Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Astronomy • Oldest “Science” • Observed patterns and regularities between events on Earth and the position of heavenly bodies – recorded data about the heavenly bodies started with earliest written records • Could use patterns to make predictions – What sort of observed patterns could lead to useful predictions? • seasons and position of the sun • Equinoxes, length of days Greek Astronomy (600 BC- AD 150) • Much of their arguments were non-science. • Used geometry and trigonometry to measure sizes and distances of sun and moon. • Geocentric (Earth Centered). – Phases of the moon understood if moon is a sphere shining with reflected light – Eclipses understood if Moon passes by Earth’s shadow – Spherical Earth understood • Earth cast curved shadow during lunar eclipse – Heavens misunderstood • Rotating celestial sphere. Greek Astronomy (600 BC- AD 150) • Found circumference of the Earth. – Used difference in the angles of sun’s shadow at two locations, distance between the locations, and assumption of spherical Earth. • • • • • Only one cast a shadow Angle = 7 degrees (1/50 of a circle). D = 31726 km between cities 50 x 31726 km= 39,400 km for the whole circle. (actual Earth circumference = 40,075 km). Greek Astronomy (600 BC- AD 150) • • • • • Only one cast a shadow. 7 degrees = (1/50 of a circle). 5000 stadia (1 stadia /0.1576 km) = 31726 km. 50 x 31726 km= 39,400 km for the whole circle. (actual = 40,075 km). Greek Astronomy (600 BC- AD 150) • Heliocentric (Sun Centered). – Suggested 200 BC, but didn’t catch on • indirect measurement was used to calculate size of Sun and Moon. • Found the Sun is much larger than the Earth, much farther away than the Moon. • If Sun is so much bigger, and farther away, wouldn’t it make sense that the Earth would revolve around it, rather than vice versa? Greek Astronomy (600 BC- AD 150) • Ptolemaic System (Geocentric). – The most generally accepted theory – All heavenly bodies revolve around Earth – Accounted for retrograde motion by Spirograph method – Similar to passing a car Modern Astronomy : Authors • Nicholas Copernicus (1473-1543). Heliocentric. – First “modern” astronomer to be proponent of the heliocentric model – Earth is a planet, therefore should behave like other planets. Doesn’t make sense it is the center. – Used circular orbits, which still didn’t quite fit observations. – Work was published on is deathbed, so he didn’t suffer the consequences of social ostracism. Modern Astronomy: Authors • Tycho Brahe (1546-1601) Geocentric – Headed a Danish observatory. – Very precise measurements of Mars and other heavenly bodies. – Not heliocentric because he didn’t see stellar parallax – Change in position of stars relative to Earth’s position in revolving around the sun – Like closing one eye and pointing to a distant object, then switching eyes without moving your finger. Modern Astronomy: Authors • Johannes Kepler (1571-1630) Heliocentric. – Tycho’s assistant. • Used Tycho’s data to prove heliocentric model better. • Mars orbit is elliptical. – 3 Laws of Planetary Motion. • Path of each planet is an ellipse with the Sun as one focus. • Revolution carves out equal areas in equal amount of time. • Orbital periods of the planets and their distances from the Sun are proportional (p2=d3). – Did not determine the forces that produce the planetary motion. Modern Astronomy: Authors • Galileo Galilei (1564-1642) Heliocentric. – First to make and use telescopes in astronomy. • Found 4 moons orbiting Jupiter. – Therefore Earth not the center of revolution for everything! And moons not left behind as Jupiter revolved around the Sun. • Planets are circular discs, not points of light. • Venus has phases, like the Moon, so the sun is the center of it’s revolution. – Venus is smallest in full phase. • Moons surface has landforms. • Sun has sunspots, and it rotates. – Tried by the Inquisition, convicted, imprisoned, became blind. Modern Astronomy: Authors • Sir Isaac Newton (1642-1727). – Universal Law of Gravitation • Every body attracts every other body with a force proportional to their masses and inversely proportional to the square of the distances between them. – 3 Laws of Motion • Inertia: An object in motion continues moving at uniform speed in a straight line unless an outside force acts on it • F=ma • Every force (action) has and equal and opposite force (reaction) Gravity • Gravity increases with increasing mass • Gravity decreases with distance • Fg = G m1m2/d2 • Where G=6.67x10-11 Nm2/kg2 • (Small enough to ignore) Mass and Weight • MASS is how much matter an object has – how many atoms and what kind of atoms • some atoms have more mass because they have more protons and neutrons – Mass doesn’t change from one place to another • WEIGHT is the acceleration due to gravity acting on a mass – Weight is actually a force (F=ma; mass being accelerated) – Gravity will differ based on the mass of the planet, so weight can change. You can be “weightless”, but not “massless”