Transcript Lecture01-ASTA01 - University of Toronto

ASTA01 – Intro to Astr. & Astrophys. I: the Sun and Planets
Introducing the lecturer:
Pawel Artymowicz (UofT)
• 5 years undergraduate
Physics+Astronomy program at Univ. of
Warsaw, Poland
• 4 years graduate study at the Space
Telescope Science Institute, Baltimore,
MD.
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ASTA01 – Intro to Ast. & Astroph. I: the sun and planets
Introducing the lecturer:
Pawel Artymowicz (UofT)
• 3 years postdoctoral NASA Hubble Fellow
at Univ. of California, Santa Cruz (UCSC),
USA
• 11 years senior researcher, asst. and
assoc. prof. in Stockholm University,
Sweden
• 8 years full tenured prof. UofT, Canada.
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ASTA01 – Intro to Ast. & Astroph. I: the sun and planets
Areas of expertise:
• Planetary system origins
Dusty disks like Beta Pictoris, dust avalanches,
dust disk instabilities
Migration of protoplanets in disks
Numerical hydrodynamics, GPU computing
• Binary stars
• Galactic dynamics, black holes and active
galactic nuclei
• Aerodynamics and aviation
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ASTA01 – Intro to Ast. & Astroph. I: the sun and planets
Where to look for course information:
syllabus, lecturer’s contact information
etc.
• Blackboard page of ASTA01
• Additional, linked course URL on
planets.utsc.utoronto.ca server of P.A.
• Your TA during and after tutorial
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ASTA01 – Intro to Ast. & Astroph. I: the sun and planets
Chapter 1
The Scale of the Cosmos:
Space and Time
• You are about to go on a voyage to the
limits of the known universe.
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• You will travel outward, away from your
home on Earth, past the moon and the sun
and the other planets of our solar system,
past the stars you see in the night sky, and
beyond billions more stars that can be
seen only with the aid of telescopes.
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• You will visit the most distant galaxies –
great globes and whirlpools of stars.
• Then, you will continue on, carried only by
experience and imagination, seeking to
understand the structure of the universe.
(that’s coming in ASTA02, next term!)
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• Astronomy is more than the study of
planets, stars, and galaxies.
• It is the study of the whole universe in which
you live.
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• Humanity is confined to a small planet
circling an average star.
• The study of astronomy can take you beyond
these boundaries and help you not only see
where you are in the universe, but understand
what you are.
• You will see how science works and how it
solves the oldest questions asked by
humankind, such as the existence of other
planets like our own, and other solar systems.
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• Your imagination is the key to discovery.
• It will be your scientific space-and-time
machine, transporting you across the universe
and into the past and future.
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• Although you will see evidence of a
beginning to the universe, you will not find
an edge or an end in space.
• No matter how far you voyage, you will not
run into a wall. The universe may be infinite.
• That is, it may extend in all directions without limit.
• About 90 years ago astronomers found that the
universe expands. About 13 years ago they found
that it is expanding at an accelerating pace.
Nobody yet knows exactly why.
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• Astronomy will introduce you to sizes,
distances, and times far beyond your
usual experience on Earth.
• Your task in this chapter is to grasp the
meaning, the scale, of these unfamiliar sizes,
distances, and times.
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• In this chapter, you
will compare objects
of different sizes in
order to comprehend
the scale of the
universe.
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From Solar System to Galaxy to Universe
• We can start very close to an interesting
object in the garden of the CERN visitor
centre.
• [Originally: Conseil Européen pour la
Recherche Nucléaire]
• CERN is the home of the Large Hadron
Collider, the largest particle accelerator in
operation today, which was designed to
simulate the beginning of the universe.
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From Solar System to Galaxy to Universe
• Bubble chambers were an important tool
for the study of particle physics from the
1950s to the 1980s, though they are now
most likely to be seen as museum
exhibits.
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From Solar System to Galaxy to Universe
• Not more than 100 metres under the
ground from the garden, massive
detectors are looking for the first signs of
the big bang, microscopic black holes,
dark matter.
