PhySci

• Oblate spheroid


  The shape of the Earth. It has bulging equator and squeezed poles.
• Solstice


  Either of the two times in the year, the summer solstice and the winter solstice, when the sun reaches its highest or lowest point in the sky at noon, marked by the longest and shortest days
• Eclipse


  An obscuring of the light from one celestial body by the passage of another between it and the observer or between it and its source of illumination.
• Heliocentrism


  The astronomical model in which the Earth and planets revolve around the Sun.
• Geocentrism


  Any theory of the structure of the solar system (or the universe) in which Earth is assumed to be at the center of it all.
• Around 500 B.C., most Greeks believed that the Earth was round, not flat.
• Pythagoras and his pupils were first to propose a spherical Earth.
• Anaxagoras further supported Pythagoras' proposal through his observations of the shadows that the Earth cast on the Moon during a lunar eclipse.
• Around 340 B.C., Aristotle listed several arguments for a spherical Earth which included the positions of the North Star, the shape of the Moon and the Sun, and the disappearance of the ships when they sail over the horizon.
• North Star


  Believed to be at a fixed position in the sky. However, when the Greeks traveled to places nearer the equator, like Egypt, they noticed that the North Star is closer to the horizon.
• Shape of the Moon and Sun

  Aristotle argued that if the Moon and the Sun were both spherical, then perhaps, the Earth was also spherical.
• Disappearing ships


  If the Earth was flat, then a ship traveling away from an observer should become smaller and smaller until it disappeared. However, the Greeks observed that the ship became smaller and then its hull disappeared first before the sail as if it was being enveloped by the water until it completely disappeared.
• Anaxagoras was able to explain what causes the phases of the moon.
• Eudoxus proposed a system of fixed spheres. He believed that the Sun, the moon, the five known planets and the stars were attached to these spheres which carried the heavenly bodies while they revolved around the stationary Earth.
• Aristotle was a student of Plato. For him, the earth is spherical in shape since it always casts a curved shadow when it eclipses the moon. He also believed that the earth was the center of the universe. The planets and stars were concentric, crystalline spheres centered on the earth.
• Aristarchus is the very first Greek to profess the heliocentric view. The word helios means sun; centric means centered. This heliocentric view considered the sun as the center of the universe.
• Aristarchus made an attempt to calculate the distance of the sun and the moon by using geometric principles. He based his calculations on his estimated diameters of the earth and moon, and expressed distance in terms of diameter. However, the measurements he got were very small and there were a lot of observational errors.
• The first successful attempt to determine the size of the earth was made by Eratosthenes. He did this by applying geometric principles.
• Hipparchus is considered as the greatest of the early Greek astronomers. He observed and compared the brightness of 850 stars and arranged them into order of brightness or magnitude.
• Claudius Ptolemy believed that the earth was the center of the universe. His Ptolemic Model claimed that the planets moved in a complicated system of circles. This geocentric model also became known as the Ptolemic System.
• According to the Ptolemic Model, the sun, the moon, and the other planets move in circular orbits around the earth. However, if observed night after night, these planets move slightly eastward among the stars.
• Retrograde motion


  The westward drift of the planets
• Aristotle considered the position of the North Star. The farther north you journeyed, the closer the North Star seemed to move to the middle of the sky. But if someone were to travel south of what we now call the equator, the North Star could not be seen at all.
• Aristotle observed that at a distance, he could see the tops of ships' sails before he saw the rest of the ship. He deduced that this was because of the curvature of the earth.
• Astronomy is the science of the universe outside of our planet. This is the branch of physical science dealing with heavenly bodies.
• Astronomy has resulted in many practical inventions, ideas, including calendars, navigational techniques, laws of motion, engineering of products and an increased understanding of energy and weather.
• Moon


  A natural object that orbits a larger object.
• Eclipse


  When one celestial body such as a moon or planet moves into the shadow of another celestial body.
• 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. It refers to the apparent movement of stars and other celestial bodies around Earth.
• Circumpolar stars


  Stars that never seem to go away from the horizon, or never set or rise.
• 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.
• Ecliptic


  The path on the celestial sphere that the sun revolves around.
• Equinoxes


  The two points during the year when the sun intersects the celestial equator and the length of daytime is almost equal to the length of nighttime.
• Precession of the equinoxes

  The apparent motion of the equinoxes along the ecliptic as Earth 'wobbles,' and this motion happens about every 26 000 years.
• Planets Discovered Before the Invention of Telescope

  • Mercury
  • Venus
  • Earth
  • Mars
  • Jupiter
  • Saturn
• Planets Discovered Before the Invention of Telescope (continued)

  • Uranus
  • Neptune
• The size and distance of the planets are not drawn to scale.
• Using the data provided, create a scaled model of the distances of the planets in the solar system. Indicate the scale used. The distances should be proportional to the actual size.