Her e at the university of Arizona we make the largest mirrors in the world. So astronomy is limited by light gathering
power. When you want to look far in the universe or look for faint stars or exoplanets, you have to gather as much
light as possible. So the push is on to build bigger and bigger telescopes and we’re building the mirrors for those big
telescopes right here. Here. [MUSIC] The mirror behind me is one of what will be 7 mirrors, all of this size, that will
go together like flower petals with a central piece to make the biggest telescope in the world. Basically, a 24 meter
optical telescope called the giant Magellan telescope that’s destined for Chile. And we, University of Arizona and
Stewart Observatory, we’re 10% partners. This is a billion dollar project, this is big science in every sense of the word.
My name is Chris Impey, I’m a University distinguished professor of astronomy at the University of Arizona and I’ve
been here for almost 30 years doing research on super massive black holes and distant galaxies and teaching
astronomy. This online course, Astronomy, Exploring Space and Time, is the culmination for me of teaching to a very
wide audience to try and convey the excitement of astronomy and especially the research that’s going on right now,
which is all around us at Steward Observatory.
Play video starting at 1 minute 24 seconds and follow transcript
1:24
So this course is an overview of astronomy. Nothing is left out. We’re talking about everything from comets to
cosmology and we’re talking about how we know what we know. That’s important. How can we prove or understand
the universe 13.7 billion years ago in the big bang, how do we know what it’s like inside a star? How do we know
there are planets that might have water on them light years away? So the method of science shows us that we can
use evidence, remote information, remote sensing, light and other electromagnetic radiation to learn these things.
And then we talk about the tools and these are the amazing new tools of astronomy, these huge telescopes and also
huge detectors. And so the progress of the class goes inside out, you know. It starts from our neighborhood and
works out through the solar system to twins of our solar system, and perhaps, earth clones that we might be finding
into the architecture of the Milky Way and all the exotic end states of stars, which are interesting to a lot of people.
Black holes and neutron stars, places where relativity is dominant and where space and time are warped and
distorted and then out into the universe of galaxies, and then talk about the whole thing. Cosmology, the study of
the universe, as a single entity. [MUSIC] These tools are very sophisticated and very expensive. This giant Magellan
telescope will, in the end, cost about a billion dollars, so this is big science. But astronomy really starts with curiosity.
It starts with something that costs nothing. It’s built into every human brain, the curiosity of where we come from,
what is our position in the universe, and what’s the nature of the universe? So I hope everyone enjoys this class and
interacts with me and the material and gets a flavor of modern astronomy.
About the course
Why experience the universe?
Astronomy is one of the most dynamic fields in all of science. There are new discoveries almost daily in the
areas of exoplanets, black holes, distant galaxies, and cosmology. This excitement is driven by technology that’s
enabling a new generation of large telescopes on the ground and in space. The quest to understand our place in
the universe is as old as humanity itself. So join us and experience the thrill of astronomy!
Why take this course?
This course surveys the state of the art of astronomy, from the Solar System to the edge of the observable
universe. In just six weeks you’ll learn how astronomers are learning about remote regions of time and space.
You’ll also see how the scientific method works to expand our understanding, and how a small set of physical
ideas underpin all the complex phenomena of the universe.
What you will learn.
You’ll learn the rich history of the oldest science, where the night sky has been embedded in culture for
thousands of years. You’ll learn about the techniques for building large telescopes, and ways we have expanded
our vision far beyond the familiar realm of light. You’ll learn about robotic probes that have studied the Solar
System and identified places where life might be found. You’ll learn about the birth and death of stars, in
particular the exotic end states that give us new ways to test the theory of gravity. You’ll learn about distant
galaxies and attempts to understand the enigmatic dark matter and dark energy that control the cosmos. You’ll
learn about the quest to find life beyond Earth and the huge number of habitable worlds that have been
projected in the Milky Way galaxy.
How you will be able to use what you learn.
The content of this class can be used to understand the news you read about astronomical discoveries almost
daily. It will also help you see the connections between disciplines, since the material extends to physics,
geology, and biology. You will see how scientists use technology and evidence-based reasoning to ask and
sometimes answer profound questions about the universe. The course will give you a deeper appreciation of our
place in the universe.
There are no prerequisites.