• The results might shed light on many topics in
this book, and perhaps even change a few
chapters.
• We indeed live in exciting times!
• Physicists study collision of objects on the scale
< 0.000000000000001 m
= 1 fm (femtometer or fermi)
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From Solar System to Galaxy to Universe
• Our journey will start 10 metres from the
garden.
• Each view in the following sequence will be
made from a distance away that is 10 times
larger, until we come to such large distances
we will jump with higher increments.
From Solar System to Galaxy to Universe
• Every time you move 10 times away, your
field of view encompasses an area 10 x 10
larger than the previous square.
• Distances are first expressed as 1, 10, or 100
metres, until we come to such large distances
that a metre becomes too small as a unit.
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From Solar System to Galaxy to Universe
• We start using either prefixes (e.g., “kilo,”
which means “one thousand”) or scientific
notation (i.e., using powers of 10).
• For example:
•
•
•
•
•
•
•
101 = 10
102 = 10 * 10 = 100
103 = 10 * 10 * 10 = 1000 (kilo) ….
106 = 1,000,000 (mega)
109 = 1,000,000,000 (giga)
1012 = 1,000,000,000,000 (tera)
(…) peta, exa, ….
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From Solar System to Galaxy to Universe
• At a distance of 10 km, the image covers
about the same area as CERN’s Large
Hadron Collider (LHC).
From Solar System to Galaxy to Universe
• Ten times farther away, we can see Lake
Geneva and part of the Alps mountain
chain; 10 times farther again, we see
Switzerland and its neighbors, with a more
extensive view of the Alps.
• [can you spot errors in
illustrations in our textbook?]
From Solar System to Galaxy to Universe
• The Alps started forming 100 million years
ago when the African tectonic plate started
to move toward the European plate, and
the bottom of the sea rose to form new
mountains.
• The Alps still gain about one millimetre in
height every year, but since erosion is faster,
they will eventually round off and disappear.
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From Solar System to Galaxy to Universe
• Mountains and valleys are only temporary
features on Earth that are slowly but
constantly changing.
• As you explore the universe, you will come to
see that it, too, is always evolving.
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From Solar System to Galaxy to Universe
• In the next step of the journey, you will see
the entire planet Earth, which is about
13 000 kilometres in diameter.
• This picture shows most of the daylight side of
the planet.
• However, the blurriness at the
extreme right is the sunset line.
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From Solar System to Galaxy to Universe
• The rotation of Earth on its axis each 24
hours carries you eastward, and as you
cross the sunset line into darkness you
say that the Sun has set.
• At the scale of this figure,
the atmosphere on which
your life depends is thinner
than a strand of thread.
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From Solar System to Galaxy to Universe
• Enlarge your field of view again by a factor
of 100, and you see a region 1 000 000
kilometres wide.
• Earth is the small blue
dot in the centre,
and the Moon – with a
diameter only about 1/4
that of Earth
– is an even smaller dot
along its orbit.
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From Solar System to Galaxy to Universe
• If you’ve had a high-mileage car, it may
have travelled the equivalent of a trip to
the Moon.
• The average distance of the Moon from Earth
of 380 000 kilometres.
• These numbers are so large that it is inconvenient
to write them out.
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From Solar System to Galaxy to Universe
• Astronomy is the science of big numbers,
and you will use numbers much larger
than these to describe the universe.
• Here, we will jump to another measuring unit.
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From Solar System to Galaxy to Universe
• We enlarge a picture not 10 times or 100
times, but 150 times in order to fit a
specific distance into the picture, the
average distance from Earth to the Sun.
• This distance is called the Astronomical Unit
(AU). It is 1.5 * 108 km = 150 mln km =
= 1.5 * 1011 m.
• Introducing new units is another way astronomers
deal with large numbers.
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From Solar System to Galaxy to Universe
• Using the Astronomical Unit, you can then
say, for example, that
the average distance
from Venus to the Sun
0.7 AU
is about 0.7 AU.
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From Solar System to Galaxy to Universe
• The solar system consists of the Sun, its
family of planets, and some smaller
bodies, such as moons, asteroids, and
comets.
