Mod.2

• Celestial bodies observed


  • The Sun
  • Phases of the moon
  • Lunar eclipse
  • Solar eclipse
  • Daily and annual motion of the stars
  • Planets Mercury, Venus, Mars, Jupiter, and Saturn
• Rising and setting of the Sun


  1. Observed by Babylonian and Egyptian civilizations using a gnomon

  2. Sun rises in the eastern part of the sky, reaches its highest point in midday, and sets in the western part of the sky

  3. Variations in the points where the sun rises and sets on the horizon over a year, related to weather and seasonal changes
• Stars continue to circle during the day, but the brilliance of the Sun makes them difficult to see
• The Moon can often be seen in the daylight
• If Earth orbited the Sun in a perfect circle and Earth's axis was perpendicular to the plane of its orbit


  The Sun would rise and set at the same times every day and take the same path across the sky every day of the year
• Earth's orbit around the Sun is slightly elliptical
• Earth's axis is tilted approximately 23.4° to the plane of its orbit
• When the North Pole is tilted toward the Sun


  The Northern Hemisphere experiences summer, and the Sun is high in the sky at noon
• When the North Pole is tilted away from the Sun


  The Northern Hemisphere experiences winter, and at noon the Sun doesn't get nearly as high in the sky
• The longest day of the year occurs on the summer solstice (usually around June 21)
• The shortest day of the year occurs on the winter solstice (usually around December 21)
• The Sun's position in our sky changes day to day due to Earth's elliptical orbit and tilt of its axis
• Ecliptic


  The path the Sun appears to take around the celestial sphere each year
• The Sun rises about 4 minutes later each day with respect to the stars
• Moon


  A relatively small object that is orbiting around a planet
• Earth's moon is the fifth biggest moon in the solar system
• The distance between the Earth and the moon is 384,000 kilometres on average
• The moon is about four times smaller than the width of the Earth
• One face of the moon is always facing us, and we can never see the other side
• Half of the moon is always lit by sunlight and the other half is in shadow
• Sidereal month


  The time it takes for the moon to complete one full orbit around Earth, 27 days, 7 hours, and 43 minutes
• Synodic month


  The time it takes for the moon to complete one cycle of phases (from full Moon to full Moon), about 29.5 days
• Phases of the moon


  • New moon
  • Waxing crescent
  • First quarter
  • Waxing gibbous
  • Full moon
  • Waning gibbous
  • Last quarter
  • Waning crescent
• At any given moment rays of sunlight illuminate one-half of the moon's surface
• The new moon phase occurs when the sun, moon and earth are lined up, with the moon in the middle
• The full moon rises in the east as the sun sets in the west, and stays up all night long
• The full moon nearest the autumnal equinox is called the harvest moon, and the following month's full moon is called the hunter's moon
• Earthshine is sunlight reflected to the moon from the daylight region of the earth
• Between the full and the two quarter phases, the moon appears as a lopsided globe, called the gibbous moon
• Types of eclipses


  • Lunar eclipse
  • Solar eclipse
• Lunar eclipse


  Moon passes through the Earth's shadow
• Solar eclipse


  Sun's light is blocked by the Moon
• Lunar eclipses happen during a full moon, while solar eclipses happen during a new moon
• Lunar eclipses occur about twice every one year, while solar eclipses occur about twice every three years
• Lunar eclipses last for about an hour, while solar eclipses last for a few minutes
• Diurnal motion


  The apparent daily revolution of the celestial sphere around the celestial poles as a direct effect of the Earth's rotation on its axis
• The apparent motion of celestial bodies viewed from Earth is east to west
• The apparent daily motion of the sun is counter-clockwise, with the sun rising in the east and setting in the west
• Diurnal motion


  • Apparent daily revolution of the celestial sphere around the celestial poles as a direct effect of the Earth's rotation on its axis
  • Apparent movement of stars and other celestial bodies around Earth
  • Circular path that the celestial bodies take to complete the diurnal motion is called diurnal circle
  • Apparent motion of celestial bodies viewed from Earth is east to west
  • Stars seem to move in a counter-clockwise direction (from east to west) with respect to Polaris or North Star
  • Apparent daily motion of the sun is counter-clockwise
  • Sun rises in the east and sets in the west
  • Stars called circumpolar stars never seem to go away from the horizon, or never set or rise
  • Closer you get to the poles, the larger the circle of circumpolar stars is
  • Nearer you get to the equator, the circle of circumpolar stars decreases until it vanishes at the celestial poles
• Annual motion


  • Apparent yearly movement of the stars as observed from Earth as a direct effect of the Earth's revolution around the sun
  • Sun revolves 360 degrees a year around a path on the celestial sphere called the ecliptic
  • Sun moves eastward with respect to the stars on the celestial sphere
  • Sun's altitude changes with season, maximum during summer solstice and minimum during winter solstice
  • Sunrise and sunset points in the horizon changes with season, north of east in summer and south of east in winter
  • Different stars and constellations appear on the horizon throughout the year, known as the constellations of the Zodiac