There are no prerequisites for this class, and no prior knowledge of astronomy is assumed. The material is non-
mathematical but conceptually high level. We hope that you go beyond the video lectures and quizzes and
engage the instructor and the material more deeply by participating in live sessions, online discussions, and
social media associated with the class.
About us
Your Astronomy: Exploring Time and Space Teaching Team!
Professor Chris Impey
Chris Impey is a University Distinguished Professor and Deputy Head of the Department of Astronomy at the
University of Arizona. He has over 170 refereed publications on observational cosmology, galaxies, and
quasars, and his research has been supported by $20 million in grants from NASA and the NSF. He has won
eleven teaching awards, and he is currently teaching two online classes, one with Coursera and the other with
Udemy, with over 35,000 enrolled. Impey is a past Vice President of the American Astronomical Society and he
has been an NSF Distinguished Teaching Scholar, the Carnegie Council’s Arizona Professor of the Year, and a
Howard Hughes Medical Institute Professor. He’s written over 40 popular articles on cosmology and
astrobiology, two introductory textbooks, a novel called Shadow World (2013, Dark Skies Press), and seven
popular science books: The Living Cosmos (2007, Random House), How It Ends (2010, Norton), Talking About
Life (2010, Cambridge), How It Began (2012, Norton), Dreams of Other Worlds (2013, Princeton), Humble
Before the Void (2014, Templeton), and Beyond (2015, Norton).
Dr. Matthew Wenger
Matthew is an Educational Program Manager with Steward Observatory at the University of Arizona. He has a
PhD in astronomy education and over 15 years of experience working in informal science education and free-
choice learning. He develops curricula and assessments for online astronomy, and conducts research on
learning in online environments. He is currently teaching two online courses with Professor Chris Impey with
over 35,000 students enrolled. Prior to his current position, Matthew completed a postdoctoral position in free-
choice STEM (science, technology, engineering, and math) learning at Oregon State University, and worked at
the Adler Planetarium in Chicago, IL, as well as the Flandrau Science Center at the University of Arizona.
David Pickel
David Pickel is a Ph.D student at Stanford University studying Classics and Archaeology. His interests include:
environmental archaeology, The Mediterranean West, Roman provincial studies, and, of course, ancient
astronomy. His M.A. thesis considered human-climate interactions of the Roman Maghreb as seen in the
archaeological record. Originally from Naples, Florida, David completed his undergraduate education at Florida
State University, and afterwards continued his Greek and Latin studies at the University of Pennsylvania. He is
really good at not being so good at soccer…
Social media
Stay in touch with Prof. Impey and Astronomy: Exploring Time and Space!
• Like us on Facebook: Astronomy: Exploring Time and Space
• Check out our YouTube Channels: Teach Astronomy; Astronomy: State of the Art
• Follow us on Twitter: @AstronomySOTA
• Add us to your circle on Google+: Astronomy: Exploring Time and Space
Welcome to Astronomy: Exploring Time and Space!
This class is a survey of modern astronomy. We begin with a brief history of how science works to help us
comprehend the universe, modern telescopes, and the underlying physical principles of light and gravity. We
then proceed through modern astronomical topics and get up to date on the most recent astronomical
discoveries. There is a particular emphasis on the discoveries that are transforming our understanding of
planets, stars, galaxies and the universe. You will see what we have learned from new ground-based telescopes
and space observatories. Astronomers project the scientific method into remote regions of time and space,
discovering Earth-like worlds, probing the exotic end states of stars, counting and weighing galaxies, and
diagnosing physical conditions in the first instants of the expanding universe.
• The official “text” for this class is a free online textbook available at teachastronomy.com
• The basis of this course is a series of lecture videos between 5 and 20 minutes in length. These videos
cover the major course concepts and include helpful images and animations.
• There will be five peer-graded writing assignments about a topic related to each corresponding week, as
well as weekly lectures quizzes over the content of the lecture videos as a part of each section.
• In addition, there will be two course activities: the first will be a galaxy classification activity using the citizen
science project: “Galaxy Zoo”; and the second is an observing project using remote robotic telescopes.
• We will facilitate live question and answer sessions periodically through Google Hangouts on Air.
Announcements (including links to the session) will be sent to each student via Coursera Student email.
