PHYSICAL SCIENCE

• Astronomy


  A branch of natural science that deals with the study of celestial objects and phenomena that occur in the cosmos
• Astronomy


  • Uses mathematics, physics, and chemistry to try and explain the origin and evolution of celestial objects
• Objects of interest in astronomy

  • Planets
  • Moons
  • Stars
  • Nebulae
  • Galaxies
  • Comets
• Ancient Greeks


  Major contributors to different fields of knowledge including philosophy, mathematics, and science
• How ancient Greeks deduced the Earth is spherical

  1. Observed the circular shadow cast by the Earth during lunar eclipses

  2. Measured the diameter and circumference of the Earth using geometry
• Evidence for the Earth being spherical

  • Position of the North Star
  • Shape of the moon and sun
  • Disappearance of ships over the horizon
• How Eratosthenes measured the Earth's circumference


  1. Used a stick, knowledge of the distance from Alexandria to Syene, and geometry

  2. Measured the angle the sun made with the vertical direction by measuring the shadow cast by a vertical stick

  3. Computed the circumference to be approximately 250,000 stadia (40,000 km)
• Anaxagoras


  Explained the causes of the moon's phases, proposed the moon shone only by reflected sunlight
• Aristarchus


  Proposed the sun was the center of the universe
• Hipparchus


  Compiled a catalogue of 850 stars, developed a method for predicting lunar eclipses
• Ptolemy


  Proposed the geocentric model of the universe with the Earth at the center
• Eudoxus' model


  • Composed of 27 concentric spheres with the Earth at the center
• Aristotle's model


  • Considered Eudoxus' spheres as physical entities filled with divine and eternal ether, introduced the Prime Mover as the cause of movement
• Aristarchus' model


  • The sun is the center of the universe, the moon orbits the spherical Earth which orbits the sun, the stars are very far away
• Hipparchus' model


  • Hipparchus is the Father of Trigonometry
• Ptolemy's model


  • The Earth is the center of the universe, all planets including the moon revolve around it
• Copernicus' model


  • The sun is the center of the universe, not the Earth
• Brahe's model


  • Combination of Ptolemaic and Copernican models, planets revolve around the sun but the Earth is the center of the universe
• How Babylonians and Egyptians observed the motion of the sun


  Used a sundial (gnomon) to systematically observe the sun's motion through its shadow
• Observation made: Sun rises in the East and sets in the West
• Astronomical phenomena observed before the telescope: Rising and setting of the sun, formation of seasons, phases of the moon, eclipses, daily and annual motion of stars
• Solar eclipse


  Occurs when the moon passes between the Earth and the Sun, with the moon casting a shadow on the Earth's surface
• Lunar eclipse


  Occurs when the Earth is directly aligned between the Sun and the Moon, with the Earth casting a shadow on the moon
• Diurnal motion


  The apparent daily motion of stars and other celestial bodies across the sky due to the Earth's rotation
• Annual motion


  The apparent yearly motion of stars and other celestial bodies across the sky due to the Earth's revolution
• Zodiac and the Ecliptic


  • A band of thirteen constellations collectively called the zodiac can be seen in the ecliptic, which change through the months
• Equinoxes and Solstices


  • Equinoxes are the two days in a year when the sun crosses the celestial equator, solstices are the two days when the sun is at the farthest declination from the celestial equator
• Precession of the Equinoxes


  The slow "wobbling" of the Earth's axis of rotation due to the gravitational pull of the moon and sun, spanning a period of 25,920 years
• Planets discovered before the telescope

  • Mercury
  • Venus
  • Mars
  • Jupiter
  • Saturn
• Tycho Brahe


  Danish astronomer who continuously and precisely recorded the positions of the sun, moon, and planets for over 20 years using giant-like protractors, made accurate observations of celestial body movements, proposed the geo-heliocentric model
• Johannes Kepler


  German astronomer, mathematician, and astrologer who was Brahe's assistant, formulated the Laws of Planetary Motion
• Kepler's 1st Law (Law of Ellipse)


  • Orbits of all planets are elliptical with the Sun at one focus of the ellipse
• 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, so a planet moves fastest when nearest to 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 semimajor axis of its orbit (in astronomical units or AU), so larger orbits take longer to complete