Scale of the Solar System Scale of the Universe

Scale of the Solar System
Scale of the Universe
•
•
•
•
•
How big is Earth compared to our solar system?
How far away are the stars?
How big is the Milky Way Galaxy?
How big is the Universe?
How do our lifetimes compare to the age of the Universe?
Sizes and Distances: How Big is Big?
• How big is the Earth compared to our solar system?
• On a scale of 1-to-10 billion, the Sun is about the size of a grapefruit.
The Earth is the size of a ball point about 15 m away. The distances
between planets are Huge compared to their sizes.
• How far away are the stars?
• Alpha Centauri is 4.4 light-years (or approx. 4.4x1013 km) away from us.
• On the same scale, the stars are thousands of km away.
Scale of 1:1010
Sizes and Distances: How Big is Big?
(Cont.)
• How big is the observable Universe?
•
•
•
•
• How big is the Milky Way Galaxy?
14 billion light-years in radius.
100 billion (or 1011) galaxies in the observable Universe.
100 billion stars per galaxy on average.
Total of 1022 stars in the observable Universe – as many stars as grains of
dry sand on all of the Earth’s beaches.
• There are about 1x1011 stars in the Milky Way Galaxy.
• It would take more than 3,000(!) years to count the stars in the Milky
Way Galaxy at a rate of one per second.
• The Milky Way Galaxy is about 100,000 light-years across; it takes light
100,000 years to travel across the galaxy!
How do our lifetimes compare to the
age of the Universe?
Cosmic Calendar: a time-scale on which we compress the
history of the Universe into one calendar year.
• Big Bang took place on Jan 1 at 00:00:00am.
• First galaxies were born in Feb.
• Solar System formed around Sep 3; early life in Earth formed
around Sep 22.
• Modern humans evolved on Dec 31 at 11:58pm.
• Our civilization is just a few seconds old! And a human lifetime is
a mere blink of an eye.
Spaceship Earth
•
•
•
•
How is Earth moving in our solar system?
How is our solar system moving in the Galaxy?
How do galaxies move within the Universe?
Are we ever sitting still?
1
How is Earth moving in our solar system?
• Contrary to our perception, we are not “sitting still.”
• We are moving with the Earth in several ways, and at
surprisingly fast speeds…
Earth orbits the Sun (revolves) once every year:
• at an average distance of 1 AU ≈ 150 million km.
• with Earth’s axis tilted by 23.5º (pointing to Polaris).
• and rotating in the same direction it orbits, counterclockwise as viewed from above the North Pole.
The Earth rotates
around its axis once
every day.
Our Sun moves randomly relative to the other stars
in the local Solar neighborhood…
• typical relative speeds of more than 70,000 km/hr.
• but stars are so far away that we cannot easily notice
their motion.
Are we ever sitting still?
… And the Sun orbits the galaxy every 230 million years.
•
How do galaxies move within the Universe?
Galaxies are carried along with the expansion of the Universe. But
how did Hubble figure out that the Universe is expanding?
Hubble discovered that:
• All galaxies outside our Local Group are
moving away from us.
• The more distant the galaxy, the faster it is
racing away.
Conclusion: We live in an expanding Universe!
2
How many stars are in the
observable Universe?
A.
B.
C.
D.
One hundred billion
1011
1022
1030
A.
B.
C.
D.
1022 stars are in the observable
Universe



There are about 100 billion galaxies in the
observable Universe.
That’s 1011 galaxies.
And there are roughly 100 billion stars in each
galaxy (some more, some less, but that’s about
the average). That’s 1011 stars per galaxy.
1011 stars
1011 galaxies x --------------1 galaxy
=
1.5 x 1013 cm
1.5 x 108 km
1 light year (1 ly)
1 astronomical unit (1 AU)
One hundred billion
1011
1022
1030
The Earth is 150 million kilometers
from the Sun. What is another way
of expressing this distance?
A.
B.
C.
D.
