Transcript Astronomy Unit 1 - Mrs. Taylor's Class Page

Astronomy Unit 1
History of Astronomy
Basic Concepts of Astronomy
Earth-Sun Relationship
History of Astronomy
Vocab Words…
Heliocentric
Geocentric
Archaeoastronomy
Big Bang
Plasma Theory
Steady State Theory
History of Astronomy
 Where did “real” astronomy begin?
 What did we know about astronomy 2000+
years ago
 Who discovered some of the basic principles of
Astronomy – and how?
 What tools did they use back then?
 Why did they get into Astronomy?
 When were maps of sky created?
 When were constellations “invented”?
History of Astronomy
Why were people interested in
Astronomy?
Calendars
Planting/Farming depends on seasons
Religion & Astrology
Navigation
Timekeeping
Land Surveying
History of Astronomy
 Timelines:
Most of us think Astronomy really began with Galileo,
Copernicus, Brahe, etc.
Most of us think Astronomy really began with the use of
a telescope and modern technology.
Most facts about Astronomy were “known” thousands of
years ago without the sophisticated tools we have today
– but, they did use sophisticated reasoning and
mathematics
History of Astronomy
Archeoastronomy
The study of Ancient Astronomy in ancient
civilizations
We study ancient sites and ruins to determine what
these civilizations knew about astronomy
We don’t have record of who set up the ruins we
study today
We do know a little about what they knew by looking
at the ruins and studying the geometry and alignment
of these sites.
History of Astronomy
Some famous Archaeoastronomy Sites:
Nabta: Megalithic Site – 1000 years before
Stonehenge
Circles of stones marking solstices and cardinal
points more than 6000 years ago in Southern Egypt
Stonehenge: 3100 BC to 2000BC
Mesoamerican Site: 1500 BC to 1500 AD
Nazca Lines in Peru: 300 BC to 800 AD
History of Astronomy
Archaeoastronomy ended about 600 BC in
Greece
After archaeoastronomy, we had written
records of the events that occurred.
Not always 100% accurate, but
astronomers began writing out their
reasoning
History of Astronomy
 Who were the earliest Astronomers?
Thales of Miletus, Asia Minor
Pythagoras of Samos
Democritus of Abdera, Greece
Oenopides of Khios, Greece
Aristotle or Athens, Greece
Aristarchus of Samos
Eratosthenes of Cyrene, North Libya
Hipparchus of Rhodes
Ptolemy of Alexandria, Egypt
History of Astronomy
Thales: 624 to 547 BC
Said to have predicted a solar eclipse in 585
BC
Greeks already knew about the 19 year cycle
for lunar eclipses
Measured the height of the pyramids by
understanding “similar triangle” theory”:
Measure the shadow length at the time of day
when your shadow is as long as you are.
Developed early geometric theorems
History of Astronomy
Pythagoras: 580-500 BC
“Invented” some of the math that was needed to
get a scientific basis for astronomical
calculations – Pythagorean Theorem!!!!
First to note that the morning and evening stars
were both Venus
Built upon Anaximander’s ideas, who
postulated that planets and stars go around in
perfect circles.
Still believe geocentric model of universe
History of Astronomy
Democritus: 470 – 380 BC
Developed the concept of the atom: all things
were made of microscopic and indivisible,
indestructible atomic particles
He understood that the Milky Way was a large
collection of stars and also thought space was
limitless
History of Astronomy
 Oenopides: 450 BC
 Popularized the 12 signs of the Zodiac
 Probably copied them from the Assyrians in Mesopotamia
(Archaeoastronomy!!!!)
