Science W1

• ERATHOSTHENES proved that the Earth is round based on the shadows that was different in one area to another (Egypt vs Greece)
• Greeks deduced that Earth is spherical based on the shadow cast during Lunar Eclipse
• Diurnal motion


  Daily motion of celestial bodies in the sky
• Diurnal motion


  • Caused by Earth's rotation on its axis
• Annual motion


  Yearly motion of celestial bodies across the sky
• Annual motion

  • Caused by Earth's revolution around the sun
• Zodiac


  • 13 constellations seen in the ecliptic
• Equinox


  2 days in a year in which the sun crosses the Earth's plane of celestial equator (equal day & night)
• Solstice


  • 2 days in which the sun is farthest from the Earth's plane of celestial equator
  • Summer solstice - longest day
  • Winter solstice - shortest day
• Solar eclipse


  Moon passes between Earth and Sun, blocking the view of the Sun
• Lunar eclipse


  Earth directly aligns between sun and moon, earth casts a shadow on the moon
• Geocentric model


  Earth is the center of the universe, celestial bodies revolve around the Earth
• Heliocentric model


  Sun is the center of the universe, all planets including Earth revolve around the sun, moon revolves around Earth
• Tycho Brahe: moon and sun revolve around earth, all other planets revolve around the sun
• Kepler's 1st Law (Law of Ellipse)

  • Orbits of planets are elliptical with the sun at one of the foci
• Kepler's 2nd Law (Law of Equal Areas)


  • A line joining a planet and the sun sweeps out equal areas in space in equal intervals of time (planets move fastest when nearest the sun)
• Kepler's 3rd Law (Law of Harmony)


  • The square of a planet's orbital period (years) is proportional to the cube of the semi-major axis of its orbit (AU)