Astronomy Unit 1

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Astronomy Unit 1

• History of Astronomy
• Basic Concepts of Astronomy
• Earth-Sun Relationship

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History of Astronomy

• Vocab Words
• Heliocentric
• Geocentric
• Archaeoastronomy
• Big Bang
• Plasma Theory
• Steady State Theory

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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?

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History of Astronomy

• Why were people interested in Astronomy?
• Calendars
• Planting/Farming depends on seasons
• Religion Astrology
• Navigation
• Timekeeping
• Land Surveying

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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

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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 dont 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.

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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

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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

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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

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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

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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 Anaximanders ideas, who postulated
  that planets and stars go around in perfect
  circles.
• Still believe geocentric model of universe

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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

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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 (Earths
  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

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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

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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

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History of Astronomy

• Aristarchus Mathematical Genius
• Method of determing distance between sun, moon
  and earth

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History of Astronomy

• Aristarchus Measuring the Suns Size

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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

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History of Astronomy

• Eratosthenes Measurements

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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 moons 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

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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 Aristotles 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

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The History of Astronomy

• What did we know back then that was correct, but
  lost (people didnt 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

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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

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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

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Basic Concepts of Astronomy

• Vocab Words
• Light Year
• Astronomical Unit
• Constellation
• Precession

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Basic Concepts of Astronomy

• Measuring Distances in Space
• We use two major units when measuring distances
  in space
• Light Year Astronomical Unit
• Why dont 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

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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

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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

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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.

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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

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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 Earths 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 Earths 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.

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Basic Concepts of Astronomy

• Precession of Earth.

Thuban
Vega (14,000 AD)
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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

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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.

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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

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Earth-Sun Relationship

• The earths rotation is what gives us day and
  night

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Earth-Sun Relationship

• Earths 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!

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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!

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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

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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

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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

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Earth-Sun Relationship
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Earth-Sun Relationship

• Apparent altitude of the sun