Physical science

• Boiling point is the temperature at which a liquid substance changes into a gas state.
• Celestial Sphere: Ancient Greek considered Earth to be enclosed in a hollow sphere where the stars, the sun and other heavenly bodies are embedded.
• NCP or North Celestial Pole and SCP or South Celestial Pole: points where Earth’s rotational axis cuts this sphere are called.
• Ecliptic: Path that the sun appears around the celestial sphere, inclined 23.5 degrees with respect to celestial equator.
• Solstice: points on the ecliptic where with the greatest distance from the celestial equator.
• Although Tycho Brahe was precise in his measurement, he believed in Geocentric Model.
• Johannes Kepler, a believer of Heliocentric Model, analyzed the motion of the planets and developed three fundamental laws of planetary motion.
• Tycho Brahe made the correct model of the solar system with his careful, accurate measurements of the stars and planets over 20 years.
• Galileo Galilei used his first telescope in 1609 to study the moon, the stars and the sun; he supported the Heliocentric Theory.
• Summer Solstice: point where the sun is at the northernmost position above the celestial equator or at its highest in the sky; day is at its longest and night is at shortest; usually happens June 21.
• Winter Solstice: point where the sun is at the southernmost position above the celestial equator or at its lowest in the sky; night is at its longest and day is at shortest; usually happens December 21.
• Equinoxes: two points where ecliptic intersects the celestial equator, at this point, Earth rotational axis is perpendicular to the line joining the Earth and the Sun; day and night are equal in duration; Autumnal equinox happens September 22, while Vernal or Spring Equinox happens March 21.
• North Star: The North Star was believed to be at a fixed position in the sky, however, when the Greeks travelled to places nearer the equator, like Egypt, they noticed that the North Star is closer to the horizon.
• Shape of the Sun and the Moon: 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.
• The Size of the Spherical Earth: It was Eratosthenes who gave the most accurate size during their time, while he was working at the Library of Alexandria in Northern Egypt, he received correspondence from Syene in Southern Egypt which stated that a vertical object did not cast any shadow at noontime during the summer solstice, but this was not the case in Alexandria where, at noon time during the summer solstice, a vertical object still casts a shadow.
• The Shape of the Earth: The strongest evidence of the Earth’s shape is by looking at the moon during Lunar Eclipse, the earth’s shadow was always a circle and the only shape in three dimension that casts a circular shadow is a sphere.
• Plato’s Principle of Saving Appearances states that the true motion of the heavenly bodies are not visible to the naked eye but only exist in the mind.
• Claudius Ptolemy’s Epicycles were able to describe the retrograde motions of the planet as well as the different distances of the planets from the Earth at different times.
• The outer sphere in Plato’s model is composed of fixed stars rotating around the earth once every 23 hours 56 minutes, and a solar sphere that rotated once every 24 hours and contained the sun.
• Beyond the crystalline sphere containing the stars was an infinite void in Plato’s model.
• Celestial Motion refers to the motion of the Earth and other celestial bodies.
• As civilization flourished, several other models were proposed.
• Hipparchus of Nicaea (Turkey) was credited for having discovered precession of Equinoxes.
• Anaximander suggested that the Earth is a cylinder and that its surface is a curved.
• Nicolaus Copernicus developed his own celestial model of a heliocentric planetary system.
• Aristotle believed that the Earth was the center of the universe.
• Eudoxus believed that the planet and the stars revolve around the earth in non uniform circular motion but retrogade motion which means that the planets over time appears to slow down, stop and change direction and move backward.
• Copernicus explained why outer planets like Mars, Jupiter, and Saturn were brightest in opposition.
• Around 600 BCE, Thales of Miletus proposed that the Earth is a disk on a floating water.
• Aristotle’s model of the universe includes spheres to describe the planetary motion.
• Diurnal Motion is the daily rotation of the Earth and the moon, and the stars and the Sun.
• Precession of the Equinoxes is the change in the orientation of the rotational axis of any rotating body.
• Plato’s Model of Universe is made up of two crystalline spheres.
• Heliocentric Model assumes the sun to be the center of the universe.
• Annual Motion is the Earth’s absolute motion on its orbit around the Sun.
• Aristarchus was the first to introduce the sun centered solar system.
• Geocentric Model considers the Earth as the center of the universe.
• The True shape of the Earth is not a perfect sphere rather it is characterized as Oblate Spheroid.
• Greeks’ Perspective of Earth’s Motion: Aristotle identified two general type of motions, Celestial Motion - motion of the planets, the Moons, and the stars, Terrestrial Motion - motion of everyday objects, Natural Motion - all things in the terrestrial realm were made out of the four elements – air, earth, fire, and water.