• Like Earth, Venus and Mercury are planets –
small, nonluminous bodies
that shine by reflecting
sunlight.
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From Solar System to Galaxy to Universe
• Venus is about the size of Earth, and
Mercury is a bit larger than Earth’s moon.
• In this figure they are both too small to be
seen as anything but tiny dots.
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From Solar System to Galaxy to Universe
• The Sun is a star, a self-luminous ball of
hot gas that generates its own energy.
• The Sun is about 110 times larger in diameter
than Earth, ~1.4 million km, but it, too, is
nothing more than a dot in the previous view.
• Earth orbits the Sun once a year.
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From Solar System to Galaxy to Universe
• Now we are jumping in increments of 100
times farther away than the previous view.
• Here you see the entire solar system, all the
major planets, and
their slightly elliptical
Scale: 100 AU
orbits.
• The details of the
Earth & Venus orbit are
lost in the red square
at the centre.
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From Solar System to Galaxy to Universe
• Light from the Sun reaches Earth in only 8
minutes, but it takes over 4 hours to reach
Neptune.
• Pluto orbits mostly
outside Neptune’s orbit,
but it is no longer
Scale: 100 AU
considered a major planet.
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From Solar System to Galaxy to Universe
• When you again move away
100 times farther, the solar
system becomes invisibly small.
• The Sun is only a point of light,
and all the planets and their
slightly elliptical orbits are now
crowded into the small red square
at the centre.
Scale: 10000 AU
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From Solar System to Galaxy to Universe
• The planets and the comets are too small
and reflect too little light to be visible so
near the brilliance of the Sun.
• Nor are any stars visible
except for the Sun.
Scale: 10000 AU
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From Solar System to Galaxy to Universe
• The Sun is a fairly typical star, a bit larger
than average, and it is located in a fairly
normal neighbourhood in the universe.
• Although there are many billions of stars like
the Sun, none is close enough to be visible in
the figure.
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From Solar System to Galaxy to Universe
• The stars are separated by average
distances about 30 times larger than this
view
Scale: 10000 AU
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From Solar System to Galaxy to Universe
• It is difficult to grasp the great isolation of
the stars.
• If the Sun were represented by a golf ball in
Toronto, the nearest star would be another
golf ball in Quebec City or Chicago.
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From Solar System to Galaxy to Universe
• In this figure, your view has expanded to a
diameter a bit over one million AU.
• The Sun is at the centre, and you see a few of
the nearest stars.
Scale: ~106 AU
• Symbol ~ means ‘of order’
Or ‘order of magnitude’
Or ‘roughly equal to’
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From Solar System to Galaxy to Universe
• These stars are so distant that it is not
reasonable to give their distances in AU.
• Astronomers have defined a new, larger unit
of distance – the light-year.
• One light-year (ly) is the
Scale: ~17 ly (lyr)
distance that light travels in
1 year,
~1013 km = 63 000 AU.
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From Solar System to Galaxy to Universe
• One of the nearest stars to the Sun,
Proxima Centauri, is 4.2 ly from Earth.
• In other words, light from
Proxima Centauri takes
4.2 years to reach us.
4.3 ly from us is a
companion Alpha Cen B.
An Earth-mass planet was
discovered 1yr ago around
it!
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From Solar System to Galaxy to Universe
• Although these stars are roughly the same
size as the Sun, they are so far away that
you cannot see them as anything but
points of light.
• Even with the largest single telescopes on
Earth, you still see only points of light when
you look at stars, and any planets that might
circle those stars are usually much too small
and faint to be visible [but there are
exceptions…]
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From Solar System to Galaxy to Universe
• Here the sizes of the dots represent not
the sizes of the stars but their brightness.
• This is the custom in astronomical diagrams,
and it is also how starlight is recorded.
• Bright stars make larger spots than faint stars
in a photograph or electronic picture.
• The size of a star image in a photograph tells you
not how big the star really is but only how bright it
looks.
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From Solar System to Galaxy to Universe
• Here, you expand your field of view by
another factor of 100, and the Sun and its
neighbouring stars vanish into the
background of thousands of stars.
