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

Astronomy Unit 1

History of Astronomy

Basic Concepts of Astronomy

Earth-Sun Relationship


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


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”?


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


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


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.


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


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


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


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


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


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


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


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


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


Aristarchus Mathematical Genius Method of determing distance between sun,

moon and earth


Aristarchus Measuring the Sun’s Size


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


Eratosthenes Measurements


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


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


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


Vocab Words Light Year Astronomical Unit Constellation Precession


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


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.


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


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.


Precession of Earth….

ThubanVega (14,000 AD)


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


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 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


The earth’s rotation is what gives us day and night


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!


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!


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


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


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



Apparent altitude of the sun

Documents

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