Lesson 1

• Astronomy 


  the study of everything in the universe beyond Earth's atmosphere
• Astronomy


  includes objects we can see with our naked eye and objects we can only see or with other instruments
• Sphere of the world

  by 5th century bc, earth was widely accepted to be a sphere
• In the 5th century B.C., Empedocles and Anaxagoras

  offered arguments for the spherical nature of the

  Earth.
• Earth is not a perfect sphere. Its shape is an oblate

  spheroid.
• Earth bulges at the equator because of the centrifugal

  force during rotation.
• Eratosthenes method was very simple; he measured

  the length of a shadow from a vertical stick of a

  known height in two cities on the same day.
• The Earth rotates on its axis relative to the sun every

  24.0 hours causing day or night.
• Orbit: Earth’s path as it revolves around the sun.
• Revolves in an oval shape called an ellipse.
• A revolution or orbit is the time it takes for the earth to

  make one complete revolution around the sun.
• The speed of earth’s revolution is 68,000 miles per

  hour.
• The earth's spin axis is tilted with respect to its orbital

  plane. This is what causes the seasons.
• When the earth's axis points towards the sun, it is

  summer for that hemisphere. When the earth's axis

  points away, winter can be expected.
• Perihelion

  Planet moves faster when it is nearer the Sun
• Aphelion 


  slower when it is farther from the Sun.
• Geocentric theory proposes that all objects including

  the moon, sun, stars orbit around the Earth.
• heliocentric theory proposes that all other

  objects including the Earth, moon, and stars move

  around the Sun.
• Geocentric Theory


  Idea come from Aristotle, explained by Ptolemy.
• Heliocentric Theory


  Copernicus - studied planetary movements and

  concluded that the sun was at the center and the

  planets/stars revolved around it.
• in geocentric theory, it is believed that God put the Earth at the center of the universe.
• part of heliocentric theory

  Johannes Kepler - planets move in elliptical orbits around the sun.