1. Astronomy Unit 1 History of Astronomy Basic Concepts of Astronomy
Earth-Sun Relationship

2. History of Astronomy Vocab Words… Heliocentric Geocentric
Archaeoastronomy
Big Bang
Plasma Theory
Steady State Theory

3. History of Astronomy Where did “real” astronomy begin?
What did we know about astronomy 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”?

4. History of Astronomy Why were people interested in Astronomy?
Calendars
Planting/Farming depends on seasons
Religion & Astrology
Navigation
Timekeeping
Land Surveying

5. 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

6. 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.

7. 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: BC to 2000BC
Mesoamerican Site: BC to 1500 AD
Nazca Lines in Peru: 300 BC to 800 AD

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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 days, which is remarkably close to the modern value of days

14. 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

15. 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

16. History of Astronomy Aristarchus Mathematical Genius
Method of determing distance between sun, moon and earth

17. History of Astronomy
Aristarchus Measuring the Sun’s Size

18. 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

19. History of Astronomy
Eratosthenes Measurements

20. 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 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

21. 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

22. 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

23. 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

24. 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

25. Basic Concepts of Astronomy
Vocab Words
Light Year
Astronomical Unit
Constellation
Precession

26. 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

27. 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

28. 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
x 1015 km

29. 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.

30. 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

31. 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.

32. Basic Concepts of Astronomy
Precession of Earth….
Thuban
Vega (14,000 AD)

33. 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

34. 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.

35. 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 – days
A revolution is when an object travels around another object

36. Earth-Sun Relationship
The earth’s rotation is what gives us day and night

37. 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!

38. 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!

39. 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

40. 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

41. 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)
Northern Hemisphere it is around March 21st, Southern Hemisphere it is around September 21st

42. Earth-Sun Relationship

43. Earth-Sun Relationship
Apparent altitude of the sun