• Supplemental materials include: lecture slides (.pdf), optional readings, and podcast interviews with
scientists at the University of Arizona.
• The final grade is based on 18 lesson quizzes (54%), 2 activities (24%), and 5 peer graded writing
assignments (20%), and 1 short survey confirmation quiz (2%). To pass the course you must complete and
pass all of the assignments at the minimum grade level listed for each.
Lesson Themes:
1. Science and History. Science combines logic and evidence to increase our understanding of the natural
world, including remote and inaccessible regions of space and time.
• Assessments: Lesson Quiz 1a, Lesson Quiz 1b; Writing Assignment no. 1, “Science: Past and Present”
• Science Learning Survey (Link HERE) (further information found in the introductory module).
2. The Night Sky. Astronomy is the oldest science, and its history shows a growing realization of our
insignificant status in a vast and ancient universe.
• Assessments: Lesson Quiz 2a
• Peer Evaluations (x4) of Writing Assignment no. 1
• Begin collecting data for Activity no. 2, “Observing Project”
3. The Tools of Astronomy. A continuing revolution in telescope design and construction is giving astronomers
an unprecedented set of tools for exploring the universe.
• Assessments: Lesson Quiz 3a, 3b; Writing Assignment no. 2, “Telescopes”
4. Matter and Radiation. Astronomers harvest information across the electromagnetic spectrum, using spectra
to measure the composition of distant objects and diagnose extreme physical conditions.
• Assessments: Lesson Quiz 4a, 4b
• Peer Evaluations (x4) of Writing Assignment no. 2
5. The Solar System & Space Travel. Space probes have visited most planets in the Solar System, and
orbiters and rovers are homing in on the habitability of Mars. Thousands of extrasolar planets have been
discovered, including some that are Earth-like and habitable.
• Assessments: Lesson Quiz 5a, 5b, 5c
6. Exoplanets. Space exploration is entering an entrepreneurial phase that might let us venture beyond the
Solar System and thousands of extrasolar planets have been discovered, including some that are Earth-like and
habitable.
• Assessments: Lesson Quiz 6a, 6b; Writing Assignment no. 3, “Exoplanets”
7. Star Birth and Death. Stars are the crucibles of heavy element creation, and the chaotic regions of their birth
are being understood though long wavelength observations. Gravity is the ultimate victor in the life story of any
star, leaving behind the exotic end states of white dwarfs, neutron stars, and black holes.
• Assessments: Lesson Quiz 7a, 7b; Writing Assignment no. 4, “The Sun and Stars”
• Peer Evaluations (x4) of Writing Assignment no. 3
8. Galaxies. The architecture of the Milky Way galaxy is that of a disk, a bulge, and a halo, with the entire
assemblage bound by enigmatic dark matter. Every galaxy contains a supermassive black hole, and entire
population of galaxies is sculpted by gravity into subtle structures on large scales.
• Assessments: Lesson Quiz 8a, 8b; Activity no. 1, “Galaxy Zoo”
• Peer Evaluations (x4) of Writing Assignment no. 4
9. Cosmology. The expanding universe points back to an extraordinary state of extremely high density and
temperature called the big bang.
• Assessments: Lesson Quiz 9a, 9b; Writing Assignment no. 5, “Cosmology”
10. Life in the Universe. The Earth gives us a ringside seat on the physical, chemical, geological, and biological
evolution of a dynamic terrestrial planet. The abundance of terrestrial planets in remote solar systems motivates
the search for life and technology elsewhere in the universe.
• Assessments: Lesson Quiz 10a, 10b; Activity no. 2, “Observing Project”
• Peer Evaluations (x4) of Writing Assignment no. 5
In this first section of the course, we’re going to see how science works to learn about the universe. The
scientific method not only applies to understanding black holes, and galaxies, and the Big Bang, and exoplanets,
but also to understanding everything in nature, including evolution and all our other scientific theories. So the
tools we’re going to talk about are quite general across the field of science. Science starts with evidence,
evidence of the natural world, and physical or regular laws that can explain the behavior in the natural world.