• This figure has scale of 1700 ly in diameter.
From Solar System to Galaxy to Universe
• Of course, no one has ever journeyed
thousands of light-years from Earth to look
back and photograph the Sun’s
neighbourhood, so this is a representative
picture from Earth of a
part of the sky that can
be used as a reasonable
analogy.
From Solar System to Galaxy to Universe
• The Sun is faint enough that it would not
be easily located in a picture at this scale.
From Solar System to Galaxy to Universe
• Some things that are invisible in this figure
are actually critically important.
• You do not see the thin gas that fills the
spaces between the stars.
• Although these clouds of gas are thinner than the
best vacuum produced in laboratories on Earth, it
is these clouds that give birth to new stars.
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From Solar System to Galaxy to Universe
• The Sun formed from such a cloud about
4.56 billion years ago (4.56 Gy ago).
From Solar System to Galaxy to Universe
• If you expand your view again by a factor
of 100, you see our galaxy.
• A galaxy is a great cloud of stars, gas, and
dust bound together by the combined gravity
of all the matter.
From Solar System to Galaxy to Universe
• In the night sky, you see our galaxy from
the inside as a great, cloudy band of stars
ringing the sky as the Milky Way.
• Our galaxy is called the Milky Way Galaxy.
It has a small spindle-like
Structure in the center
called a galactic bar.
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From Solar System to Galaxy to Universe
• Our Sun would be invisible in such a
picture, but if you could see it, you would
find it about two thirds of the way from the
centre to the edge.
From Solar System to Galaxy to Universe
• Our Galaxy contains over 100 billion stars,
(1011 stars or 100 giga stars)
• like many others, it has graceful spiral arms
winding outward through the disk.
Beginning of Lecture 2
From Solar System to Galaxy to Universe
• Stars are born in great clouds of gas and
dust as they pass through the spiral arms.
• The disk of our galaxy is roughly 80 000 ly in
diameter.
Our Galaxy in infrared light, scale 80000 ly
From Solar System to Galaxy to Universe
• Only a century ago, astronomers thought
our Galaxy was the entire universe – an
island universe of stars in an otherwise
empty vastness.
• Now we know that the Milky Way Galaxy is
not unique; it is a typical galaxy in many
respects, although larger than most.
• In fact, ours is only one of a hundred
billions (1011 or 100 giga) galaxies
scattered throughout the observable
universe.
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From Solar System to Galaxy to Universe
• Other galaxies, for instance the nearby Large
Magellanic Cloud galaxy, also have star formation
regions!
Tarantula Nebula
in LMC
From Solar System to Galaxy to Universe
• As you move away 100 times farther, our
galaxy appears as a tiny luminous speck
surrounded by other specks.
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From Solar System to Galaxy to Universe
• This figure includes a region called Local
Group, 17 million ly in diameter, and each
of the dots represents a galaxy.
• Notice that our galaxy is part of a cluster of a
few dozen galaxies,
including Andromeda (M31)
Scale: 17 Mly
Scale: 0.1 Mly
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From Solar System to Galaxy to Universe
• Some of the galaxies have beautiful spiral patterns
like our own galaxy, but others do not.
• The general classification scheme of galaxies by
Edwin Hubble (who in 1920s observed the fact that
galaxies tend to move away from each other):
spiral, elliptical (smooth and without arms) or
irregular.
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A galaxy cluster held together by gravitation.
(galaxies are often found in clusters)
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From Solar System to Galaxy to Universe
• This picture represents a view with a diameter of
1.7 billion light years (100 x scale of Local Group)
From Solar System to Galaxy to Universe
• The figure shows clusters of galaxies
connected in a vast network.
• Clusters are grouped into superclusters –
clusters of clusters – and the
superclusters are linked to
form long filaments and walls
Scale: 1.7 Gly
outlining voids that seem
nearly empty of galaxies.
From Solar System to Galaxy to Universe
• These filaments and walls appear to be
the largest structures in the universe.
• If you could expand your view frame one
more time, you would probably see a uniform
fog of filaments and voids.
