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Distance and Time Presentation
Slide 1
Astronomers and virtually all other scientists are in agreement that our universe had a
beginning in time. The exact date for the beginning of time, often called the big bang, is
still being debated, but the majority of indicators point to dates between 12 and 13 billion
years ago. Here we will use a date for the big bang of 12.5 billion years ago. To give
you some idea of how long a time span this is, let’s represent 12.5 billion years as one
calendar year. Thus each month represents a bit more than a billion years, each day
represents about 34 million years, each hour 1.4 million years, and each minute 23
thousand years. One this scale, modern humans first appeared about 6 minutes before
midnight on the last day of the year, and the first cities arose about 20 seconds before
midnight.
Slide 2
Clearly, humans and modern technology are very recent arrivals on the universal scene.
Since the Earth has been around for about 4.5 billion years, it seems that it took a very
long time for our debut. To understand this time frame, consider that the Earth’s
formation from the accretion of massive debris continued till about 3.8 billion years ago,
in the form of bombardment by asteroid and comet like objects up to 100 km in diameter.
When this accretion era ended, life was able to gain a toehold on planet Earth and never
let go. Surprisingly, within a few million years of the last Ocean evaporating and crust
melting collision, single celled organisms were proliferating in warm shallow oceans, and
possibly near deep sea thermal vents. Stromatilites, shown here in Western Australia, are
fossil remains of these early organisms.
Slide 3.
Here you can see a time line for the evidence of life on Earth. Note that this timeline ends
when multi-cellular life is well established, some 500 million years ago in the Cambrian
period.
Slide 4.
. Another big surprise, however, is that muli-cellular organisms didn’t evolve until
somewhere between a billion and 800 million years ago..A gap of nearly three billion
years! What took so long? Our current and best theory is relatively simple: cellular and
especially multi-cellular life required certain atmospheric considtions..the buildup of
oxygen for example. Since Oxygen was produced by the earliest life forms as a waste
gas, it took a very long time for atmospheric oxygen to build up to high enough levels. A
tremendous period of evolutionary growth took place some 500 million years ago, called
the Cambrian Explosion, from which the current forms of life of earth have diverged.
Clearly, however, the Cambrian period was preceded by an earlier period of multicellular life, often called the Precambrian, some 600 to 700 million years ago.
Slide 5
Before we get too far a field from our study of Astronomy, it is worth pausing to note that
life was we know it on Earth may only be the survivors….Life may have arose several
times during the first billion years of the Earth’s history, only to be snuffed out by ;planet
Sterilizing impacts. Many scientists theorize that the impacts themselves may have
seeded the Earth with the necessary ingredients, if not the life forms themselves, to begin
that long road to people, platypuses, puppy dogs, and Redwood trees that are now so
familiar. If you are interested and have time, please check out the website listed here.
Slide 6:
While we are on the subject of time, consider that not all stars and planets were born at
the same time as our sun and Earth. With over 12 billion years of possibilities, it is a
definitely likelihood that some stars and earth-like planets got their star millions or even a
billion or two years ahead of us. Thus intelligent beings could have quite a head start on
humanity. Would technology be like in a thousand years on Earth? What would
technology be like for intelligent beings with a billion year head start..its boggles the
mind…Also consider that the longer a civilization has been around, the more likely it is
that their star is aging and that they are in need of a new home…Can they just zip on
over to Earth? Have they done so already? Although we can’t really answer this
question to everyone’s satisfaction, we can get some insight by considering the distances
involved between the stars.
Slide 7.
First of all, consider that everything you see, especially in space is an image that has been
traveling to us at the speed of light….when you look at the sun, your eyes (or a camera)
are intercepting photons of light that left the sun eight minutes earlier. Light from the
stars, takes years to travel the distance to earth, even at the speed of light, some 186,000
miles per second. Light from the brightest star, Sirius takes 8 years to get to Earth. The
beautiful images of the Orion Nebula, shown here, show an object as it was some 1400
years ago when the light that is now reaching us was emitted. Continuing to the limits of
time, the most distant objects visible are about 12 billion light years away, since light
from those objects left soon after our universe began. Light from more distant objects is
beyond the cosmic horizon and hasn’t yet reached us!
Slide 8.
Here is an image of the nearest large Galaxy of Stars, M31, the Andromeda Galaxy, some
two million light years away. If Astronomers on that Galaxy could view objects as small
as people on Earth, they would see australopithecines rather than people…the three foot
tall ape like precursors of modern humans.
Slide 9.
Here you can see a meteor shower—bits of comet dust striking the earth at high speed as
we pass through the tail of a long gone comet. The Milky Way is visible in the
background.
Slide 10.
If our sun was scaled down to the size of a grapefruit was placed at one end of the giant
air and space museum in Washington DC, the scaled down planet Uranus would be
orbiting near the opposite end of the building. Where would the nearest star, also the size
of a grapefruit, be on this scale?
Slide 11
You’ll have to zoom way out to see it. the next nearest star, Alpha Centauri, would be
located 5000 km way…San Francisco would be the right distance.
Slide 12
Given the immense distances between stars, if is sobering to realize that the Sun and
alpha centauri appear right next to one another in an image of the Milky Way Galaxy.
For comparison, this distance between stars is about 4 light years, while the distance from
the Sun to the center of the Milky Way is about 30,000 light years.
Slide 13.
To compare galaxies and the space between them, we have to drastically change scales.
Now let’s let the galaxies be the size of grapefruits, or more realistically, compacts disks
with a golf ball stuck in the middle to represent the nucleus. If the Milky Way was one
compact disk, how far away would the next large galaxy, M31 be? The answer is about 2
meters, or about 20 compact disk diameters away. The actual distance between them is
2.2 million light years.