 First to fix the angle of the ecliptic with the celestial equator –
called it 24 degrees (Earth’s Tilt is actually 23 ½ degrees)
 Fixed the year to be 365 ¼ days long
 Postulated that the “Great Year” – the number of years when the
motion of the sun and the moon exactly repeated their motion –
was 59 years
 Oenopides result lead to a lunar month of 29.53013 days, which
is remarkably close to the modern value of 29.53059 days
History of Astronomy
 Aristotle: 384 – 322 BC
Did his best work on classifying plants and animals
Took a qualitative approach to science
Did not use mathematics in his studies
Earth, air, fire and water were the elements
Believed the earth was immobile (Geocentric)
Stars and planets use the Pythagoras circular spheres
model
Re-discovered in the late Middle Ages, and used to
impede observational science
History of Astronomy
Aristarchus: 310-230 BC
Believed in the Heliocentric Universe
Estimated the distance of the moon and sun
Utilized excellent mathematical principles but
lacked the tools to get the observational data
correct
All of his written records were destroyed in the
fire of the library in Alexandria
History of Astronomy
Aristarchus Mathematical Genius
Method of determing distance between sun,
moon and earth
History of Astronomy
Aristarchus Measuring the Sun’s Size
History of Astronomy
Eratosthenes: 276-197 BC
Developed a map of the world
Developed a way to find prime numbers
Estimated the circumference of the earth
Measured the tilt of the earth
Suggested that a leap day be added to the
calendar every 4th year
History of Astronomy
Eratosthenes Measurements
History of Astronomy
 Hipparchus: 190 – 120 BC
 Introduced the idea of 360 degrees in a circle
 Calculated the length of a year within 6.5 minutes
 Calculated the moon’s distance at between 59 & 67 radii –
correct answer is 60!
 Discovered precission – and calculated it at 46 seconds per
years – correct is 50.26 seconds per year
 Developed a star catalogue of 850 stars used later by Ptolemy
 Developed the currently used magnitude scale of 1 – 6
 Discovered the first nova
 Measured the distance to the moon using parallax
 Used different views of a solar eclipse
 Small angle formula
 Distance is about 240,000 miles
History of Astronomy
 Claudius Ptolemy: 85-165 AD
Developed the most sophisticated model of concentric
circles (epicycles) to determine planetary motion
He followed the geocentric theory
 The geocentric theory is the theory that the sun, planets
and all the other stars orbit around the earth. The earth is
at the center of the universe!
His Almagest had most of Aristotle’s ideas in it, with a
geocentric approach
Because it survived long periods of upheaval and wars,
it was “the” astronomy manual until the time of
Columbus
The History of Astronomy
 What did we know back then that was correct,
but “lost” (people didn’t believe it)….
The earth is round
Circumference/Diameter of the Earth
Distance to the Moon
The Solar System is Heliocentric
 The theory that the earth, along with the other planets
orbits the sun!
An estimate of the distance to the sun
Precision of the equinoxes
Length of the year to a high precision
The History of Astronomy
 The story does not end here…..
Most of what was known was lost again after this “high”
period of astronomy in Greece, Turkey and Egypt
Romans were not much interested in astronomy or
astrology
Arabs conquered many of these countries starting in the
7th century, and preserved a lot of the work done by the
ancients, refined it, and passed it back to the western
worlds at the end of Middle Ages
Thus it became the foundation of the work and ideas
that became prevalent in the 15th & 16th centuries
History of Astronomy
Many theories on the Origin of the
Universe
Big Bang
Steady State
Plasma
You can find info on each of the theories
within your reading booklets
Basic Concepts of Astronomy
Vocab Words
Light Year
Astronomical Unit
Constellation
Precession
Basic Concepts of Astronomy
Measuring Distances in Space
We use two major units when measuring
distances in space
Light Year & Astronomical Unit
Why don’t we use kilometers or miles?
Too small of a unit, it would be like measuring the
distance from here to your house in centimeters!
As we start studying larger and larger objects, we
even need larger scale units than Light Year &
Astronomical Units
Basic Concepts in Astronomy
Astronomical Unit
The average distance between the earth and
the sun
We measure distances within our solar system
(between planets or to the sun) with this unit
About equal to 149,598,000 km
Basic Concepts in Astronomy
Light Year
The distance light travels in one year
We measure distances outside our solar
system, but within our galaxy using this unit
About 9,460,528,400,000,000 km
9.4605284 x 1015 km
Basic Concepts of Astronomy
 A constellation is a group of stars that forms
some sort of figure when put together
 88 official constellations recognized by the
International Astronomical Union
 Thousands of years ago, they were names for
animals or mythological creatures
 Astronomers now use them to distinguish
different areas of the sky. For example, by
saying a planet is located in “Leo,” we know
what area of the sky to look in.
