ANCIENT ASTRONOMY

• Greeks: They are much noted for their contributions in different fields. They were not only great philosophers but great scientists and mathematicians as well.
• Ptolemic Method


  It claims that the planets moved in a complicated system of circles. This model also became known as the Ptolemic System.
• 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.
• The North Star was believed to be in fixed position in the sky. However, when the Greeks traveled to places nearer the equator, like Egypt, they noticed that it is closer to the horizon.
• Aristotle


  A student of Plato and considered as one of the great philosophers of his time; his earth-centered view dominated for almost 2,000 years.
• Shadow


  A dark (real image) area where light from a light source is blocked by an opaque object.
• Retrograde Motion


  An apparent change in the movement of the planet through the sky.
• Winter Solstice


  A moment when the Sun's path in the sky is farthest south in the Northern Hemisphere or farthest north in the Southern Hemisphere.
• Summer Solstice


  The longest day of the year. In the Northern Hemisphere it is in June, while in the Southern Hemisphere it's in December.
• The Greeks are very much noted for their major contributions in different fields. They were not only great philosophers. They were great scientists and mathematicians as well.
• It was in Greece that the Golden Age of early astronomy was centered.
• The Greeks used the basics of geometry and trigonometry to measure the sizes and the distances of the sun and the moon.
• Geocentric view


  Earth was the center of the universe; hence, a motionless sphere. The sun, moon, Mercury, Venus, Mars, Jupiter, and Saturn orbited the Earth.
• Celestial sphere


  The transparent, hollow sphere located beyond the planets where the Greeks believed the stars traveled daily around the Earth.
• 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


  The North Star was believed to be at a fixed position in the sky.
• Aristotle argued that if the Moon and the Sun were both spherical, then perhaps, the Earth was also spherical.
• Eratosthenes gave the most accurate size during their time.
• Anaxagoras was able to explain what causes the phases of the moon. According to him, the moon shone only by reflected sunlight.
• 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
• 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.
• 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.
• Eratosthenes

  The first successful attempt to determine the size of the earth was made by him. 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

  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.
• This westward drift of the planets is called retrograde motion.
• planets orbited on small circles, called epicycles, revolving around large circles called deferents.