A Brief history of astronomy Important Figures and Advancements

Ancient civilizations and the stars All of the ancient and earliest of human cultures studied the stars and recognized their significance. Most civilizations believed the stars to be of divine origin and created religions around them. They integrated this knowledge of the stars into many aspects of their daily functioning, such as: Creating calendars based on the movements of the sun and moon, and the position of the stars. Predicting seasonal events such as rain, drought, seasons and tides, as well as when optimum planting and harvesting times were. Charting star positions in order to navigate the land or sea as they travelled across the globe. Ancient civilizations and the stars

Egypt Constellations, (groupings of stars), were worshiped as gods. Temples, pyramids, etc. were built in relation to the position of objects in space. North/South was determined by the rising and setting of stars. Astronomers in Egypt were very powerful: they could make predictions based on constellations. The rising of the “dog star” Sirius just before sunrise signaled the Nile River Floods. Egyptians based their seasons around this event. Egypt

Predicted comets and eclipses by keeping track of events over time. Developed a very accurate calendar; used it effectively for agriculture, (when to plant, grow, harvest, etc.) Developed a table charting the position of the moon and the planets at the same time as the Greeks. China

Mayans Kept very accurate time without tools – purely observations. Brightest object in the sky, (besides sun and moon) = Venus. Mayan’s worshiped all three of these celestial bodies. Like Egyptians – built buildings and temples to face these objects on certain days. Created a very accurate, (and famous), calendar based on the rising, setting and positions of the sun, moon and Venus, as well as solar/lunar eclipses. Believed the Earth was flat with 4 corners represented by North, South, East and West. Mayans

Stonehenge ????? Construction must have begun around 3000 b.c. Not certain whether it is actually finished or not. Main stones are positioned to line up with the sun rising on the longest day of the year. Stones were continuously added to it over many hundreds of years – meaning of the structure changed over time. Stonehenge

Greece: Aristotle’s universe Aristotle first proposed the idea of the: Geocentric Universe Geo = Earth The geocentric universe is the theory that the Earth is the center of the universe and all other celestial bodies orbit around the Earth. First proposed by Aristotle in ancient Greece. All observations – did not have telescopes. Greece: Aristotle’s universe

Predict!! When do you think humans first discovered that the earth was not flat? Around what time period do you think humans first discovered that the Earth was, in fact, round? Said another way: how long did humans believe the false idea that the Earth was flat?

Answer: Around 273 B.C.!!

Greek astronomer and mathematician who lived in Egypt: ran the famous Egyptian library at Alexandria. Lived around 273 B.C. First man to discover that the Earth was round using trigonometry. Used large sticks in the ground to create shadows. Used angles of shadows and distances between poles to calculate the circumference, (distance around), of the Earth. Eratosthenes

Eratosthenes Cont.: How did he do it?? Eratosthenes knew of a famous well in Egypt where, on the summer solstice, the sun shined down directly into the well, (looking down into the well, no shadows created on water). He put up large poles in Alexandria, (a good distance away from the town with this well), and measured the angle of the shadow created by the sun on the same day. Because the sun shined down directly over this well but not over Alexandria, (hence the shadows), he knew the Earth could not be flat. Using the angles of the shadows he found from his poles, and the knowledge of the distance between the well and the poles, he used trigonometry to calculate the circumference of the Earth. Eratosthenes Cont.: How did he do it??

Claudius Ptolomeus (Ptolomy) Roman citizen, 90-160 A.D. Formally wrote down and published the geocentric theory, with the Earth as a non-moving object at the center of the universe. In his publication, he created a model called “epicycles” to explain the variations in speed, orbits and motions of some of the various objects observed in the sky that did not fit the geocentric model. (We now know that these ‘strange’ motions were planets that were not orbiting Earth at all, but instead the sun). His geocentric model was widely accepted for almost 1400 years. Claudius Ptolomeus (Ptolomy)

Copernicus 1473-1543 The founder of modern astronomy. First to propose that the Earth was spinning. Said that this could explain the strange motions of some celestial objects that Ptolemy tried to describe with his ‘epicycles’ Also the first to believe that the earth was revolving around the sun, rather than being the center of the universe. Was afraid to announce this theory for fear of the ramifications with the Church. Copernicus

1546-1601 Refuted Ptolemy’s model of the solar system and created a new model. In Brahe’s model, the Earth was still the center, (geocentrism), but the planets and other celestial objects orbited the sun rather than the Earth. First to observe a supernova in 1572 Tyco Brahe

Johannes Kepler 1571-1631: Brahe’s assistant Developed the three laws of planetary motion still used today. Every planet orbits in an ellipse around the sun. Every planet sweeps out an equal amount of area in an equal amount of time during it’s orbit. Close planets orbit the sun faster than farther planets. Johannes Kepler

Galileo: 1564-1642, Italy One of the most famous figures in astronomy Built his own ‘refracting’ telescope. Used it to observe the heavens. Through his many observations, he compiled evidence that the heavens were moving. Jupiter’s 4 large moons, moving around Jupiter. Sunspots Venus has phases, just like our moon Craters on the moon All of the evidence he compiled led him to one logical conclusion: the Earth and all the planets revolve around the sun. Galileo: 1564-1642, Italy

Galileo, continued Heliocentric Universe Helios = Greek god of the sun. Helio = sun The heliocentric universe is the idea that the Earth and all of the planets revolve around the sun. First developed by Copernicus, formally announced with evidence by Galileo. Galileo, continued

1633: Wrote a book titled Dialogue Concerning the Two Chief World Systems In the book, he has two people having a discussion, one arguing for geocentrism, (Ptolemy) and one arguing for heliocentrism, (Copernicus). The book presents all of his evidence proving the heliocentric universe. Galileo gets into conflict with the Church over his claims and is placed under house arrest for much of the rest of his life. Galileo, Cont.

Sir Isaac newton Also well known for developing his laws of motion: Inertia, (objects at rest stay at rest, objects in motion stay in motion). Force equals mass times acceleration, (F = MA) Action – Reaction 1643-1727, England Mathematician, Physicist, Philosopher. Remodeled Galileo's design of the telescope using mirrors. Created the law of universal gravitation which is still applied to planetary motion and gravity today. Created the field of calculus in order to solve some of his own problems. Sir Isaac newton

Modern Astronomical advancements Many more modern advancements have been made in the field of astronomy. Some important advancements include: The space program: orbiting the Earth, landing on the moon, the international space station. The Hubble Space Telescope: 1990. Satellite telescope placed in space. Above the atmosphere, clouds, etc., it has an unobstructed view of the universe. Probes into space: Mars Rover, Juno, (recent probe to Jupiter), Voyager, etc. Modern Astronomical advancements