Scale: 1.7 Gly
From Solar System to Galaxy to Universe
• When you puzzle over the origin of these
structures, you are at the frontier of human
knowledge.
• [the textbook:] The sequence of figures
ends here because it has reached the
limits of the best telescopes.
• We have reached the cosmic horizon (time
since Big Bang * speed of light)
• Light travels only so far in the age of
universe… we’ll review available time
next.
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From Solar System to Galaxy to Universe
• Humanity’s view does not extend as far as the
region that would be covered by a figure 100
times larger than this picture.
This is about
the largest
Scale: 1.7 Gly
“Google Map” there is!
From Solar System to Galaxy to Universe
• Remember that each of the billions of
galaxies contains billions of stars.
• (~1011) x (~1011) = ~1022 stars =
= 10,000,000,000,000,000,000,000
• And that’s only in the observable Universe!
• 10% or more of those stars probably have
families of planets like our solar system, and
on some of those thousand billions of billions
of planets liquid-water oceans and protective
atmospheres may have sheltered the spark of
life. We don’t know on how many…
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ASTA01 – Introduction to Astr. & Astroph.1
We have already found thousands
of the so-called extrasolar planets
e.g.
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From Solar System to Galaxy to Universe
• It is possible that some other planets are
inhabited by intelligent creatures who
share your curiosity, wonder at the scale
of the cosmos, and are looking back at
you when you gaze into the heavens.
• We will talk about this possibility at the end
of this course.
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The Cosmic Calendar: Concepts of Time
• In the first part of chapter 1 you were
taken on a journey through the universe
from a spatial perspective to give you a
sense of the immensity of the universe
and how small our little corner of it really
is.
• Equally important is that you gain an
appreciation for the concept of time and how
the average human lifetime, for instance,
compares to the age of the universe.
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The Cosmic Calendar: Concepts of Time
• Our current understanding of the formation
of the universe and its age leads us to
believe that it has been about
13.7 billion years (13.7 Gy)
since the big bang, the instant the universe
commenced and, perhaps, the beginning
of time itself.
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The Cosmic Calendar: Concepts of Time
• Let’s imagine that the time our universe
has existed is spread over a one-year
calendar where each month is a little in
excess of one billion years – we have,
then, a cosmic calendar.
• The concept of the cosmic calendar was
devised by Carl Sagan, a well-known
astronomer at the end of the 20th century.
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The Cosmic Calendar: Concepts of Time
• As shown in the timeline on the next slide
(slide 71), the big bang occurred precisely
at midnight on January 1.
• The Milky Way Galaxy starts to coalesce in
late February or early March, which makes it
one of the oldest galaxies.
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The Cosmic Calendar: Concepts of Time
Big bang
Galaxy
The Cosmic Calendar: Concepts of Time
• Our solar system starts being built around
mid-August, and by the end of September
primitive life exists on Earth.
The Cosmic Calendar: Concepts of Time
• However, it is not until mid-December that
complex living structures such as
invertebrate life formed, and not until
December
25 when
dinosaurs
roamed
the Earth.
The Cosmic Calendar: Concepts of Time
• The end of the dinosaur era, which took place 65
million years ago, occurred yesterday, December
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The Cosmic Calendar: Concepts of Time
• The next day, December 31, is when all of
recorded history occurred and even then
not until much later in the day – within the
last 30
seconds,
in fact.
The Cosmic Calendar: Concepts of Time
• The Egyptian pyramids were built about 11
seconds ago.
• Copernicus convinces humanity that the Earth
orbits the Sun ~1 second ago.
• Erwin Schroedinger formulates his wave
equation of quantum mechanics and Edwin
Hubble observationally proves the expansion
of the universe about ~0.14 s ago
• Hubble Space Telescope goes into orbit (in
1990), ~0.05 seconds ago.
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The Cosmic Calendar: Concepts of Time
• You were born about 0.04 seconds ago
(assuming your age is 18).
• I started talking today ~2 microseconds (2
millionths of a second) ago.
• And it is now exactly midnight on
December 31 – Happy New Year!
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