Ancient astronomy

• Astronomy - Study of universe beyond earth's atmosphere
• 500-430 B.C. - Anaxagoras further supported Pythagoras' proposal through his observations of the shadows that the Earth cast on

  the Moon during a lunar eclipse. He observed that during a lunar eclipse, the Earth's shadow was reflected on the Moon's surface. The shadow reflected was circular.
• • 500 B.C. - most Greeks believed that the Earth was round, not flat. It was Pythagoras and his pupils who were first to propose a spherical Earth.
• 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 - was 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.
• Aristotle - argued that if the Moon and the Sun were both spherical, then perhaps, the Earth was also spherical.
• Disappreaing ship - 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.
• 250,000 stadia = 40,000 kilometers
• Anaxagoras - was able to explain what causes the phases of the moon. According to him, the moon shone only by reflected sunlight. Since it is a sphere, only half of it illuminated at a time. This illuminated part that is visible from the earth changes periodically.

  
• 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. He learned that the sun was many time farther than the moon and that it was much larger than the earth. He also made an attempt to calculate the distance of the sun and the moon by using geometric principles.

  
• Eratosthenes - The first successful attempt to determine the size of the earth was made by him. He did this by applying geometric principles. He observed the angles of the noonday sun in two Egyptian cities that were almost opposite each other- Syene (now Aswan) in the south and Alexandria in the north. He assumed they were in the same longitude.

  
• 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. He developed a method for predicting the times of lunar eclipses to within a few hours. Aside from this, he also measured the length of the year to within minutes of the modern value.

  
• Claudius Ptolemy - He 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.

  
• phases of moon

  A) New moon

  B) waxing crescent

  C) first quarter

  D) waxing gibbous

  E) full moon

  F) waning gibbous

  G) last quarter

  H) waning crescent