1.5 x 1013 cm
1.5 x 108 km
1 light year (1 ly)
1 astronomical unit (1 AU)
1022 stars
The Earth is 150 million kilometers
from the Sun. What is another way
of expressing this distance?
A.
B.
C.
D.
How many stars are in the
observable Universe?
1 AU, 1.5 x 108 km, 1.5 x 1013 cm
are all equivalent!
• An Astronomical Unit is DEFINED as the
distance from the Earth to the Sun
• For the others, write out 150 million km… that’s
150,000,000 km.
• Which is the same as 1.5 x 100,000,000 km…
therefore, 1.5 x 108 km
• To convert to centimeters:
103 m
102 cm
1.5 x 108 km x ---------- x ---------1 km
1m
= 1.5 x 1013 cm
3
How is Earth moving?
A. Rotates on its axis (spin).
B. Revolves around the Sun (orbit).
C. It doesn’t move.
Imagine the Sun has the diameter
of a grapefruit (14 cm). How large
would Jupiter be? (real diameters:
Sun - 1.4 x 106 km,
Jupiter - 1.4 x 105 km)
A.
B.
C.
D.
1.4 km
1.4 cm
1.4 x 1011 km
1.4 x 1030 km
1.4 cm (size of a marble)!



Notice that the Sun’s diameter is about 10 times
greater than Jupiter’s.
So, if our model Sun has a diameter of 14 cm,
divide that by ten…
1.4 cm
How is Earth moving?
A. Rotates on it’s axis (spin).
B. Revolves around the sun (orbit).
C. It doesn’t move.
Imagine the Sun has the diameter
of a grapefruit (14 cm). How large
would Jupiter be? (real diameters:
Sun - 1.4 x 106 km,
Jupiter - 1.4 x 105 km)
A.
B.
C.
D.
1.4 km
1.4 cm
1.4 x 1011 km
1.4 x 1030 km
Imagine the Sun has the diameter
of a grapefruit (14 cm). How far
away would Earth be? (real
distance: 1.5 x 108 km
Sun diameter: 1.4 x 106 km)
A.
B.
C.
D.
1500 cm
1500 m
15 cm
15 km
4
Imagine the Sun has the diameter
of a grapefruit (14 cm). How far
away would Earth be? (real
distance: 1.5 x 108 km
Sun diameter: 1.4 x 106 km)
A.
B.
C.
D.
1500 cm


Notice that the Earth-Sun distance is about 100 times
greater than the Sun’s diameter!
So, multiply the “grapefruit” Sun’s diameter by 100 to
find a model Earth-Sun distance of about 1400 cm, which
is close to the answer choice of 1500 cm.
1500 cm
1500 m
15 cm
15 km
History of Astronomy: Babylonians
and Greeks (pp. 52-61)
Ancient Roots of Science
• In what ways do all humans employ
scientific thinking?
• How did astronomical observations benefit
ancient societies?
• What did ancient civilizations achieve in
astronomy?
In what ways do all humans
employ scientific thinking?
•
•
•
Scientific thinking is based on everyday ideas of
observation and trial-and-error experiments…
Our goal is to explain and predict the observed
phenomena.
A scientific model is a conceptual representation that
provides both explanation and prediction of a given
phenomenon.
How did astronomical observations
benefit ancient societies?
• Keeping track of time and seasons
– for practical purposes, including
agriculture.
– for religious and ceremonial purposes.
• AND for aid in navigation
5
What did ancient civilizations
achieve in astronomy?
• daily timekeeping
•
•
•
•
•
•
tracking the seasons and calendar
monitoring lunar cycles
monitoring planets and stars
predicting eclipses
navigate
and more…
South Pacific: Polynesians were very skilled in the art of celestial navigation
Babylonia
Astronomy of Babylonians
• What were the purposes of Astronomy in
ancient Babylonia?
• What are the scientific breakthroughs of the
Babylonians?
• How did the western astronomy benefit
from these breakthroughs?
