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• Many people observed that the moon and the sun rose in the east and set in the west
• Earth's movement


  1. Moves around its axis (rotation)

  2. Moves around the sun (revolution)
• Rotation


  Earth's movement around its axis
• A complete rotation takes 23 hours and 56 minutes
• Day-night cycle


  Created by Earth's rotation
• Earth's rotation

  Affects the temperature on Earth within a day
• Day


  Experienced in the part of the Earth where the sun shines
• Night


  Experienced on the unlit part of the Earth
• Revolution


  Earth's movement around the sun
• It takes 365.25 days for Earth to revolve around the sun
• Every four years, an additional day is added to the calendar to compensate for the extra hours (leap year)
• Perihelion


  Earth is closest to the sun
• Aphelion


  Earth is farthest from the sun
• Earth's axis is tilted 23.5 degrees
• Earth's tilt


  Causes the North Pole and the South Pole to lean toward or away from the sun at different times of the year
• Winter in the Northern Hemisphere

  When the North Pole is farthest or turned away from the sun, the area receives only indirect sunlight and gets cold
• Summer in the Northern Hemisphere

  When the North Pole is leaning towards the sun, the region receives direct sunlight
• Seasons


  Bring different amounts of sunlight, affecting the length of the day
• Days are shortest in the winter and longest in the summer
• Distance from the equator

  Greater effect of the amount of sunlight on the length of the day
• Angle of sun's rays


  When they strike at a 90 degrees angle, energy and temperatures in these areas are at the highest
• At the equator, the sun's rays hit an angle between 23 degrees North and 23 degrees South latitude, the heat is intense
• Angle of sun's rays


  The closer you are to the pole, the less intense the radiation and the colder the climate gets
• Celestial Equator


  Imaginary circle created by projecting Earth's equator into space
• Solstices


  Days when the sun is farthest from the northern and southern points above the celestial equator
• Summer Solstice

  Marks the beginning of summer, usually falls on June 21 or 22, the longest day of the year
• Winter Solstice


  Marks the beginning of winter, usually falls on December 21 or 22, the shortest day of the year
• Ecliptic


  Path of the apparent motion of the sun in the sky throughout the year as observed from Earth
• Equinoxes


  Occur when the ecliptic intersects the celestial equator, days on which night and day have equal duration
• Vernal Equinox


  Occurs in March, marks the beginning of spring in the Northern Hemisphere and of autumn in Southern Hemisphere
• Autumnal Equinox


  Occurs on late September, marks the beginning of autumn in the Northern Hemisphere and spring in the Southern Hemisphere
• Solar altitude


  Varies during solstices and equinoxes because of the change in the relative orbital position of Earth with respect to the sun
• Solar Altitude


  Apparent height of the sun in the sky, measured from either the northern or southern point along the horizon, maximum is 90 degrees when the sun is directly overhead