Now, astronomy is not like most sciences because the evidence we have is often remote, and comes to us in the
form of electromagnetic radiation. Astronomy is not a lab science, so we cannot control the experiment of the
universe. But the information we gather is extremely powerful and diverse, and has allowed us to learn situations
that are extraordinary such as the event horizon of a black hole, or the atmosphere of a distant Earth-like planet
100 light years from the Earth, or the earliest phases of the expanding universe when temperatures were
extremely high. The evidence of science is combined with logic and the idea of building theories that explain
diverse sets of data. Science is a contingent enterprise, so scientific theories are always on their metal to be
proven against new data sets, and are always at risk of being disproven if data does not fit the theory. This has
happened in astronomy a number of times. We’ll talk about the history of astronomy which includes some of
these progressions where theories have been discarded and replaced by better theories. Mathematics underlies
astronomy and all the physical sciences, because it’s emerged over the last century that the universe is
governed by physical laws that have beautiful mathematical underpinnings. The reason for this is not completely
understood, but the explanatory power of these mathematical theories is quite extraordinary. The theory of
gravity is perhaps the most famous example of this. We will look at the nature of the evidence in astronomy and
of the theories that have come to be the most profound to explain our place in the universe. Then we will look at
the history of astronomy. Astronomy is perhaps the most dynamic science with discoveries every week, but it’s
also the oldest science. Astronomy starts with observations of the night sky, millennia before the telescope was
invented. Humans were looking at the motions of the stars, the planets, the Sun, and the Moon, and trying to
understand what was going on. Where were these objects? What were they made up? We’ll look at ancient
astronomy, cultures around the world, observing the same phenomena, and trying to make sense of them
without telescopes and really without any mathematical underpinnings, but just looking at the regularity of the
patterns in the sky. Regularity that you can see if you go out for a year and look at the phenomena of the night
sky. These ancient civilizations were not approaching the problem in a purely scientific way. That innovation
came from the ancient Greeks about 2500 years ago. With Pythagoras, and the ideas of mathematics, and with
Aristotle, and the ideas of logic, we have the basic toolkit for doing science. Science still depends on that same
basic toolkit. As we look at the history of astronomy, we’ll see that these powerful ideas gradually gave us a
more and more broad view of the universe, explaining not just the phenomena of the night sky, but the
phenomena revealed by the telescope after it was invented in the early 17th century. Then we’ll look at the
Copernican Revolution, perhaps the most profound change in the history of ideas in the history of humanity,
where from a position where we thought ourselves the center of the universe and the pinnacle of creation, we
realized that the Earth was in motion around the Sun, and was just a planet among-st other rocky bodies in the
solar system and beyond, and that the Sun was just one among-st many stars in the Milky Way galaxy, and
eventually, among galaxies beyond. This profound shift in our views called the Copernican Revolution continues,
because in the modern era, it emerges that the totality of space-time we see, the observable universe, may not
be the only universe. Perhaps, the last step in the Copernican Revolution would be the demonstration that the
biology of this planet life on Earth, is not unique to this planet, and that life exists elsewhere in the universe. We
can anticipate that astronomers will make this discovery perhaps in the next decade. This first section, we’ll try to
summarize the principles that govern science not just astronomy, but all fields of science, as they explore the
natural world.
Astronomy starts with vision. That’s not just because optical Astronomy is still the primary way we learn about
the universe, but because we have to see the universe. Astronomy is based on observation as is most science.
It’s how we see the universe with our eyes or with telescopes. And astronomy, like most scientists starts with
observations of patterns and the natural world. That’s something that’s built into everyone. Humans are built to
recognize patterns, whether it was a way of avoiding predation when we were hunter gatherers or a way of
identifying food sources with the changing seasons. We’re built to recognize patterns. We’re really good at it. It
has a survival mechanism, and it helps us a scientist to. It‘s important in astronomy and in science in general to
see the world as it actually is. In this pair of images, we’ll see a medieval view of how a cannon ball travels, and
this is based on Aristotle’s mistaken idea. From Greek philosophy of the 5th century BC where an object does
not have rest as a natural state of motion. And we can see the completely unnatural trajectory of the cannonball
based on physics that was essentially wrong. Moving forward to Leonardo’s painting of a cannonball trajectory,
we see the parabolic arc that later is described beautifully by Newton’s law of gravity. In this example, the artist,
Leonardo, correctly portrays the trajectory of the cannon ball based on observation, even though he had no
theory of gravity to guide him. The example of Leonardo reminds us that centuries ago there was not the artificial
distinction between science and the arts that there is now, which is unfortunate in my opinion. Leonardo was a
polymath who worked equally in the worlds of science, engineering, and math. Another example perhaps less
familiar as an artist was Galileo. He published his beautiful water color and charcoal drawings of the moon and
the things he saw through the telescope. Because again, remember this was before photography, before
electronic detectors. All you could record is what you saw with your eye. And recording it exquisitely with a
painting is one way of doing that. So, in Galileo’s drawings of the moon, we see the topographical features that
told Galileo this was another rocky world like the Earth. A very important part of the history of ideas, leading to
the fact that the Earth is not unique. When we talk about vision we can extend this to include other senses too.
