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Ch. 22: Astronomers

Ch. 22: Astronomers. Mr. Litaker. Our Solar System . What do we know? . Time required for Earth to make one rotation on its axis?. 24 Hours. Revolution. Time required for Earth to make one revolution around the sun?. 365 ¼ Days. Time of Year. Winter.

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Ch. 22: Astronomers

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  1. Ch. 22: Astronomers Mr. Litaker

  2. Our Solar System • What do we know? Time required for Earth to make one rotation on its axis? 24 Hours

  3. Revolution • Time required for Earth to make one revolution around the sun? 365 ¼ Days

  4. Time of Year Winter • During what time of the year is the Earth closest to the sun? Perihelion The northern hemisphere tilted away from sun during winter resulting in less solar heating even though the earth is closer to sun. * During what time of the year is the Earth farthest from the sun? Summer Aphelion The northern hemisphere tilted towards sun resulting in more solar heating

  5. Orbit • What type of orbit does the Earth have around the sun? elliptical

  6. Early Astronomy Astronomy – is the science that studies the universe. Astronomy deals with the properties of objects in space and the laws under which the universe operates.

  7. Our Solar System The Historical Perspective • Aristotle • Ptolemy • Copernicus • Tycho Brahe • Kepler • Galileo • Newton

  8. Aristotle • Greek philosopher (384- 322 B.C.)  • Believed that the Earth was the center of the Universe. • Geocentric model – Earth Centered ** Thought – the Sun, Stars, and other Planets revolved around the Earth. • Concluded the Earth was round because… It always cast a curved shadow on the moon.

  9. Ptolemy 141 A.D. • Much of our knowledge of Greek astronomy comes from Claudius Ptolemy. • Supported Geocentric Model • Since Ptolemy’s model predicted motions of the planets, his model went unchallenged for nearly 13 centuries.

  10. Heliocentric Model Aristarchus– (312-230 B.C.) was the 1st to believe that the sun was the center of the universe. This was referred to as aHeliocentric model. Everything orbits the sun in this model.

  11. Viewpoints Even though Aristarchus provided some evidence of distances and sizes that were not completely accurate --- The Geocentric Model dominated western thought for nearly 2000 years!!!

  12. Nicolaus CopernicusCleric and Astronomer 1473 - 1543   Finally we shall place the Sun himself at the center of the Universe.All this is suggested by the systematic procession of events andthe harmony of the whole Universe, if only we face the facts,as they say, 'with both eyes open'.   

  13. Nicolas Copernicus “Copernican Revolution” The 1st Great Astronomer To emerge In the Middle Ages! • Polish astronomer (1473-1543) • Believed that the sun was the center of the solar system. • Heliocentric Model – Sun Centered

  14. Tycho Brahe • Tycho Brahe Danish Astronomer • (1546 – 1601) • Built an observatory financed by the king of Denmark.  • Made detailed observations and records of the planets. • Assisted by mathematician Johannes Kepler

  15. Johannes Kepler • German astronomer (1571- 1630) • Used the planet data of Tycho Brache and developed Kepler’s: Three Laws of Planetary Motion. • Look in the book and copy his 3 laws. • 618

  16. First Law • The First Law: • Planets move in ellipses with the Sun at one focus. Circular and Elliptical Orbits Having the Same Period and Focus

  17. 2nd Law • The radius vector describes equal areas in equal times. (The Second Law) • For a circle the motion is uniform as shown above, but in order for an object along an elliptical orbit to sweep out the area at a uniform rate, the object moves quickly when the radius vector is short and the object moves slowly when the radius vector is long.

  18. 3rd Law • The Third Law: • The squares of the periodic times are to each other as the cubes of the mean distances. • This law he published in 1619 in his Harmonices Mundi . It was this law, not an apple, that lead Newton to his law of gravitation. Kepler can truly be called the founder of celestial mechanics.

  19. Galileo Galilei

  20. Galileo Galilei • Italian Mathematician (1564 – 1642) • Invented the telescope in 1608 and observed… ? Look in the book on page 619 and list the 5 discoveries Galileo made with his telescope.

  21. Galileo • Galileo quickly discovered that our Moon had craters, that Jupiter had it's own moons, that the Sun has spots, and that Venus has phases like our Moon. Galileo, who lived from 1564 to 1642, made many more discoveries. Galileo claimed that his observations only made sense if all the planets revolved around the Sun, as championed by Aristarchus and Copernicus, not the Earth, as was commonly believed then. The powerful Inquisition made Galileo publicly recant this conclusion, but today we know he was correct.

  22. Newton

  23. Isaac Newton • English Scientist 1643 to 1727 • Recognized as the greatest Scientific intellect of all time. • Best known for his laws of motion and universal gravitation formula. • What does the Law of Universal Gravitation state ?

  24. Play CD: Discover Astronomy Section II

  25. Earth – Moon Relationships

  26. Sidereal Day vs. Solar Day • Solar Day – 24 Rotation using the Sun as our reference. • Sidereal Day – 23 hours 56 minutes for one complete rotation using a star other than the sun. There is a loss of 4 minutes or 10. Power Line Example: At Night

  28. What season is the Northern Hemisphere experiencing? Where is the most direct rays striking? Summer Tropic of Cancer

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