physci

• Spherical Earth


  Proposed by Pythagoras and his pupils around 500 B.C.
• Anaxagoras


  • Supported Pythagoras' proposal by observing the shadows that the Earth cast on the moon during a lunar eclipse (500 to 430 B.C.)
• Aristotle


  • Listed several arguments for a spherical Earth around 340 B.C. (position of the North Star, shape of the Moon and the Sun, observation from ship traveling away)
• Eratosthenes


  Greek scientific writer, astronomer, and poet who made the first measurement of the size of Earth for which any details are known (born c. 276 BCE, died c. 194 BCE)
• Eratosthenes' method


  1. Measured the angle the Sun made with the vertical direction in Alexandria and Syene

  2. Hypothesized that the light rays coming from the Sun were parallel and the Earth was curved

  3. Computed the circumference of the Earth to be approximately 250,000 stadia (about 40,000 km)
• Astronomical Phenomena


  Events observable in the sky as studied by the scientific discipline of astronomy
• Celestial Sphere


  An imaginary sphere where all objects in heavens are projected, useful in pinpointing objects in space as well as defining Earth-based positions relative to the sky
• Diurnal Motion


  The apparent daily motion of celestial objects from east to west in which celestial objects seem to rise and set
• Annual Motion


  The apparent yearly movement of the Earth across a background of stars, caused by Earth's revolution around the Sun
• Phases of the Moon or Lunar Phases


  • New Moon
  • Waxing Crescent
  • First Quarter
  • Waxing Gibbous
  • Full Moon
  • Waning Gibbous
  • Third Quarter
  • Waning Crescent
• New Moon


  The side of the moon that is facing Earth is not illuminated by the sun
• Waxing Crescent


  The moon appears as a thin crescent shape in the sky, with only a small portion of its surface illuminated
• First Quarter


  The moon appears as a half-circle in the sky, with exactly half of its surface illuminated by the sun
• Waxing Gibbous


  The moon appears in a mostly illuminated crescent shape, with only a small part appearing dark
• Full Moon


  The entire face of the Moon that is visible from Earth is fully illuminated
• Waning Gibbous


  The Moon appears as a large and bright, but gradually shrinking, crescent shape in the sky
• Third Quarter


  The Moon appears as a half-moon shape, with half of its face illuminated by sunlight
• Waning Crescent


  The Moon appears as a thin crescent, with a small portion of its face illuminated by sunlight
• Eclipse


  The total or partial obscuring or another of one celestial body by another
• Solar Eclipse


  The Moon passes between the Sun and Earth, casting the Moon's shadow on Earth that either fully or partially blocks the Sun's light in some areas
• Lunar Eclipse


  The earth's shadow blocks out our view of the moon during the full moon
• Geocentrism


  The idea that the Earth is the center of the universe, popularized by Ptolemy in 150 BCE
• Heliocentrism


  The idea that the sun, not the Earth, is the center of the universe, argued by Copernicus in 1543
• Tycho Brahe


  • Developed an early interest in astronomy, made significant astronomical observations, designed and built new instruments, calibrated them, and instituted nightly observations (1546-1601)
• Tycho Brahe's model


  • The Earth is at the center of the universe, the Sun and Moon and the stars revolve around the Earth, and the other five planets revolve around the Sun
• Johannes Kepler


  • Became Tycho Brahe's successor, was given access to Brahe's data on Mars, and formulated his three laws of planetary motion (1571-1630)
• Kepler's Three Laws of Planetary Motion


  • Law of Ellipses: The path of the planets about the Sun is elliptical in shape, with the center of the Sun being located at one of the foci
  • Law of Equal Areas: An imaginary line drawn from the center of the Sun to the center of the planet will sweep out equal areas in equal intervals of time
  • Law of Harmonies: The square of the period of a planet orbiting around the sun and the cube of the long radius are proportional to each other