module 2

• Astronomy


  The science of the universe outside of our planet
• For thousands of years, humans have looked at the night sky and wondered about the stars
• With only the unaided eye, they neither saw nor dreamed that the stars are greater in number than all the grains of sand on all the beaches of the world
• Nor did they realize that the sun is a star – simply the nearest star to us in the universe
• Moon


  Perceived as a flat circular disk rather than as a three-dimensional sphere
• The roots of astronomy reach back to prehistoric times when humans first noted stars in the night sky
• What early astronomers did

  • Divided the night sky into groups of stars called constellations
  • Assigned names to the constellations, mainly from Greek, Babylonian and Egyptian astronomers
  • Grouping of stars and significance given to them varied from culture to culture
  • Constellations stimulated story-telling and creation of great myths
  • Constellations honored great heroes or served as navigational aids
  • Constellations provided a guide for planting and harvesting crops
• Charts of the periodic movements of constellations became some of the earliest astronomical records
• Even before the advent of the telescopes, ancient astronomers were able to observe the rising and setting of the Sun in the east and the west, respectively, the point where the Sun rises and sets in the horizon varies in a year, phases of the moon, lunar eclipse, solar eclipse, daily and annual motion of the stars, and planets Mercury, Venus, Mars, Jupiter, and Saturn
• Gnomon


  A primitive version of a sundial used by Babylonian and Egyptian civilizations to systematically observe the motion of the Sun
• Babylonian and Egyptian civilizations observed that the points where the Sun rises and sets on the horizon varies over a year and these variations happen periodically, and they concluded that seasonal changes in climate happen during a course of one year
• The stars continue to circle during the day, but the brilliance of the Sun makes them difficult to see
• Earth's orbit and axis

  • Earth's orbit around the Sun is slightly elliptical, not a perfect circle
  • Earth's axis is tilted approximately 23.4° to the plane of its orbit, not perpendicular
• Ecliptic


  The path the Sun appears to take around the celestial sphere each year
• Moon


  A relatively small object that is orbiting around a planet
• Earth's moon is the fifth biggest moon in the solar system, and the distance between the Earth and the moon is 384,000 kilometres on average
• Sidereal month


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


  The time it takes for the Moon to complete one cycle of phases, which is about 29.5 days
• Lunar phases


  • New moon
  • First quarter
  • Full moon
  • Third or last quarter
• The full moon nearest the autumnal equinox, which occurs about September 23, is called the harvest moon, and the full moon of the following month is known as the hunter's moon
• Moon phases


  • First quarter
  • Waxing crescent
  • Waxing gibbous
  • Full moon
  • New moon
  • Waning crescent
  • Last quarter
  • Waning gibbous
• Harvest moon


  The full moon nearest the autumnal equinox, which occurs about September 23 (when the days and nights are of equal length), rises with the least delay of all and lights the way for late-working harvesters
• Hunter's moon


  The full moon of the following month after the harvest moon, also an early riser
• Third or last quarter moon

  Seen illuminated on half the side facing the earth, rises about midnight, is highest at dawn and sets about noon, in the western sky in the morning, rides high in the havens in fall and low in spring and follows a middle course in summer and winter
• Waning crescent moon


  The following crescent gets thinner and thinner as it approaches the phase of the new moon to complete the cycle
• Earthshine


  Sunlight reflected to the moon from the daylight region of the earth, making the rest of the disc dimly illuminated within the horns of the bright waxing or waning crescent
• Gibbous moon


  The moon appears as a lopsided globe between the full and the two quarter phases
• Waxing and waning of the moon

  1. During the next seven days, progressively more and more of the moon's exposed view becomes illuminated (waxing crescent phase)

  2. The cycle reverses during the following two weeks as we see less and less of the sunlit side while the moon continuously moves in its orbit (waning gibbous)
• Lunar eclipse


  Occurs when the moon passes into the shadow of the earth, usually precedes or follows a solar eclipse by two weeks, may be partial or total
• Solar eclipse


  Occurs when the moon's shadow falls on the earth, causes darkness during the day (totality) which lasts 2-3 minutes on average, up to a maximum of 7.5 minutes
• Differences between lunar and solar eclipses

  • Lunar eclipse: Moon passes through Earth's shadow
  • Solar eclipse: Sun's light is blocked by the Moon
  • Lunar eclipse happens during a full moon
  • Solar eclipse happens during a new moon
  • Lunar eclipse occurs about twice every one year
  • Solar eclipse occurs about twice every three years
  • Lunar eclipse lasts for about an hour
  • Solar eclipse lasts 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, causing the apparent east to west movement of stars and other celestial bodies
• Annual motion


  The apparent yearly movement of the stars as observed from Earth as a direct effect of the Earth's revolution around the sun, causing changes in the sun's altitude and sunrise/sunset points throughout the year
• Precession of the equinoxes

  The apparent motion of the equinoxes along the ecliptic as Earth 'wobbles', happening about every 26,000 years, causing the North Pole to eventually point to a different star (Vega)
• Planets discovered before the invention of the telescope

  • Mercury
  • Venus
  • Mars
  • Jupiter
  • Saturn
• Mercury


  • Smallest and fastest planet, very close to the sun, has extreme temperatures, hard to observe directly except during transits across the sun
• Venus


  • Second planet from the sun, very bright, rotates clockwise (backwards), has a scorching greenhouse-like environment
• Mars


  • The "reddish" planet, has seasons, varied landscape, polar ice caps, dust storms, two small moons
• Jupiter


  • A huge planet shrouded in thick clouds, cannot see its surface
• Martian tectonism


  • Differs from Earth's tectonics, involves vertical movement with hot lava pushing upwards through the crust to the surface