1. Alta High Astronomy Chapter 2 The History of Astronomy

2. Einstein Einstein improved upon the work of Newton by explaining how gravity worked! The Universe is actually made up of a 4 dimensional fabric we call the space- time continuum. Gravity is the effect of heavy massive objects bending or warping that fabric. Gravity travels at the speed of light 3 x 10 ^8 m/s (186000 mph) Alta High Astronomy

3. The Ancient Astronomers Most Ancient Astronomy revolved around agriculture  Most famous astronomical construct – Stonehenge on the Salisbury Plain of England Used as a calendar  Other Examples Big Horn Medicine Wheel in Wyoming Caracol Temple on the Yucatan Peninsula

4. Alta High Astronomy The Greeks and Muslim Astronomers Muslim Astronomers Created trigonometry and Algebra – they were the first mathematicians Greeks – continued their work and developed the first models of the Universe

5. Alta High Astronomy The Greeks The Sun, Moon, and Planets were the known Universe  Sun, Moon and Stars were fixed on the Celestial Sphere  Planetes – wanderers planets move both east to west and appear to move west to east Apparent west to east motion is called retrograde motion.  Aristotle -The Universe is Geocentric – Everything revolves around the earth and everything moves in a circle.

6. Alta High Astronomy Ptolemy 140 AD – Ptolemy constructed the best Geocentric model In order for the model to fit the data it required the use of epicycles.  Epicycles or a circle on a circle – required over 80 circles The main circle around the earth is called the deferent and the circle on that circle is called the epicycle

7. Alta High Astronomy Copernicus 16 th Century – Nicholas Copernicus rediscovered the early Greek work by Aristarchus which proposed a Heliocentric or “sun centered” universe.  This theory was much simpler than that of Ptolemy – hence it satisfied Occam’s Razor – the philosophy that the simplest solution is usually the best one  Unfortunately this theory contradicted the doctrine of the Catholic Church  Copernicus published this work in Der Revolutionibus – The Revolution meaning the revolution of the planets about the sun. A book that was banned in 1616 by the Church

8. Alta High Astronomy Galileo Galilei Also a 16 th century astronomer, Galileo was an italian who first heard of the telescope (no he did not invent it!) and decided to construct one to look at the sky. In 1609 he used his telescope to observe  The moon Had craters and valleys  The phases of Venus Proved it went around the sun 4 moons of Jupiter  Callisto, Ganymede, Io, and Europa  The moons revolved around a planet other than earth

9. Alta High Astronomy The Trials of Galileo 1616 – his ideas were declared heretical by the Church 1633 – Placed under house arrest until his death 1992 – Formally Forgiven by the church

10. Alta High Astronomy Tycho Brahe Lived 1546 – 1601  Created the first formal observatory named Uraniborg on the Island of Hveen in Denmark  Most accurate “naked eye astronomer of his time  Spent more than 20 years charting the known heavens  Hired Johannes Kepler as an assistant to do his mathematical calculations

11. Alta High Astronomy Johannes Kepler German Mathematician – he was not a scientist. He had no theories about the universe he simply wanted a mathematical model to fit the data collected by Brahe. Hired by Brahe in 1600 he worked for 29 years on the three laws of planetary motion

12. Kepler’s laws of planetary motion Orbits are elliptical not circular A planet will sweep out equal areas in equal time. The time of orbit squared equals the distance to the sun squared ( p 2 = a 3 ) Alta High Astronomy

13. 1 st Law of Planetary Motion 1 st Law Planetary Orbits are elliptical, not circular  Two focal points – sun is at one foci, every point on the ellipse is the sum of the distances from the foci  Major Axis - length of the long part of the ellipse  Semi-Major Axis - Half the length of the major axis

14. Alta High Astronomy 2 nd Law of Planetary Motion 2 nd Law – a planet sweeps equal areas in equal times  This requires planets to speed up and slow down  Perihelion – When the planet is closest to the sun and moving fastest  Aphelion – When the planet is furthest from the sun and moving slowest

15. Alta High Astronomy 3 rd Law of Planetary Motion The period of a celestial bodies orbit squared is equivalent to the length of its semi-major axis cubed Mathematically: p 2 = a 3

16. Alta High Astronomy Sample problem If Earth is 1 AU from the sun and takes 365 days to go around the sun, how long does it take Mars to orbit the sun if it is 1.5 AUs from the sun?

17. Alta High Astronomy Solution Using the formula: p 2 = a 3 Rearrange it for each object

18. Alta High Astronomy Eccentricity Eccentricity – how far off you are from a perfect circle E = distance between foci/ length of the major axis Mathematically E = d/2a

19. Alta High Astronomy Newton Newton was an English Scientist He wanted to explain why Kepler’s Laws work Newton is famous for his three laws of motion which are the basis of Mechanics which is a branch of Physics

20. Alta High Astronomy Newton’s Laws of Motion An object at rest tends to stay at rest, and an object in motion tends to stay in motion. Acceleration is directly proportional to the force applied, and the mass is inversely proportional to it’s acceleration (F=ma) For every action there is an equal and opposite reaction

21. Alta High Astronomy Inertia: A resistance to change, a property of all matter.

22. Alta High Astronomy Newton’s Second Law The Law of Acceleration The acceleration of an object is in the direction of the force applied. Acceleration is directly proportional to the force applied. The harder you push an object the faster it goes Acceleration is inversely proportional to the mass of the object. The heavier the object, the less affect a push has.

23. Alta High Astronomy Newton’s Third Law Action - Reaction For every action there is an equal and opposite Reaction.

24. Alta High Astronomy Universal Gravitation Newton’s Law of Universal Gravitation states that any two objects with mass are attracted to each other The Force of Attraction is directly proportional to the product of the masses and inversely proportional to the square of the distance between them.

25. Alta High Astronomy Universal Gravitation F = Gm 1 m 2 /r 2 G – the universal Gravitation constant. Experimentally determined to be G = 6.67 x 10 -11 N m 2 /kg 2 M 1 & M 2 – the masses of the objects R 2 – the distance between the objects This law explains why an object speeds up when it is closer to the sun and slows down when it is further away