Topic 9 Lesson 1 Movements in Space

Night Sky

• Aryabhata- early astronomer, born in 476 CE in present day India

  • he said “the moon and the planets shine because they reflect light from the sun

  • his only tool for observation were his eyes

Stars, Planets, and the Moon

• earth’s moon is the largest and brightest object in our night sky

• satellite- a body that orbits a planet

  • earth’s only natural satellite is the moon

• star- a giant ball of superheated gas/plasma made of hydrogen and helium

• planet- an object that orbits the sun, large enough to have become rounded by its own gravity and has cleared its orbit of debris

  • we have 8 planets in our solar system

Meteors and Comets

• meteor- a streak of light made when a small piece of rock or ice burns up as it enters earth’s atmosphere

• meteoroid- small piece of rock or ice

• comet- a cold mixture of dust and ice that makes a long trail of light as it nears the sun

  • Halley’s Comet is the most famous comet

  • Halley predicted the appearance of the comet and it continues to appear about every 75 years

Constellations

• constellation- a pattern or group of stars that people imagine represents a figure, animal, or object

• in ancient Roman and Greek cultures, constellations went along with mythologies

  • we have 88 constellations

• they are named for people/animals from Greek Myths

Movement in the Sky

• the position of objects in the sky depend on the motions of earth

• stars usually appear to move from east to west

• caused by earth’s rotating

Seasonal Changes

• stars we see will vary from season to season

• changes are also caused by earth’s revolution/orbit

Planets

• they appear to move through a narrow band in the sky called the zodiac

• some planets are visible all night long

• mars, jupiter, and saturn can be seen after sunset

• venus and mercury can be seen only in the evening/morning

Models of the Solar System

• we have two solar system models

• ancient peoples noticed stars seemed relative to one another

1) Geocentric Model

• Aristotle thought earth was the center of our universe with planets and stars circling it

• geocentric- an earth centered model

• Ptolemy continued the model

  • his model had the planets making small circles as they moved along their orbits

  • epicyles are the small circles the planets make

  • this model explained the motions in the sky

  • his model was widely accepted for 1500 years after his death

2) Heliocentric Model

• Aristarchus- developed a sun centered model

• heliocentric- a sun centered model

  • this model was not well received

• 4 scientists worked to expand and prove the heliocentric model

  • Copernicus- said earth’s rotation/revolution around the sun explained movements

  • Brahe- much more accurate, began to observe that planet’s did not move in a circle around the sun

  • Kepler- Brahe’s assistant, proved that the shape of the planets orbit is an ellipse not a circle

  • Galileo- convinced others that the heliocentric model was correct

  • he used a telescope that he made to discover moons orbiting jupiter

  • the moons of jupiter are known as Galilean moons

  • this showed not everything in the sky travels around earth

Confirming the Heliocentric Model

• Galileo agreed with Copernicus that the sun was the center

• he discovered that venus goes through phases similar to the moon’s phases

• he reasoned that the geocentric model could not be true