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) 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