One modern technique and science involves sonification or turning visual or numerical data into sounds. It’s one
way of understanding the patterns in nature. This was done by Kepler, who is the first to understand planetary
orbits. He talked about the harmony of the spheres, by which he meant he planetary orbit could be converted
into a varying tone based on the frequency of the orbital period and its perspective as viewed from the off-
centered position of the earth. In this audio version of that, we hear the harmony of the spheres as successive
planets are introduced with lower and lower tones moving out from the sun.
Kepler didn‘t originate the idea of the harmony of the spheres, it was an ancient Greek idea that came from
Pythagoras. Pythagoras had a profound influence on all the scientists and philosophers who came afterwards.
Saying for example that the universe was based on number. And in modern science we believe this. We believe
the mathematical, numerical theories underlying nature. Pythagoras also talked about the harmony of the
spheres. He thought that this celestial music was such that only enlightened people could actually hear it. In this
second example, we dramatically hear what the entire universe might have sounded like in the first 10,000 years
after the big bang. [SOUND] This is the sonification of the interactions of matter and radiation in the infinite
universe when the temperature was thousands, perhaps a millions of degrees. We hear the ringing of the
universe as these oscillating waves and particles interact with each other. Remember, this is the pre-cursor state
to a vast and ancient universe that eventually would contain a 100 billion galaxies. This work was done by Mark
Whittle at the University of Virginia. That’s dramatic example when we compress 10,000 years into a bad sense
seconds and because the audible range of the true physics is 42 octaves below what we could hear, we up
shifted to come into the audible range. Vision is how we learn about at the universe. In astronomy, initially, it was
with the eyes, and then with telescopes and electronic detectors. Vision also extends to other senses, and to
other parts of the electromagnetic spectrum. Vision and this kind of data is how we learn about the universe.
One of the exciting things about science is discovery. The fact that many important things about astronomy were
never predicted by a theory or anticipated by astronomers before they made the observations, we never
predicted the existence of dark energy or dark matter or black holes. But we’ve observed these things, and
we’ve observed extraordinary things in the universe that were based on surprises to people looking at the world
in new ways. As a metaphor and an analogy for discovering nature, let’s look at sequences of cards. Regular
playing cards with the face cards taken out, so just the number cards. It’s a toy model, but it meaningfully
captures some of the essence of how science works. You’re gonna see four different sequences of cards, and
the goal in this little game is to decide what is the rule that governs how these cards were laid down. what is the
pattern in nature? In this case, the pattern in a numbered series of cards of four different suits that describes
what’s going on. The first example is obvious. I don’t need any explanation for me, it’s just a numbered sequence
of the same suit. The rule is obvious. The second patter, is a little more interesting, it’s an alternating red and
black sequence. But notice here that some information is important, the alternating red and black sequence, and
some information is irrelevant. The actual numbers of the cards or the difference between the two red and the
two black suits. This is a lesson that in nature and in science, it’s not obvious what the most important
information is when we seek a pattern and don’t need understand it. But now look at the third and fourth
patterns, and see if you can decide before I give away the answer what is the rule that governs how these cards
were laid down.
You can see it’s a little subtle. There do appear to be sequences or patterns embedded in that layering of cards.
But it’s not obvious. By trying to imagine the rule, you are doing what a scientist does. You’re developing a
hypothesis and testing it against nature, in this case, a sequence of cards, and you’re using a small sequence of
the data to see if your prediction matches what comes later. Immediately you’re testing a feature of science