Slide 14
So we live on the Earth, orbit the sun, and the sun orbits around within the Milky Way
galaxy. Are there other groupings to which we belong? In other words, what is our
correct universal address? Lets start with our address, city, state, Country, and Planet
Earth…of course some addresses are at less fortunate at times than others…note
Hurricane Katrina in this image bearing down on new Orleans…
Slide 15
The next line on our universal address is the solar system, which we share with a large
family of planets..a few of which are shown here next to the moon at sunset.
Slide 16
After solar system, we would write Milky Way galaxy, though Aliens around another star
might be interested in which part of the vast galaxy. Specify, “outer Orion Arm” might
help, though they would have a different name for the constellation in that direction.
Perhaps saying we are 30,000 light years from the center might help a bit.
Slide 17
After Milky Way, the next line in our address is “Local Group” of galaxies, meaning that
the Milky Way is part of some 30 other galaxies all gravitationally bound together in a
region some 3 million light years in diameter.
Slide 18
The next line in our rather long address is “local super cluster” or perhaps the Virgo
Super cluster, since this 50 million light year spheroid of galaxies is dominated by the
Virgo cluster, with thousands of Galaxies in its own right.
Slide 19
The last line may be unnecessary, but until we learn otherwise its best to write Universe
at the end. There don’t appear to be groupings of super clusters, so at the largest scale,
the universe is made of super clusters and Voids between them. To see a tour of the
universe at large and small scales, check out the website shown here.
Slide 20
Time to take a brief quiz to test your knowledge of distance and time. First question;
How many kilometers in a Mile?
Slide 21:
The Answer is:
1.6 or 10/6. in other words, 6 miles is the same as ten kilometers.
Slide 22
Next questions: how many kilometers in diameter is the Earth?
Slide 23:
Answer; 12,700 km
Note that you can convert this to miles by multiplying by 6/10 to get 7,900 miles.
Slide 24
How far away is the moon
Slide 25
The answer is 384,000 km . In scientific notation, you can write this as 3.84 x 105 km.
Slide 26
Since that is a rather large and abstract number is it earlier to remember the distance to
the moon in terms of the diameter of the earth. How many Earth diameters away is the
moon?
Slide 27
The answer is about 30 earth diameters. That means that if you represent the earth by a
classroom globe one foot in diameter, the moons distance would be about 30 feet.
Slide 28
Compared with the distanced to the moon, how much farther away is the sun?
The answer is about 400 times farther. In fact the sun is both 400 times larger and 400
times farther away.
So how long does it take light to get from the sun to the earth?
The answer is about 8 light minutes…
Slide 29
• How many Light minutes to Jupiter?
5 AU x 8 minutes/AU = 40 minutes
• How many AU to Neptune?
30
• How many AU in one light year?
65000
• How many light years to the NEAREST star?
4
Slide 30
• How many light years away is the farthest star we can see with our naked eyes?
Slide 31
About 3000 light years (Deneb in the constellation Cygnus is quite bright at a
distance of 2200 light years
Slide 31
How far to the Center of Galaxy
Slide 32
a 30,000 light years. Note that astronomers also using another large unit of distance,
the parsec. One parsec is 3.26 light years, so the center of the galaxy is a bit less than
ten thousand parsecs, or ten kiloparsecs away.
Slide 33
How far to the Andromeda Galaxy?
Slide 34
• Two million light years
• Remember—about twenty times the diameter of the Milky Way
Slide 35
Last question: How far is it to the edge of the observable universe?
Slide 36
• 12 billion light years!
• But what is the observable universe?
• It’s a sphere with a radius equal to the age of the universe in light years.
• If something is farther away than this, then light hasn’t reached yet, so we can’t
see it!
Slide 38
Before we leave the concept of distance and time, its worth exploring the concept of
motion as well, as space, time, and motion are intrinsically linked together.
•
•
•
Contrary to our perception, we are not “sitting still.”
We are on a spinning, orbiting planet, about a star which is orbiting the Milky
Way Galaxy, which itself is moving outwards as park of the expansion of the
Universe!
Lets start with the spin…the floor beneath your feet is moving eastward with the
rest of the earth at about 1500 km/hr or 2200 feet per second. If you jump in the
air for half a second and manage to not move with the earth below you, then you
will land about one thousand feet west of where you jumped…thank gravity and
inertia that you don’t!
Slide 39
The earth is moving about the sun considerably faster, however. In one year, the
earth travels in a one billion kilometer circle, so dividing one billion kilometers by the
number of seconds in a year (31 million) gives a speed of about 30 km/s. If you
jumped off the earth and could hover in space, your spot on the earth would be 30 km
away before you could blink twice!
Slide 40
Like all stars, the sun is orbiting the center of the milky way…it takes 250 million
years to make an orbit with a radius of 30,000 light years. This works out to about 40
km/s…before you get dizzy, remember that we aren’t orbiting the sun and the Milky
way in the same direction! Okay, I guess that doesn’t help.
Slide 41
Finally, the Milky Way is moving away from the other galaxies as part of the
expansion of space time, which began with the big bang. There is no one speed
here…all the galaxies are moving apart from one another at speeds that depend on
their distance…in fact, they aren’t moving through space at all…space itself is
expanding, carrying the galaxies with them!
Slide 42
Time to slow down for minute…in fact we’ve come to the end of this presentation.
Still, we have no choice but to continue our journey through time and space. Like
people, stars are moving through time towards a violent end…..the sun is one such
star. Within the next four billion years, the sun will swell like the nebula shown here,
boiling the oceans and making the earth uninhabitable for life as we know it. Will we
still be around to watch and perhaps do something about it? Will any life forms have
the technology to reverse the sun’s evolution, or set out for new home? For now, our
best hope is to study the stars and planets for clues to the solution to this ultimate
puzzle. Welcome to Astronomy!