PSCI - Chapter 6

• The Ancient Greeks considered Earth to be enclosed in a hollow sphere called the celestial sphere, where the stars, the sun, and other heavenly bodies are embedded.
• The points where Earth's rotational axis cuts this sphere are called the north celestial pole (NCP) and the south celestial pole (SCP).
• Celestial equator - the projection of Earth's equator in the celestial sphere.
• ecliptic - the path that the sun appears to take around the celestial sphere. It is inclined 23.5 degrees with respect to the celestial equator.
• solstices - two points on the ecliptic with the greatest distance from the celestial equator.
• The point where the sun is at its northernmost position above the celestial equator of at its highest in the sky is called the summer solstice. It is sometimes called the June solstice because it happens on or near June 21. Day is longest and night is shortest during the summer solstice.
• The winter or December solstice occurs when the sun is at its southernmost position or at its lowest in the sky. This normally happens on or near December 21. Day is shortest while night is longest during the winter solstice.
• equinoxes - the two points where the ecliptic intersects the celestial equator.
• The autumnal equinox happens on or near September 22. The vernal or spring equinox happens on or near March 21.
• constellations - the ecliptic traces through a series of star clusters. This sequence of constellations is called the zodiac.
• Earth requires 26, 000 years to complete one cycle of precession.
• Earth's precession was historically called precession of the equinoxes because the position of the equinoxes was slowly and gradually changing with respect to some background stars.
• Hipparchus of Nicaea (known today as Turkey) - was credited for having discovered the precession of the equinoxes. He is said to have made a catalog of stars in the sky, noting their exact positions in latitudes and longitudes. He compared their positions with those measured by Timocharis about 150 years earlier.
• precession - change in the orientation of the rational axis of any rotating body.
• there are 12 principal constellations of the zodiac
• It takes 24 hours for Earth to rotate about its axis from west to east.
• diurnal motion - the apparent daily motion of stars and other celestial bodies across the sky caused by Earth's rotation about its axis.
• lunisolar precession - earth's precession due to the gravitational pull of the moon and the sun.
• annual motion - the apparent motion of the sun caused by the earth's revolution around it.
• 365.24 days - for earth to make one complete revolution around the sun
• leap years - years where an extra, or intercalary, day is added to the end of the shortest month, February.
• the early humans relied on the skies as their principal means of telling the time, of navigation and knowing when to start planting crops.
• khufu, khafre, menkaure - the pyramids of Giza were royal tombs built for three different pharaohs.
• Scientists estimate it took at least 20,000 workers over 23 years to build the Great Pyramid of Giza.
• In the 17th century, archaeologist John Aubrey made the claim that Stonehenge was the work of the Celtic high priests know as the Druids.
• all four sides of the pyramid (palenque) have approximately 91 steps which, when added together and including the temple platform on top as the final "step", may produce a total of 365 steps.
• geocentric universe - "geo" means "earth" considers earth as the center of the universe
• heliocentric universe - "helio" means "sun" assumes the sun to be the center of the universe
• astronomer - space scientist whose main job is to conduct research about outer space and the universe through earth-based observatories.
• astronaut - a professional space traveler trained to do specific missions outer space.
• Neil Armstrong - first man to walk on the surface of the moon. He stepped on the moon on July 20, 1969 at 10:56 eastern daylight time.
• Neil Armstrong was on the Apollo 11 on the way to moon together with Buzz Aldrin and Michael Collins.
• Buzz Aldrin stepped on the moon 19 minutes later after Neil Armstrong stepped on the surface of it. Michael Collins did not step on it since he was the "Pilot" of their aircraft.
• Thales of Miletus - in 600 BCE, he proposed that the Earth is a disk of floating on water.
• Anaximander - in 520 BCE, suggested that Earth is a cylinder and that it's surface is curved.