps. - How machines able to
take pictures on Mars while dealing with external factors for example, dust, radiation, et cetera? - That's a very good question. And the answer is, it's not easy. So any images that are taken, whether they're with human eyes or with cameras and telescopes, on the ground or in satellites, for any of those data that are
being captured and recorded it's crucially important that a process of calibration takes place. In that little game of the
AAVSO, that I was illustrating, where in turn you say, "Is
this new, exciting star "brighter than this star,
fainter than this star today, "compared with yesterday?" That process is actually
called photometric calibration. Calibration is the means by
which we can take imperfect, flawed, non-linear observations
of what we see in the sky and turn them into
scientifically useful data. But it's absolutely fair to say that even for cameras on a satellite, cameras on a telescope, calibration is absolutely a
crucially important process. In the case of dust, dust
can reradiate infrared light. And that's something
that we absolutely seek to subtract out very, very carefully from the images that we study. So to are things like cosmic rays, which will be the subject of a lecture that I'll be giving in the new year. Calibration is crucial,
whatever you're doing. But your understanding of how you need to do that calibration whether you're looking by eye or looking with a telescope on the ground or with a satellite, that absolutely is something
that's informed by experience and by the curiosity and the inquisitiveness of human nature. - Thank you. Does the lack of cratering on
Mars, compared to the Moon, suggest that the cratering
primarily occurred back when Mars had an atmosphere, before it lost it's magnetic field, surely today's atmosphere would
not burn up the meteorites? - That's a very good question. There are certainly some
craters on Mars, as I mentioned, fewer than are on the Moon
more than are on the Earth. And I think exactly why there
are few relative to the Moon which has I described in
a previous Gresham lecture are so numerous because the Moon basically doesn't have an atmosphere, so nothing burns up on
route to going splat on the Moon's surface. That very much depends on
the history of the evolution, of Mars itself, the geological formation as well as on the evolution
of the atmosphere. So it's an interesting question and I don't think it's
entirely, fully resolved as yet. - And one final question on equipment. Could you suggest optimal
size/strength of binoculars for sky watching? I much preferred using two eyes to one. - I absolutely agree with the sentiment that using two eyes is much
preferable for astronomy because our brains have
evolved to work with two eyes and get stereo vision. So absolutely do get some binoculars. Quite what you go for, I
think, depends on your eyes and where you are going to be observing. If you're observing from the UK, then maybe what you want
is a little bit different from if you're going to be observing from the bush in South Africa
or Botswana or somewhere. So what I would do is read around on the websites of Sky & Telescope or Sky at Night or Astronomy Now, and look into the various pros
and cons and relative merits. It doesn't need to cost you a fortune to get a really super pair of binoculars that will massively enhance your night sky observing experience. Don't rush into it though,
I'd read around it first and make sure you're making
a really good choice for you in the context and
location that you're in. - That's wonderful. Thank you again for a great lecture and for your willingness to
answer questions as well. Thank you all for
attending this afternoon. I'd like to encourage you to return for professor Blundell's next lecture, which will be held on Wednesday the 18th of November at 1:00 p.m. And that one is, "Cosmic
Vision, Witnessing Fireworks." See you then.
