Download Observing the Solar System: A History

Observing the Solar System:
A History
Chapter 26.2
P577-580
Greek Observations:
Copernicus’s Idea
Wandering Stars:
Galileo’s Observations:
Brahe:
Newton:
Kepler:
Gravity:
Inertia:
Wandering Stars
• Greeks noticed 5 points of light that
appeared to wander amongst the stars.
• They called them Planets
– Greek for “wandering star”
Greek Observations
• Saw that these objects appeared to move and they
thought that the Earth remained stationary.
• They believed they were inside a rotating dome- called
the celestial sphere.
• Aristotle believed that the universe was perfect and finite
and that the Earth was stationary at the center.
• That theory is known as:
– Geocentric (Earth Centered) Model
Greek Observations
• Ptolemy:
• Puzzled by retrograde motion
• He created the Geocentric Model
– Planets orbit the Earth and move in smaller
circles.
Copernicus's Idea
• Early 1500’s Polish Astronomer
• Thought the Sun was at the center.
• Created the Heliocentric Model
– Helios- Greek for Sun
– The Earth and all the other planets move
around the sun.
– Included the six planets.
Galileo’s Observations
• Made two discoveries that supported the
heliocentric model.
– Saw 4 moons revolving around Jupiter
• Showed that not everything in the sky revolves
around the Earth.
– Venus goes through phases
• Venus could not go through phases if Earth was at
the center.
Heliocentric Model
Tycho Brahe
• A Danish Astronomer
• Made very accurate observations of the
positions of the planets for 20 years.
• He died before he could analyze his data.
Keppler
• 1600’s A German mathematician
• Analyzed Brahe’s data.
• Kepler discovered that the orbits of each
planet was an ellipse.
– An elongated circle or oval shape.
• His calculations fit Brahe’s observations.
Issac Newton
• An English scientist.
• Provided the answer to the question of
what keeps the planets in orbit.
– Concluded that gravity and inertia combine to
keep the planets in orbit.
Inertia
• An object’s tendency to move in a straight
line or to remain stationary.
• The more mass, the more inertia it has.
Gravity
• The force that pulls objects towards one
another.
• The strength depends on the masses and
the distances between them.