Purposes of Astronomy in ancient Babylonia
• As in most ancient cultures, astronomy was actually
practiced as astrology.
• Astronomical events, whether they were every-day
occurrences or rare incidents, had a deep religious meaning
for the people.
• It was believed that all things happened for a reason!
Lives were lived according to the advice of these
astronomers/astrologists!
• Orientation of the constellations was used to mark seasons
for harvesting or sowing crops.
• Certain constellations were noted for their yearly rising or setting
times, and provided an accurate clock by which time could be
measured.
Historically, two ethnic
groups, the Sumerians
and Akkadians, had
dominated the Babylonia.
An area rich in natural
resources, and
strategically located for
trade routes and
commerce, it was often
under threat from
outsiders throughout the
region's history.
The origins of western astronomy can be found in
Mesopotamia, the "land between the rivers" Tigris and
Euphrates.
What are the scientific breakthroughs of the
Babylonians?
• Babylonians not only recognized Venus as the same
object whether it appeared in the morning or evening, but
they actually developed a method for calculating the length
of the Venus cycle!
• Babylonians were able to predict solar and lunar eclipses.
They applied a simple method, which made future
predictions based on past observations!
• They almost certainly knew about the saros cycle; the general
pattern of eclipses repeats every 18 years (and 11.3 days).
• Babylonians created the zodiac–”the circle of little
animals”–which marked the twelve constellations that the
Sun, Moon, and planets travel between during their
movements through the sky.
6
What are the scientific breakthroughs of the
Babylonians? (Cont.)
• Constellations that we still use today, such as Leo,
Gemini, Capricorn, etc. were invented by the Sumerians
between 2,000-3,000 BC. A great deal of astronomical
mythology was handed down from the Sumerians.
• Babylonian system of mathematics was sexagesimal, or a
base 60 numeral system. From this we derive the modern
day usage of 60 seconds in a minute, and 60 minutes in an
hour.
• Babylonians invented the degree system to distinguish
positions in the sky (360 degrees, 60’ in 1 degree, etc.).
How did western astronomy benefit from
these breakthroughs?
• The Babylonian underpinnings of western astronomy are
extensive!
• It was from the Babylonians that the Greeks gained their
knowledge of the five visible planets and the constellations
of the zodiac, and centuries of recorded astronomical
observations.
• Greeks also adopted the idea that the motions of the
planets could be predicted with accuracy!
• Greeks adopted the degree system and also many of the
Babylonian constellations, which they renamed in Greek!
Ancient Greek Science
• Why does modern science trace its roots to
the Greeks?
• How did the Greeks explain planetary
motion?
• How did Islamic scientists preserve and
extend Greek science?
Why does modern science trace its roots to
the Greeks?
• Greeks were the first
Artist’s reconstruction of Library of Alexandria.
Established in 300 BC, this library existed for about 700
years!
What is a scientific model?
people known to make
models of nature.
• They used logic and
geometry to explain
patterns in nature without
resorting to myth or the
supernatural.
Greek geocentric model (400 BC)
• Scientific model is a conceptual
representation whose purpose is to explain
and predict observed phenomena.
• They sought to
understand the
architecture of the
Universe by constructing
models of nature.
7
How did Islamic scientists preserve and
extend Greek science?
How did Islamic scientists preserve and
extend Greek science? (Cont.)
• Muslim world preserved and enhanced the knowledge they
received from the Greeks (after the Library of Alexandria was
destroyed).
• While Europe was in its Dark Ages, Islamic scientists
preserved and extended Greek science, later helping to ignite
the European Renaissance.
• Al-Mamun’s House of Wisdom in Baghdad was a great
center of learning around 800 AD. Jews, Christians, and
Muslims worked in synergy to advance science.
More about the the European Renaissance at the next lecture!
• With the fall of Constantinople (Istanbul) in 1453 AD,
Eastern scholars headed west to Europe, carrying knowledge
that helped ignite the European Renaissance.
8