Basic Concepts of Astronomy
 88 recognized constellations can be found
behind your glossary in this booklet. Their
declination and right ascension is also listed,
along with meaning.
Asterisms are popular, unofficial names for these
constellations
Basic Concepts of Astronomy
 Precession of Earth
Currently Earth is tilted 23 ½ degrees, pointed right at
Polaris (The North Star)
Every 26,000 years the Earth’s axis traces out an
imaginary circle, very, very slowly!!!
During this shift, the tilt of Earth will go from pointing
directly at Polaris, to pointing at Vega and then pointing
at Thuban.
The motion of Earth’s axis is called Precession
This is the reason your astrological signs do not
necessarily match up with the rising at setting of the
constellations anymore.
Basic Concepts of Astronomy
Precession of Earth….
Thuban
Vega
(14,000 AD)
Earth-Sun Relationship
 Vocab Words
 Rotation
 Revolution
 Terrestrial Globe
 Latitude
 Longitude
 Tropic of Cancer
 Tropic of Capricorn
 Equator
 Prime Meridian
 Autumnal Equinox
 Vernal Equinox
 Winter Solstice
 Summer Solstice
Earth-Sun Relationship
 Terrestrial Globe is the spherical
representation of the earth.
The imaginary line that separates the
earth into a Northern and Southern
hemisphere is the equator.
The imaginary line that separates the
earth into a an Easter and Western
hemisphere is the Prime Meridian.
Latitude measures distances North
and South of the equator.
Longitude measures distances East
and West of the Prime Meridian.
Earth-Sun Relationship
Earth is constantly moving in two ways…
It is taking one rotation around itself each day
A rotation is when an object spins around itself
It is taking one revolution around the sun each
year – 365.25 days
A revolution is when an object travels around another
object
Earth-Sun Relationship
The earth’s rotation is what gives us day
and night
Earth-Sun Relationship
Earth’s revolution is what gives us
seasons, but only because the EARTH IS
TILTED AT 23 ½ DEGREES!!!!
Earth is closest to the sun in its revolution
in December and furthest in its revolution
in June!
Earth-Sun Relationship
Sun appears to shine directly in different
locations throughout the year.
Goes from shining at the equator to
shining at the Tropic of Cancer, back to the
equator, down to the Tropic of Capricorn
and then back to the equator
Repeats this cycle over and over again!
Earth-Sun Relationship
 Tropic of Cancer is 23 ½ degrees North latitude
Furthest north the sun appears to shine directly!
Shines here around June 21st
 Tropic of Capricorn is 23 ½ degrees South
latitude
Furthest south the sun appears to shine directly!
Shines here around December 21st
Earth-Sun Relationship
 Summer Solstice
 First day of Summer
 The day your hemisphere is tilted directly towards the sun
 Longest day of the year
 Northern Hemisphere it is around June 21st, Southern
Hemisphere it is around December 21st
 Winter Solstice
 First day of Winter
 The day your hemisphere is tilted directly away from the sun
 Shortest day of the year
 Northern Hemisphere it is around December 21st, Southern
Hemisphere is it around June 21st
Earth-Sun Relationship
 Autumnal Equinox
 First day of Fall
 The day the sun is shining directly at the equator, but moving
away from the hemisphere you are living in (towards winter)
 12 hours of daylight, 12 hours of darkness
 Northern Hemisphere it is around September 21st, Southern
Hemisphere it is around March 21st
 Vernal Equinox
 First day of Spring
 The day the sun is shining directly at the equator, but moving
toward the hemisphere you are living in (towards summer)
 12 hours of daylight, 12 hours of darkness
 Northern Hemisphere it is around March 21st, Southern
Hemisphere it is around September 21st
Earth-Sun Relationship
Earth-Sun Relationship
Apparent altitude of the sun